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wasm-idle

wasm-idle

Executes C, C++, Objective-C, Fortran, COBOL, Python, Java, Rust, Go, D, C#, F#, VB.NET, Elixir, Erlang, Prolog, Gleam, Perl, Tcl, AWK, Pascal, Forth, J, BQN, Janet, Julia, Nim, Bash, ClojureScript, OCaml, JavaScript, TypeScript, AssemblyScript, WAT, WASM, Lua, Zig, Scheme, Ruby, Haskell, R, Octave, SQLite, DuckDB, and PHP code.

The browser-side C-family host is provided by @wasm-idle/llvm-core. Compiler source pins, patches, and reproducible asset builds live in seo-rii/wasm-llvm; wasm-idle loads the generated artifacts from external URLs instead of embedding them in npm packages.

Language support policy

wasm-idle language support must run user code through the real language implementation in the browser, normally via a WebAssembly compiler, interpreter, or runtime. Do not add handwritten parsers, translators, emulators, or "subset" executors as language support. A language should be listed only after normal user code runs on that actual runtime and stdin/stdout behavior, or a documented stdin limitation, is covered by tests.

Support matrix

All execution entries run in the browser through real runtime, compiler, or interpreter implementations. Editor support lists browser LSP/compiler diagnostics when wired; syntax means Monaco syntax highlighting only. C, C++, and wasm32-wasip1 Rust use the browser LLDB/WAMR debug runtime; the remaining debug-enabled languages retain wasm-idle's trace controls.

Language Browser runtime/compiler Stdin Editor support Debug
C @wasm-idle/llvm-core / Clang WASI Yes clangd LLDB
C++ @wasm-idle/llvm-core / Clang WASI Yes clangd LLDB
Objective-C GNUstep libobjc2 + @wasm-idle/llvm-core Yes clangd Trace
Python Pyodide Yes Python LSP Trace
Java TeaVM Yes syntax -
Rust wasm-rust / browser rustc Yes rustc diagnostics LLDB
Go wasm-go / browser Go compiler Yes compiler diagnostics Trace
D wasm-d Yes syntax -
C# wasm-dotnet Yes compiler diagnostics -
F# wasm-dotnet Yes compiler diagnostics -
VB.NET wasm-dotnet Yes compiler diagnostics -
Elixir AtomVM / Popcorn Yes syntax -
Erlang AtomVM / Popcorn Yes syntax -
Prolog SWI-Prolog WASM worker Yes syntax -
Gleam Gleam precompiled browser runtime Yes compiler diagnostics -
Perl Perl WASM worker Yes syntax -
Tcl Wacl Tcl WASM worker Yes syntax -
AWK GoAWK WASM worker Yes syntax -
Pascal pas2js worker Yes syntax -
Forth WAForth WASM worker Yes syntax -
J J playground WASM worker Yes syntax -
BQN CBQN WASM worker Yes syntax -
Janet Janet VM WASM worker Yes syntax -
Julia Julia 1.3.0-DEV.560 legacy WASM worker Yes syntax -
Nim Nim 2.2.4 WASM + clang/lld WASM Yes syntax -
Bash GNU Bash WASIX / Wasmer SDK Yes syntax -
ClojureScript cljs.js self-hosted compiler Yes syntax -
TinyGo wasm-tinygo Yes syntax -
OCaml wasm-of-js-of-ocaml / js_of_ocaml Yes syntax -
JavaScript wasm-typescript / TypeScript service Yes TypeScript LSP -
TypeScript wasm-typescript / TypeScript service Yes TypeScript LSP -
AssemblyScript AssemblyScript compiler Yes AssemblyScript LSP -
WAT WABT Yes WAT LSP -
WASM Browser WebAssembly + WASI shim Yes syntax -
Lua Wasmoon Yes syntax -
Zig zig_small.wasm Yes syntax -
Scheme Puppy Scheme / wasm-lisp Yes syntax -
Ruby CRuby WASI Yes syntax -
Haskell ghc-in-browser Yes syntax -
Fortran f2c + @wasm-idle/llvm-core Yes Fortran LSP -
COBOL GnuCOBOL 3.2 + @wasm-idle/llvm-core Yes syntax -
R WebR Yes syntax -
Octave wasm-octave Yes syntax -
DuckDB DuckDB-Wasm Files DuckDB LSP -
SQLite sql.js n/a syntax -
PHP PHP 8.4 / php-wasm Yes syntax -

Browser LLDB debug runtime

Normal execution still compiles and instantiates the user module with the browser WebAssembly engine and the existing WASI host. C, C++, and wasm32-wasip1 Rust debug sessions use a separate, lazy-loaded path:

Monaco / debug UI
  ↕ DAP over a SharedArrayBuffer byte stream
LLDB worker (ProcessWasm + DWARF)
  ↕ GDB RSP over a separate SharedArrayBuffer byte stream
WAMR target worker (classic interpreter + source-debug stub)
  ↕
program.wasm + embedded DWARF + WASI

The compiler writes stable /workspace/... paths and embedded DWARF at -O0. The target is loaded before LLDB attaches; breakpoints and configurationDone are completed before WAMR starts the guest. Program output, input, lifecycle control, DAP, and RSP use separate logical streams. Breakpoints are retained per source path, so switching between C/C++ workspace files does not leak line numbers into another file and changes made while compilation is in flight are applied when the debug target connects. @wasm-idle/debug remains a code-only UI/adapter package, while @wasm-idle/llvm-core/debug owns the browser session and wasm-llvm owns the pinned LLDB/WAMR producers and binary manifests.

Debugging requires SharedArrayBuffer and a cross-origin-isolated deployment. The LLDB and WAMR assets are not downloaded until a supported debug session starts. If the LLDB manifest is absent, invalid, or does not advertise the required breakpoint/step/stack/local capabilities, the playground labels that run as a trace fallback and keeps the existing instrumentation debugger available. Build and verify both producers using producer/lldb-browser and producer/wamr-browser, then assemble them with the Clang release:

Stable v1 is release-qualified on 64-bit desktop Chromium on Linux. It supports one active debug session for wasm32-wasi Preview 1 C/C++ and wasm32-wasip1 Rust artifacts produced by the pinned toolchains at -O0 with embedded DWARF. Debug starts a new, single-threaded WAMR classic interpreter instance; it does not attach to a browser-engine run or preserve that run's live state, and runtime-specific behavior can differ. Trace fallback is selected only before an LLDB session is established; an LLDB or WAMR failure ends that session instead of silently changing debugger semantics.

Full expression evaluation, conditional/log/data breakpoints, variable mutation, restart, standalone terminate, optimized-debug guarantees, C++ exception support, STL pretty-printers, wasm64, guest threads, reverse debugging, SIMD, multi-module guests, and Rust WASI Preview 2/3 debugging are outside the v1 support boundary.

cd ../wasm-llvm
WASM_LLVM_LLDB_ARTIFACT_DIR=/path/to/lldb-artifacts \
WASM_LLVM_WAMR_ARTIFACT_DIR=/path/to/wamr-artifacts \
pnpm prepare:clang-release

cd ../wasm-idle
WASM_RUST_PRODUCER_OUTPUT_ROOT=/path/to/rust-producer-output \
pnpm --dir runtimes/wasm-rust build:producer
pnpm sync:wasm-rust
pnpm sync:wasm-debug ../wasm-llvm/out/clang-browser
WASM_IDLE_BROWSER_SERVER_MODE=dev pnpm test:browser:debug:lldb

The synchronized manifest rejects missing hashes, incompatible Clang/LLDB revisions, and stale worker sidecars. The strict browser test covers real C, C++, and Rust breakpoint, step, output, and termination paths and rejects trace fallback or a missing debug asset. The Rust producer build is required for LLDB metadata; the historical split-runtime build intentionally lacks exact compiler provenance and is rejected instead of starting a potentially incompatible debugger.

Runtime details

Package/version base names the deployed static module or manifest and its producer package, or the browser-side package/workspace runtime that backs each row. Static ESM entries are page assets loaded over HTTP on demand, not files embedded in the published npm packages. Execution defaults / flags lists the default targets and flags wasm-idle applies, plus the public per-run options that change execution. Customization lists the runtimeAssets fields and matching PUBLIC_WASM_* env overrides when they exist.

Language / IDs Package/version base Execution defaults / flags Customization
C
C		 @wasm-idle/llvm-core@1.0.0 / Clang 22.1.8 WASI sysroot from the wasm-llvm producer clang for wasm32-wasi; default -std=gnu11; LLDB mode compiles untouched source with embedded DWARF at -g -O0 and runs it in WAMR; normal runs still use the browser WASI host; supports stdin and programArgs runtimeAssets.clang.baseUrl/loader or rootUrl; compileArgs, programArgs, cVersion, activePath, workspaceFiles, debugMode, breakpoints, pauseOnEntry
C++
CPP		 @wasm-idle/llvm-core@1.0.0 / Clang 22.1.8 WASI sysroot from the wasm-llvm producer clang++ for wasm32-wasi; default -std=gnu++2a; LLDB mode compiles untouched source with embedded DWARF at -g -O0 and runs it in WAMR; normal runs still use the browser WASI host; supports stdin and programArgs runtimeAssets.clang.baseUrl/loader or rootUrl; compileArgs, programArgs, cppVersion, activePath, workspaceFiles, debugMode, breakpoints, pauseOnEntry
Objective-C
OBJC		 GNUstep libobjc2 v2.3 assets from the wasm-llvm producer + @wasm-idle/llvm-core@1.0.0 clang -x objective-c -fobjc-runtime=gnustep-2.0 -fblocks for wasm32-wasi; links libobjc.a, libgnustep-base.a, and libffi.a when Foundation is imported; Foundation headers are inlined from foundation-headers.json; includes a constructor wrapper for Objective-C class registration; auto-compiles .m/.mm/.c workspace files; trace debug instruments active source and uses wasm-idle controls; supports stdin and programArgs; large Objective-C assets may be served as gzip-only .gz files through the service worker or worker fallback runtimeAssets.objectivec.baseUrl/libobjcUrl/headersUrl/libgnustepBaseUrl/libgnustepBaseObjectUrl/foundationHeadersUrl/libffiUrl or PUBLIC_WASM_OBJECTIVEC_*; runtimeAssets.clang.baseUrl/loader for the clang toolchain; activePath, workspaceFiles, compileArgs, debug, breakpoints, pauseOnEntry
Python
PYTHON3		 static ESM static/pyodide/pyodide.mjs / pyodide@0.29.3 loads pyodide.mjs, pyodide.asm.js, pyodide.asm.wasm, and python_stdlib.zip from the configured static asset tree on demand; supports stdin, workspace files, and trace debugging runtimeAssets.python.baseUrl/loader or rootUrl; stdin, activePath, workspaceFiles, debug, breakpoints, pauseOnEntry, debugPath
Java
JAVA		 @wasm-idle/runtime-teavm@0.0.0 / TeaVM compiler assets compiler.wasm compiles Java to browser WASM/JS; supports stdin and programArgs runtimeAssets.java.baseUrl/loader or rootUrl
Rust
RUST		 wasm-rust@0.1.0 / rust-1.99.0-browser-integrated-v1 + integrated LLVM/LLD 22.1.8 from the wasm-llvm producer; exact rustc/LLVM provenance is recorded for LLDB compatibility browser host wasm32-wasip1-threads; default target wasm32-wasip1, selectable wasm32-wasip1, wasm32-wasip2, wasm32-wasip3; LLDB mode is currently limited to wasm32-wasip1 and emits embedded DWARF with -C debuginfo=2 -C opt-level=0; normal Preview 1/2/3 execution remains unchanged; supports stdin and programArgs runtimeAssets.rust.compilerUrl, runtimeAssets.rust.debugModuleUrl, or PUBLIC_WASM_RUST_COMPILER_URL; rootUrl, rustTargetTriple, programArgs, debugMode; compiler requests accept edition, crateType, extendedTimeout, log, and onProgress; runtime manifest controls compiler memory, timeout, and shared workspace size
Go
GO		 wasm-go@0.1.0 / go1.26.1 default target wasip1/wasm; selectable wasip1/wasm, wasip2/wasm, wasip3/wasm, js/wasm; supports stdin and programArgs runtimeAssets.go.compilerUrl or PUBLIC_WASM_GO_COMPILER_URL; goTarget, programArgs
D
D		 wasm-d@0.1.0 / ldc-1.42.0-wasi-smoke ldc2 -conf=/toolchain/etc/ldc2.conf -mtriple=wasm32-wasi -c then wasm-ld to WASI preview1; supports stdin and programArgs runtimeAssets.d.moduleUrl or PUBLIC_WASM_D_MODULE_URL; activePath, programArgs
C#
CSHARP		 wasm-dotnet@0.1.0 / .NET 9.0.16 browser-wasm / Roslyn C# 4.14.0 CSharpCompilationOptions(OutputKind.ConsoleApplication); concurrentBuild=false; target browser-wasm; language-specific AOT bundle runtime/csharp/; supports stdin and programArgs runtimeAssets.dotnet.moduleUrl or PUBLIC_WASM_DOTNET_MODULE_URL; programArgs, LSP on/off
F#
FSHARP		 wasm-dotnet@0.1.0 / .NET 9.0.16 browser-wasm / FCS 43.12.204 / FSharp.Core 10.1.204 fsc.exe --target:exe --targetprofile:netcore --noframework --simpleresolution --nowin32manifest --debug- --optimize-; language-specific AOT bundle runtime/fsharp/; supports stdin and programArgs runtimeAssets.dotnet.moduleUrl or PUBLIC_WASM_DOTNET_MODULE_URL; programArgs, LSP on/off
VB.NET
VBNET		 wasm-dotnet@0.1.0 / .NET 9.0.16 browser-wasm / Roslyn Visual Basic 4.14.0 VisualBasicCompilationOptions(OutputKind.ConsoleApplication); concurrentBuild=false, OptionStrict=Off, OptionInfer=On, OptionExplicit=On; target browser-wasm; language-specific AOT bundle runtime/vbnet/; supports stdin and programArgs runtimeAssets.dotnet.moduleUrl or PUBLIC_WASM_DOTNET_MODULE_URL; programArgs, LSP on/off
Elixir
ELIXIR		 wasm-elixir asset bundle / @swmansion/popcorn@0.2.2 Popcorn/AtomVM bundle bundle.avm; supports stdin runtimeAssets.elixir.bundleUrl or PUBLIC_WASM_ELIXIR_BUNDLE_URL
Erlang
ERLANG		 wasm-elixir asset bundle / @swmansion/popcorn@0.2.2 Popcorn/AtomVM bundle bundle.avm; supports stdin runtimeAssets.erlang.bundleUrl or PUBLIC_WASM_ERLANG_BUNDLE_URL; falls back to Elixir bundle URL
Prolog
PROLOG		 swipl-wasm@8.0.1 synced into static/wasm-prolog static worker runs SWI-Prolog; supports stdin and programArgs runtimeAssets.prolog.baseUrl/runtimeAssets.prolog.workerUrl or PUBLIC_WASM_PROLOG_BASE_URL/PUBLIC_WASM_PROLOG_WORKER_URL; programArgs, activePath, workspaceFiles
Gleam
GLEAM		 @live-codes/gleam-precompiled@0.5.0 static worker Gleam worker compiles/runs browser output with source manifest; supports stdin runtimeAssets.gleam.baseUrl/workerUrl/manifestUrl or PUBLIC_WASM_GLEAM_*; programArgs, workspaceFiles
Perl
PERL		 WebPerl v0.09-beta (webperl_prebuilt_v0.09-beta.zip) host-verifies the manifest, stored assets, logical hashes, and profile-bound one-shot runner before executing emperl; supports stdin and programArgs explicit runtimeAssets.perl.baseUrl/workerUrl/manifestUrl overrides require one complete profile-and-runner receipt bundle; URL-only PUBLIC_WASM_PERL_* overrides fail closed; programArgs, activePath, workspaceFiles
Tcl
TCL		 Wacl Tcl 2017-05-29 (wacl.zip) host-verifies the manifest, stored assets, logical hashes, and profile-bound one-shot runner before executing Wacl Tcl; supports stdin and programArgs bundled mirrors may set runtimeAssets.tcl.baseUrl/workerUrl/manifestUrl or PUBLIC_WASM_TCL_BASE_URL/PUBLIC_WASM_TCL_WORKER_URL; custom executable bytes require one complete profile-and-runner receipt bundle; programArgs, activePath, workspaceFiles
AWK
AWK		 GoAWK v1.31.0 / go1.25.3 static worker runs goawk.wasm; supports stdin and programArgs runtimeAssets.awk.baseUrl/runtimeAssets.awk.workerUrl or PUBLIC_WASM_AWK_BASE_URL/PUBLIC_WASM_AWK_WORKER_URL; programArgs, activePath, workspaceFiles
Pascal
PASCAL		 pas2js 3.2.1 (9ac46614dc82) static worker compiles with pas2js then runs JS; supports stdin runtimeAssets.pascal.baseUrl/runtimeAssets.pascal.workerUrl or PUBLIC_WASM_PASCAL_BASE_URL/PUBLIC_WASM_PASCAL_WORKER_URL; programArgs, activePath, workspaceFiles
Forth
FORTH		 waforth@0.20.1 / static worker WAForth worker; supports stdin and programArgs runtimeAssets.forth.baseUrl/runtimeAssets.forth.workerUrl or PUBLIC_WASM_FORTH_BASE_URL/PUBLIC_WASM_FORTH_WORKER_URL; programArgs, activePath, workspaceFiles
J
J		 jsoftware-j-playground static worker J playground worker; supports stdin and programArgs runtimeAssets.j.baseUrl/runtimeAssets.j.workerUrl or PUBLIC_WASM_J_BASE_URL/PUBLIC_WASM_J_WORKER_URL; programArgs, activePath, workspaceFiles
BQN
BQN		 CBQN static worker / Emscripten 3.1.8 CBQN worker; supports stdin and programArgs runtimeAssets.bqn.baseUrl/runtimeAssets.bqn.workerUrl or PUBLIC_WASM_BQN_BASE_URL/PUBLIC_WASM_BQN_WORKER_URL; programArgs, activePath, workspaceFiles
Janet
JANET		 Janet 1.41.3-dev / Emscripten 3.1.8 opaque vendored bundle host-verifies the manifest, stored assets, logical hashes, and profile-bound one-shot runner before executing the Janet VM; supports stdin and programArgs explicit runtimeAssets.janet.baseUrl/workerUrl/manifestUrl overrides require one complete profile-and-runner receipt bundle; URL-only PUBLIC_WASM_JANET_* overrides fail closed; programArgs, activePath, workspaceFiles
Julia
JULIA		 @chriskoch/julia-wasm@1.0.4 host-verifies the manifest, stored assets, logical hashes, and profile-bound one-shot runner before executing the legacy Julia VM; supports stdin and activePath explicit runtimeAssets.julia.baseUrl/workerUrl/manifestUrl overrides require one complete profile-and-runner receipt bundle; URL-only PUBLIC_WASM_JULIA_* overrides fail closed; activePath
Nim
NIM		 Nim 2.2.4 / benagastov Nim-WASM-Compiler with clang/lld WASM host-verifies the manifest, eight stored assets, logical hashes, and profile-bound one-shot runner before compiling Nim to C and linking with clang/lld WASM in a disposable worker; supports stdin, programArgs, and activePath explicit runtimeAssets.nim.baseUrl/workerUrl/manifestUrl overrides require one complete profile-and-runner receipt bundle; URL-only PUBLIC_WASM_NIM_* overrides fail closed; programArgs, activePath
Bash
BASH		 @wasm-idle/runtime-bash@0.1.0 / GNU Bash WASIX + receipt-pinned @wasmer/sdk@0.9.0 profile host-verifies one profile manifest, the stored SDK JavaScript, Wasmer Wasm, and WEBc before starting a fixed worker generation with no runtime-asset fetches; invokes bash -c <code> <activePath> ...programArgs and supports stdin, programArgs, activePath, and workspaceFiles rootUrl mirrors reuse the bundled profile; explicit runtimeAssets.bash.baseUrl/manifestUrl/moduleUrl/wasmerWasmUrl/webcUrl overrides require one complete profile; workerUrl is rejected; stdin, programArgs, activePath, workspaceFiles
ClojureScript
CLOJURESCRIPT		 @wasm-idle/runtime-clojurescript@0.1.0 / ClojureScript 1.12.134 static worker compiles and evaluates with the official cljs.js self-hosted compiler; supports stdin, programArgs, activePath, and workspaceFiles runtimeAssets.clojurescript.baseUrl/runtimeAssets.clojurescript.workerUrl or PUBLIC_WASM_CLOJURESCRIPT_BASE_URL/PUBLIC_WASM_CLOJURESCRIPT_WORKER_URL; programArgs, activePath, workspaceFiles
TinyGo
TINYGO		 wasm-tinygo@0.0.0 / upstream TinyGo 0.40.1 browser toolchain receipt-verifies and runs upstream cmd/go plus TinyGo in a disposable capped Worker; targets wasip1; supports stdin, programArgs, workspaceFiles, hosted C++ without exceptions/RTTI, and offline vendor/modules.txt runtimeAssets.tinygo.moduleUrl/assetLoader; PUBLIC_WASM_TINYGO_MODULE_URL, execution/workspace resource limits, programArgs
OCaml
OCAML		 wasm-of-js-of-ocaml@0.1.0 / js_of_ocaml + wasm_of_ocaml default backend wasm; selectable wasm, js; ocamlWasmBinaryenMode fast, full; supports stdin runtimeAssets.ocaml.moduleUrl/manifestUrl or PUBLIC_WASM_OCAML_*; ocamlBackend
JavaScript
JAVASCRIPT		 wasm-typescript@0.1.0 / @swc/wasm-typescript@1.15.33 TypeScript service transpiles JS/TS and runs in browser sandbox; supports stdin and programArgs runtimeAssets.typescript.moduleUrl/libUrl or PUBLIC_WASM_TYPESCRIPT_MODULE_URL
TypeScript
TYPESCRIPT		 wasm-typescript@0.1.0 / @swc/wasm-typescript@1.15.33 TypeScript service transpiles then runs in browser sandbox; supports stdin and programArgs runtimeAssets.typescript.moduleUrl/libUrl or PUBLIC_WASM_TYPESCRIPT_MODULE_URL
AssemblyScript
ASSEMBLYSCRIPT		 static ESM static/wasm-assemblyscript/runtime.mjs produced from assemblyscript@0.28.17 + @assemblyscript/loader@0.28.17 asc <activePath> --outFile module.wasm --runtime incremental --bindings raw --optimize --exportRuntime; runs the emitted WASM through WASI/browser imports and supports stdin runtimeAssets.assemblyscript.moduleUrl or PUBLIC_WASM_ASSEMBLYSCRIPT_MODULE_URL or rootUrl; stdin, activePath, workspaceFiles
WAT
WAT		 wasm-wat@0.1.0 / wabt@1.0.39 WABT parses WAT to WASM then runs through WASI shim; supports stdin and programArgs runtimeAssets.wat.moduleUrl or PUBLIC_WASM_WAT_MODULE_URL; programArgs
WASM
WASM		 Browser WebAssembly + @bjorn3/browser_wasi_shim@0.4.2 loads provided WASM bytes and executes with WASI preview1 imports; supports stdin and programArgs programArgs, stdin, activePath
Lua
LUA		 wasm-lua@0.1.0 / wasmoon@1.16.0 Wasmoon Lua VM; supports stdin and programArgs runtimeAssets.lua.moduleUrl or PUBLIC_WASM_LUA_MODULE_URL; programArgs
Zig
ZIG		 static wasm-zig assets / zig_small.wasm + std.tar.gz native gzip delivery for the tar standard library; default target wasm64-wasi; Zig compile args are appended; supports stdin, compileArgs, programArgs runtimeAssets.zig.compilerUrl/stdlibUrl or PUBLIC_WASM_ZIG_*; zigTargetTriple, activePath, workspaceFiles
Scheme
LISP		 wasm-lisp@0.1.0 / Puppy Scheme WASM component receipt-verified Puppy Scheme compiler/runtime; supports stdin and programArgs runtimeAssets.lisp.{moduleUrl,manifestUrl,manifestFingerprint} or PUBLIC_WASM_LISP_{MODULE_URL,MANIFEST_URL,MANIFEST_FINGERPRINT}; programArgs
Ruby
RUBY		 static ESM static/wasm-ruby/runtime.mjs produced from @ruby/3.4-wasm-wasi@2.9.3-2.9.4 + @ruby/wasm-wasi@2.9.3-2.9.4 CRuby 3.4 WASI runtime loads ruby+stdlib.wasm on demand; supports stdin, programArgs, and workspace files runtimeAssets.ruby.moduleUrl/wasmUrl or PUBLIC_WASM_RUBY_MODULE_URL/PUBLIC_WASM_RUBY_WASM_URL or rootUrl; stdin, programArgs, workspaceFiles
Haskell
HASKELL		 ghc-in-browser / GHC 9.14.0.20251031 WASI rootfs loads dyld.mjs, rootfs.tar.zst, bsdtar.wasm; compileArgs become GHC args, otherwise legacy args become GHC args runtimeAssets.haskell.moduleUrl/rootfsUrl/bsdtarUrl; mainSoPath, searchDirs, activePath, workspaceFiles
Fortran
FORTRAN		 Netlib f2c 2022-09-09 + @cowasm/f2c 1.0.0 libf2c + @wasm-idle/llvm-core@1.0.0 runs f2c.wasm in WASI, compiles generated C with the llvm-core Clang host, links libf2c.a, then executes the resulting WASI module with stdin and programArgs runtimeAssets.fortran.baseUrl/f2cWasmUrl/libf2cUrl/f2cHeaderUrl/analyzerUrl or PUBLIC_WASM_FORTRAN_*; runtimeAssets.clang.baseUrl/loader for the C backend; activePath, workspaceFiles, compileArgs
COBOL
COBOL		 GnuCOBOL 3.2 + GMP 6.3.0 assets from the wasm-llvm producer + @wasm-idle/llvm-core@1.0.0 native gzip delivery for the frontend Wasm and filesystem tar assets; translates free-format COBOL with the real GnuCOBOL cobc frontend, compiles the generated C with the llvm-core Clang host, links libcob/GMP, and executes the resulting WASI module with stdin and programArgs runtimeAssets.cobol.baseUrl or PUBLIC_WASM_COBOL_BASE_URL; runtimeAssets.clang.baseUrl/loader for the C backend; activePath, workspaceFiles, compileArgs
R
R		 versioned static static/webr/<hash>/webr.js / webr@0.6.0 loads the browser ESM entry webr.js and its WebR runtime files from the configured static asset tree on demand; supports stdin, programArgs, and workspace files runtimeAssets.r.baseUrl or PUBLIC_WASM_R_BASE_URL; stdin, programArgs, activePath, workspaceFiles
Octave
OCTAVE		 Octave 10.3.0 (octave-10.3.0-pl5321h996e327_3.tar.bz2) Octave CLI Emscripten worker; supports stdin and programArgs runtimeAssets.octave.baseUrl/workerUrl/manifestUrl or PUBLIC_WASM_OCTAVE_*
DuckDB
DUCKDB		 static ESM static/wasm-duckdb/runtime.mjs produced from @duckdb/duckdb-wasm@1.33.1-dev45.0 selects the best DuckDB-Wasm MVP/EH bundle on demand and creates a fresh in-memory database per run; stdin is registered as stdin.txt and /dev/stdin rather than terminal stdin runtimeAssets.duckdb.moduleUrl or PUBLIC_WASM_DUCKDB_MODULE_URL or rootUrl; stdin, activePath, workspaceFiles
SQLite
SQLITE		 static ESM static/wasm-sqlite/runtime.mjs produced from sql.js@1.14.1 sql.js loads sql-wasm.wasm on demand and executes SQL in a fresh in-memory database; terminal stdin is not applicable runtimeAssets.sqlite.moduleUrl/wasmUrl or PUBLIC_WASM_SQLITE_MODULE_URL/PUBLIC_WASM_SQLITE_WASM_URL or rootUrl; workspaceFiles
PHP
PHP		 static ESM static/wasm-php/runtime.mjs prebuilt by the standalone producers/wasm-php producer from @php-wasm/web-8-4@3.1.34 + @php-wasm/universal@3.1.34 fixed PHP 8.4 php-wasm runtime; injects $argv/$argc and runs the active workspace script with php.run; supports stdin and programArgs; there is no runtime version selector runtimeAssets.php.moduleUrl or PUBLIC_WASM_PHP_MODULE_URL or rootUrl; stdin, programArgs, activePath, workspaceFiles

Blocked candidates

These languages are intentionally not part of the execution support matrix yet. They should stay out of supportedLanguages until the blocker is resolved with a real browser runtime/compiler and stdin/stdout coverage.

Candidate Candidate IDs Current evidence Blocker Required follow-up
Modern Fortran F90, F95 FORTRAN now runs through f2c/libf2c, while static/wasm-fortran still packages LFortran analyzer assets LFortran WASM/WAT stdin codegen still aborts and the C backend reports visit_FileRead() not implemented; f2c covers Fortran 77-style code but is not a full modern Fortran compiler Package a real browser modern Fortran compiler/runtime with stdin-capable codegen before advertising F90/F95 as first-class runtimes
Crystal CRYSTAL No browser Crystal compiler/runtime assets are packaged in this repository Crystal cannot be treated as syntax-only or as a wasm-idle-authored translator/subset Find or build a browser-hosted real Crystal compiler/runtime path with stdin/stdout coverage before registering the language
Swift SWIFT Swift.org documents Wasm support through a native Swift 6.x toolchain plus a Wasm SDK, and SwiftWasm Pad uses a backend compile service; no browser-hosted swiftc/SwiftPM runtime asset is packaged here Swift cannot be implemented as a wasm-idle-authored parser/runtime subset or as a remote compile service; the playground needs a redistributable browser-hosted real Swift compiler path Build or source a browser-hosted Swift compiler/SwiftPM runtime bundle, prove stdin/stdout execution for generated WASI modules, then register SWIFT as a first-class runtime

Monorepo layout

wasm-idle is managed as a pnpm workspace. Language-independent app code remains here while large toolchains can be consumed from pinned external runtime repositories:

  • packages/core: framework-neutral contracts, runtime asset keys, progress helpers, and playground binding helpers.
  • packages/debug: optional debug session controller, language adapters, expression helpers, and Monaco integration built on the contracts from @wasm-idle/core.
  • packages/llvm-core: code-only browser hosts for shared memory, MemFS, tar, WASI, Clang, COBOL, and Objective-C execution. Every compiler, sysroot, archive, and worker asset is supplied through an explicit HTTP(S) URL.
  • packages/lsp: code-only browser language-server hosts. TypeScript libraries, SQL engines, clangd, and other language-tool assets are supplied through explicit runtime URLs.
  • seo-rii/wasm-llvm: external producer repository for compiler source pins, patches, reproducible builds, manifests, and asset verification. Its producer/rust-browser source build owns the current Rust 1.99 compiler, matching LLVM 22 code generator, and in-process LLD; it is not consumed as an npm runtime package.
  • packages/svelte: Svelte store/binding helpers around @wasm-idle/core.
  • packages/terminal: optional Svelte/xterm terminal UI that consumes an injected playground binding without adding browser UI dependencies to the root runtime package.
  • packages/react: React hooks around @wasm-idle/core.
  • packages/vue: Vue composables around @wasm-idle/core.
  • packages/node: Node.js host helpers for Node-capable sandbox loaders.
  • runtimes/*: imported runtime/compiler packages such as wasm-rust, wasm-of-js-of-ocaml, wasm-go, wasm-dotnet, wasm-typescript, wasm-wat, wasm-lua, wasm-lisp, wasm-elixir, wasm-tcl, wasm-awk, wasm-forth, wasm-j, wasm-bqn, wasm-janet, pyodide, teavm, assemblyscript, ruby, r, and js-sandbox.
  • runtimes/wasm-tinygo: the public TINYGO browser compiler consumer plus an explicitly labeled legacy AST-to-C development harness. Static releases publish only the receipt-verified upstream consumer and its source-pinned toolchain assets.
  • producers/wasm-php: standalone, locked producer for the checked-in PHP 8.4 page asset. It is outside the root workspace and is never published as an npm package.
  • static/wasm-zig, static/wasm-haskell, static/wasm-julia, and static/wasm-nim: bundled browser runtime and compiler assets synced from upstream asset builds rather than local workspace packages.
  • tools/*: migrated local toolchain projects that are too broad or infrastructure-heavy to run as normal runtime workspace packages. tools/dool contains the Docker judge backend for Elixir and the other server-side language runners.

Useful workspace commands:

pnpm workspace:list
pnpm build:packages
pnpm check:packages
pnpm build:runtimes
pnpm check:runtimes
pnpm sync:runtime list
pnpm sync:runtimes

The runtime sync scripts default to runtimes/<name>/dist; optional source and target arguments are for alternate build directories inside the current checkout. PHP is the exception: sync:wasm-php consumes producers/wasm-php/dist or WASM_IDLE_WASM_PHP_DIST.

Published packages are built in workspace dependency order. Before publishing, run:

pnpm verify:package

The smoke check packs the root library and its public workspace dependencies, installs the tarballs into a temporary project, and imports each public entry point.

Package-backed browser runtimes are converted into page-owned static ESM assets with:

pnpm run build:static-runtime-modules

This producer step writes runtime.mjs trees under static/wasm-assemblyscript/, static/wasm-duckdb/, static/wasm-ruby/, and static/wasm-sqlite/. It also writes the Wasmer SDK compatibility files and the unified Bash runtime profile under static/wasm-bash/ through the same rollback-capable Bash producer used by sync:wasm-bash. The browser consumes only the profile's opaque, receipt-pinned storage paths; these files are deployed page assets, not npm package contents.

PHP is built independently under producers/wasm-php, with its own lockfile and exact @php-wasm/web-8-4@3.1.34 and @php-wasm/universal@3.1.34 dependencies. Refresh the checked-in page asset only when changing that producer:

pnpm --dir producers/wasm-php install --frozen-lockfile
pnpm --dir producers/wasm-php build
pnpm --dir producers/wasm-php verify
pnpm run sync:wasm-php
pnpm run build:static-runtime-modules
pnpm run compress:static-runtimes

build:static-runtime-modules regenerates the shared module cache key after the PHP manifest changes, but validates rather than rebuilds PHP. page:build neither installs nor bundles PHP packages; it validates the manifest, logical byte sizes, and SHA-256 hashes of the checked-in static/wasm-php/ output before consuming it. The runtime exposes PHP 8.4 only; there is no runtime PHP version selector.

Java uses TeaVM's browser compiler/runtime. TeaVM compiler/runtime/classlib assets are bundled under static/teavm/ by default, and the asset base URL can be overridden with PUBLIC_TEAVM_BASE_URL.

Pyodide's pyodide.mjs and core assets are served from static/pyodide/ and loaded on demand by both Python execution and Python LSP workers. Refresh them after bumping the pyodide package with:

cd wasm-idle
pnpm run sync:pyodide

WebR's browser ESM entry webr.js and runtime files are served from a fingerprinted directory under static/webr/. R execution and R LSP workers share that static asset tree. Refresh it after bumping webr with:

cd wasm-idle
pnpm run sync:webr

Elixir and Erlang browser execution use an AtomVM/Popcorn AVM bundle. The Popcorn eval-in-wasm source and vendored Popcorn Elixir build dependency now live under runtimes/wasm-elixir/; rebuild and sync with:

cd wasm-idle
pnpm --dir runtimes/wasm-elixir run bundle
pnpm run sync:wasm-elixir

Erlang support uses Popcorn's upstream eval_erlang and eval_erlang_module paths. This is not a handwritten wasm-idle subset, but it inherits AtomVM/Popcorn runtime limits and is not full Erlang/OTP ERTS coverage. Some OTP paths that rely on missing NIFs can fail in the current bundle, so the browser starter and stdin coverage use io:get_line/io:format only.

Julia browser execution uses the @chriskoch/julia-wasm@1.0.4 asset bundle under static/wasm-julia/. Despite the package and bundled README version, the verified runtime reports VERSION == v"1.3.0-DEV.560"; wasm-idle therefore labels it as a legacy development runtime. Refresh the vendored worker/runtime assets with:

cd wasm-idle
pnpm run sync:wasm-julia

Nim browser execution uses the benagastov/Nim-WASM-Compiler asset pipeline under static/wasm-nim/: Nim 2.2.4 compiled to WebAssembly emits C, then bundled clang/lld WebAssembly assets link a runnable WASI module. Refresh the vendored worker/runtime assets with:

cd wasm-idle
pnpm run sync:wasm-nim

Rust browser integration

The demo app bundles the workspace wasm-rust browser compiler under static/wasm-rust/ and points the example Terminal at /wasm-rust/index.js by default. Refresh it with:

pnpm --dir runtimes/wasm-rust build
pnpm run sync:wasm-rust

The built-in Rust route supports wasm32-wasip1, wasm32-wasip2, and wasm32-wasip3. The page exposes a target selector when Rust is active, defaults to wasm32-wasip1, and persists that choice in local storage. The compiler module, rustc, sysroot, and component tooling remain unloaded until Rust is selected; LSP assets remain unloaded until the LSP toggle is enabled.

TinyGo browser integration

TINYGO is a public wasip1 playground language backed by the independent upstream.js consumer. It never falls back to wasm-idle's older Go AST-to-C porting harness: the static sync allowlist excludes runtime.js, its runtime chunks, emception, and the legacy compiler payload. The legacy code remains in runtimes/wasm-tinygo only for local compiler-port development and is explicitly classified as wasm-idle-go-ast-to-c-subset.

The sibling wasm-llvm/producer/tinygo-browser producer pins upstream TinyGo 0.40.1, go-llvm, TinyGo LLVM 20.1.1, Go 1.24.6, and WASI SDK 33. The public consumer hash-verifies both producer receipts, the upstream compiler, reduced TinyGo/Go root, cmd/go WASI package-graph provider, and raw LLD before compiling. It derives package JSON from the supplied module workspace, validates every compiler/link-plan handoff, links with raw LLD, and finalizes with pinned Binaryen 129.

Compile protocol v6 covers generated go:embed objects, CGo C, hosted libc++/libc++abi C++17 without exceptions/RTTI/global constructors, preprocessed Clang assembly, exact allowed CXXFLAGS, and restricted #cgo LDFLAGS. Offline external modules require a complete vendor/modules.txt tree; there is no network module fallback. Package-graph and compile work run inside disposable Workers with fail-closed phase deadlines and a capped WebAssembly memory declaration. Separate producer and consumer fixtures cover maps, slices, structs, methods, interfaces, generics, package initialization, goroutines, channels, stdin, CGo, C++, and assembly. Go/Plan 9 assembly is still not loaded by upstream TinyGo 0.40.1 and is documented as an upstream limitation rather than emulated by a browser-only subset.

Prepare a verified asset directory, build the runtime, and publish the upstream-only static tree with:

pnpm --dir runtimes/wasm-tinygo prepare:wasm-llvm-upstream -- \
  --compiler /path/to/tinygo-compiler.wasm \
  --root-archive /path/to/tinygoroot.tar.gz \
  --producer-receipt /path/to/producer-receipt.json \
  --package-graph /path/to/tinygo-package-graph.wasm \
  --package-graph-receipt /path/to/package-graph-provider-receipt.json \
  --lld /path/to/lld.wasm \
  --output-dir public/tools/upstream
pnpm --dir runtimes/wasm-tinygo build:upstream
pnpm run sync:wasm-tinygo

PUBLIC_WASM_TINYGO_MODULE_URL or runtimeAssets.tinygo.moduleUrl may point at a separately hosted upstream.js; its sibling chunks and tools/upstream/ assets must be served from the same relative tree. PUBLIC_WASM_TINYGO_APP_URL remains a compatibility alias used only to derive that module URL. Custom hosts may provide runtimeAssets.tinygo.assetLoader, while normal execution and workspace limits continue to apply.

C# / F# / VB.NET / .NET browser integration

The demo app vendors the workspace wasm-dotnet browser module under static/wasm-dotnet/ and exposes C# as CSHARP, F# as FSHARP, and VB.NET as VBNET in the shared playground selector. Refresh the browser module after rebuilding the workspace project with:

pnpm --dir runtimes/wasm-dotnet build
dotnet workload install wasm-tools
dotnet workload install wasm-experimental
pnpm --dir runtimes/wasm-dotnet build:runtime
pnpm run sync:wasm-dotnet

C#, F#, and VB.NET compile in the browser through separate .NET browser-wasm AOT bundles at runtime/csharp/, runtime/fsharp/, and runtime/vbnet/. wasm-idle loads the static wasm-dotnet module only after a .NET language is selected; the module then loads only that language's dotnet.js and filtered shared reference assemblies. No server-side dotnet compile route is involved. For a hosted app, pass runtimeAssets.dotnet.moduleUrl or set PUBLIC_WASM_DOTNET_MODULE_URL. The browser path forwards CLI args and buffered terminal stdin into Console.In. Roslyn C#, FSharp.Compiler.Service, and Roslyn Visual Basic hot paths are selectively AOT compiled in their respective bundles. Monaco diagnostics reuse the selected threaded runtime through an in-process MessageChannel transport because the .NET pthread runtime must start on the browser UI thread.

Browser regression commands

Clean checkouts can prepare the ignored Clang, clangd, and OCaml browser payloads from one receipt-verified manifest:

pnpm run prepare:test-assets -- clangd
pnpm run prepare:test-assets -- clang ocaml

scripts/browser-test-assets.v1.json pins every downloaded file by exact size and SHA-256 digest. The preparer also rejects source or target paths outside their configured roots, validates the final redirect origin, writes atomically, and reuses only matching files. With no group argument, it prepares both the Clang delivery bundle and the complete OCaml browser compiler graph. WASM_IDLE_TEST_ASSET_BASE_URL and WASM_IDLE_TEST_BYPASS_COOKIE can select a compatible mirror and its access cookie.

Browser-level Rust checks are reproducible from this repo:

cd wasm-idle
pnpm run probe:rust-browser
pnpm run test:browser:playwright

WASM_IDLE_BROWSER_URL='http://localhost:5173/absproxy/5173/' \
WASM_IDLE_REUSE_LOCAL_PREVIEW=1 \
pnpm run probe:rust-browser

WASM_IDLE_RUN_REAL_BROWSER_RUST=1 \
WASM_IDLE_BROWSER_URL='http://localhost:5173/absproxy/5173/' \
WASM_IDLE_REUSE_LOCAL_PREVIEW=1 \
pnpm exec vitest run src/lib/playground/rust.playwright.test.ts

The runtime probe exercises the real Chromium page path. The default Rust probe now feeds stdin with a single line (5\n) and expects the page to finish without sending EOF, which keeps the regression aligned with the default Rust sample and proves that pressing Enter is enough for line-based stdin. Programs that intentionally read stdin until EOF can still be finished with Ctrl+D or the toolbar Send EOF button while the process is running. The browser helper writes stdin through the page-owned window.__wasmIdleDebug.writeTerminalInput(...) hook instead of trying to click xterm's hidden helper textarea, which proved too flaky for repeatable Playwright runs. If Rust ever reports invalid metadata files for crate core or Unsupported archive identifier, the browser almost always fetched a stale or wrong wasm-rust sysroot asset. Hard refresh the page and rebuild then resync static/wasm-rust/ from runtimes/wasm-rust/dist/. When browser-rustc does retry, it now emits a visible warning instead of only a debug-level transition into attempt 2/5, 3/5, and so on. When the Rust log option is enabled, those compile-time wasm-rust progress and retry lines are also forwarded into the terminal transcript before the final runtime output, so the browser console is no longer required to inspect build progress. They also resync the vendored wasm-rust bundle and rebuild wasm-idle first, so the browser run is checked against the current assets rather than a stale preview output. The probe/test helper also claims a dedicated local preview port by default instead of reusing whatever already answers on localhost, which keeps the regression target tied to the current build. If you point the probe at dev.seorii.io, remember that route currently requires an authenticated session; the repo-owned regression target is the local preview path above.

Runtime expectations

@wasm-idle/terminal is an optional browser UI package:

pnpm add @wasm-idle/terminal

The root wasm-idle package exports the language runtime and playground binding APIs without installing Svelte or xterm. Browser applications install @wasm-idle/terminal separately and pass it a PlaygroundBinding; Node hosts do not need the package.

@wasm-idle/debug is an optional debugger UI/controller plugin that must be installed separately:

pnpm add @wasm-idle/debug

The root wasm-idle package no longer exports the debug session controller, language adapters, or Monaco integration. Applications that need those APIs import them from @wasm-idle/debug; the Pages application keeps the package as a dev dependency. svelte is a required peer for the reactive controller, while monaco-editor is needed only when using the editor integration.

@wasm-idle/lsp is an optional editor plugin that must be installed separately:

pnpm add @wasm-idle/lsp

Installing the root wasm-idle package does not install @wasm-idle/lsp transitively. Consumers that want browser editor LSP support must add it explicitly, along with the optional provider peers they use.

The wasm-idle, @wasm-idle/debug, @wasm-idle/terminal, @wasm-idle/llvm-core, and @wasm-idle/lsp npm packages contain host/provider JS, types, and lightweight UI/editor-service code, but no compiler or language-runtime payloads. The wasm-llvm repository produces compiler assets but is not an npm runtime dependency. Static compiler/runtime assets are deployed separately and loaded through runtimeAssets HTTP(S) URLs. References to bundled assets below mean files deployed to the page's HTTP origin, not files embedded in an npm package; library consumers must provide their own externally hosted URLs.

Browser runtime payloads stored as .wasm.gz or .tar.gz use the platform DecompressionStream('gzip') path. Zig's standard library is delivered as std.tar.gz, and the Clang and COBOL producer archives are repackaged as .wasm.gz/.tar.gz during sync. fflate remains for user-created workspace ZIP files and legacy external runtime URLs; it is dynamically loaded for compatibility instead of participating in the default runtime path.

@wasm-idle/lsp keeps its host and provider JS in the package. Heavy compiler/runtime modules are external static assets loaded only after LSP is enabled: Python uses pyodide/pyodide.mjs, R uses the versioned webr/<hash>/webr.js, and the AssemblyScript, DuckDB/SQLite SQL, and Ruby providers reuse their static/wasm-*/runtime.mjs trees. Other compiler-backed providers follow the same external URL model through their language-server asset configuration.

Pure-JavaScript provider engines for TypeScript, GraphQL, WAT, and document languages are optional peers of @wasm-idle/lsp, not mandatory production dependencies. The Pages application keeps @wasm-idle/lsp as a dev dependency and dynamically imports each provider only after LSP is enabled and its language is selected. Vite emits those providers into lazy worker chunks, so they are not fetched before they are needed. Library consumers using one of those providers must install its optional peer set, while compiler and language-runtime payloads still come only from external URLs.

Rust still supports an external browser compiler module for library consumers. Point PUBLIC_WASM_RUST_COMPILER_URL at a built wasm-rust ESM entry such as .../wasm-rust/dist/index.js, or pass runtimeAssets.rust.compilerUrl at runtime. Rust source instrumentation is emitted as the separate debug-instrumenter.js static asset and is imported only for debug executions. Override it with runtimeAssets.rust.debugModuleUrl; otherwise wasm-idle resolves it beside the configured compiler module and preserves the compiler URL version query. TinyGo uses the public receipt-verified static/wasm-tinygo/upstream.js compiler by default. Override it with PUBLIC_WASM_TINYGO_MODULE_URL or runtimeAssets.tinygo.moduleUrl; a custom runtimeAssets.tinygo.assetLoader can serve the module's verified sibling toolchain files. The public route supports only wasip1 and rejects unsupported targets instead of selecting the legacy subset. WAT uses the bundled static/wasm-wat/ WABT browser module by default. Override it with PUBLIC_WASM_WAT_MODULE_URL, or pass runtimeAssets.wat.moduleUrl. WASM executes binary WebAssembly modules directly through the browser WebAssembly API. The editor accepts base64, hex, or data:application/wasm content, and the worker connects WASI preview1 stdin/stdout/stderr plus the env.readByte import used by the WAT runner. DuckDB dynamically imports static/wasm-duckdb/runtime.mjs, produced from @duckdb/duckdb-wasm, and opens a fresh in-memory database per run. Override the module with PUBLIC_WASM_DUCKDB_MODULE_URL or runtimeAssets.duckdb.moduleUrl. Workspace files are registered before the active query; terminal input is registered as stdin.txt and /dev/stdin for queries that load it as a file. SQLite dynamically imports static/wasm-sqlite/runtime.mjs, produced from sql.js, and resolves its default sql-wasm.wasm from that static tree. Override the module and optional WASM payload with runtimeAssets.sqlite.moduleUrl/wasmUrl or the corresponding PUBLIC_WASM_SQLITE_MODULE_URL/PUBLIC_WASM_SQLITE_WASM_URL values. PHP dynamically imports the checked-in static/wasm-php/runtime.mjs output from the standalone producers/wasm-php build. That producer pins @php-wasm/web-8-4@3.1.34 and @php-wasm/universal@3.1.34. It always creates PHP 8.4; there is no version field or environment-based version selector. Override only the module location with PUBLIC_WASM_PHP_MODULE_URL or runtimeAssets.php.moduleUrl. A custom host must serve the entry's sibling chunks and assets with compatible CORS and cross-origin isolation headers; a cross-origin host cannot use wasm-idle's same-origin gzip service worker. Bash verifies one unified manifest plus the stored Wasmer SDK JavaScript, Wasmer Wasm, and WEBc before it starts the outer worker. The worker imports only the verified SDK bytes and uses a fixed application-owned nested bootstrap; SDK, worker, Wasm, WEBc, sentinel, and registry network fallbacks are not part of the normal execution path. A rootUrl mirror reuses the bundled profile. Explicit runtimeAssets.bash.baseUrl, manifestUrl, moduleUrl, wasmerWasmUrl, or webcUrl overrides require a complete matching profile and receipts. Arbitrary workerUrl overrides are rejected because executable nested-worker substitution is outside the trust contract. Lua uses the bundled static/wasm-lua/ wasmoon browser module plus its local glue.wasm payload by default. Override it with PUBLIC_WASM_LUA_MODULE_URL, or pass runtimeAssets.lua.moduleUrl. Zig uses the bundled static/wasm-zig/zig_small.wasm compiler and static/wasm-zig/std.tar.gz standard library by default. Override them with PUBLIC_WASM_ZIG_COMPILER_URL and PUBLIC_WASM_ZIG_STDLIB_URL, or pass runtimeAssets.zig.compilerUrl and runtimeAssets.zig.stdlibUrl. The compiler runs under browser WASI, emits a wasm64-wasi artifact with the self-hosted backend, and wasm-idle executes that artifact locally in the worker. Scheme uses the bundled static/wasm-lisp/ Puppy Scheme compiler profile by default. The execution and LSP workers verify its pinned manifest, stored bytes, decompressed size, and logical asset hashes before importing code. A custom profile must provide runtimeAssets.lisp.moduleUrl, manifestUrl, and manifestFingerprint, or the corresponding PUBLIC_WASM_LISP_* variables. Tcl uses the bundled static/wasm-tcl/ Wacl profile by default. The host verifies the manifest and all transport receipts, manually decompresses the canonical .gz.bin assets with exact output limits, and transfers only verified logical bytes to a runner that pins the same manifest fingerprint and closes after one run. URL-only overrides may mirror the bundled bytes. Authorizing different executable bytes requires all Tcl identity fields, manifest and asset receipts, plus the matching workerReceipt in the same runtimeAssets.tcl object; omitted trust fields never fall back to bundled values. The pinned Wacl/RequireJS payload remains trusted executable code: its verified bootstrap needs no follow-up asset fetch, but the worker is not a general network sandbox. Hosts must serve .gz.bin as opaque bytes without Content-Encoding: gzip; legacy .gz aliases are not referenced by the current manifest. Ruby dynamically imports static/wasm-ruby/runtime.mjs, which exposes CRuby 3.4 and its default ruby+stdlib.wasm URL. Override the module or WASM payload with runtimeAssets.ruby.moduleUrl/wasmUrl or PUBLIC_WASM_RUBY_MODULE_URL/ PUBLIC_WASM_RUBY_WASM_URL. AssemblyScript dynamically imports static/wasm-assemblyscript/runtime.mjs, produced from the pinned AssemblyScript compiler and loader. Override it with PUBLIC_WASM_ASSEMBLYSCRIPT_MODULE_URL or runtimeAssets.assemblyscript.moduleUrl. Compilation uses --runtime incremental --bindings raw --optimize --exportRuntime and instantiates the emitted WebAssembly locally. _start or main runs first; otherwise zero-argument numeric, boolean, and string exports are printed to the terminal. AssemblyScript programs can import stdin helpers from env: readLine(): string | null, readAll(): string, and readByte(): i32. readLine waits for Enter-submitted terminal input, while readAll reads until Ctrl+D or the EOF button. WAT modules can import env.readByte(): i32 for byte-oriented stdin; it returns -1 at EOF. Haskell uses the bundled static/wasm-haskell/ ghc-in-browser assets by default. Override them with PUBLIC_WASM_HASKELL_MODULE_URL, PUBLIC_WASM_HASKELL_ROOTFS_URL, and PUBLIC_WASM_HASKELL_BSDTAR_URL, or pass runtimeAssets.haskell. The worker extracts the wasm GHC root filesystem, loads dyld.mjs, and invokes the browser GHC/GHCi entry point locally. Browser stdin is wired into the dyld WASI fd0, so getLine reads terminal input.

The Rust browser path now executes returned artifacts through the target-appropriate runtime inside the Rust worker:

  • wasm32-wasip1 runs as preview1 core wasm through @bjorn3/browser_wasi_shim
  • wasm32-wasip2 runs as a preview2 component through preview2-shim plus transpiled jco output

C-family compilation remains hosted by @wasm-idle/llvm-core, while Rust delegates artifact execution to wasm-rust so the selected target and returned artifact format stay aligned.

Terminal and playground(...).load(...) support either the legacy shared path/rootUrl or per-runtime asset config:

import type { PlaygroundRuntimeAssets } from 'wasm-idle';

const runtimeAssets: PlaygroundRuntimeAssets = {
	rootUrl: 'https://cdn.example.com/repl',
	assemblyscript: {
		moduleUrl: 'https://cdn.example.com/repl/wasm-assemblyscript/runtime.mjs'
	},
	duckdb: {
		moduleUrl: 'https://cdn.example.com/repl/wasm-duckdb/runtime.mjs'
	},
	php: {
		moduleUrl: 'https://cdn.example.com/repl/wasm-php/runtime.mjs'
	},
	ruby: {
		moduleUrl: 'https://cdn.example.com/repl/wasm-ruby/runtime.mjs'
	},
	sqlite: {
		moduleUrl: 'https://cdn.example.com/repl/wasm-sqlite/runtime.mjs'
	},
	python: {
		loader: async ({ asset }) => ({ url: `https://cdn.example.com/repl/pyodide/${asset}` })
	},
	r: {
		baseUrl: 'https://cdn.example.com/repl/webr/<asset-version>/'
	},
	java: {
		baseUrl: 'https://cdn.example.com/repl/teavm/'
	},
	clang: {
		loader: async ({ asset }) => ({ url: `https://cdn.example.com/repl/clang/${asset}` })
	},
	clangd: {
		loader: async ({ asset }) => ({ url: `https://cdn.example.com/repl/clangd/${asset}` })
	},
	rust: {
		compilerUrl: 'https://cdn.example.com/wasm-rust/index.js'
	},
	dotnet: {
		moduleUrl: 'https://cdn.example.com/wasm-dotnet/index.js'
	},
	wat: {
		moduleUrl: 'https://cdn.example.com/wasm-wat/index.js'
	},
	lua: {
		moduleUrl: 'https://cdn.example.com/wasm-lua/index.js'
	},
	zig: {
		compilerUrl: 'https://cdn.example.com/wasm-zig/zig_small.wasm',
		stdlibUrl: 'https://cdn.example.com/wasm-zig/std.tar.gz'
	},
	lisp: {
		moduleUrl: 'https://cdn.example.com/wasm-lisp/index.js'
	},
	haskell: {
		moduleUrl: 'https://cdn.example.com/wasm-haskell/dyld.mjs',
		rootfsUrl: 'https://cdn.example.com/wasm-haskell/rootfs.tar.zst',
		bsdtarUrl: 'https://cdn.example.com/wasm-haskell/bsdtar.wasm'
	},
	nim: {
		baseUrl: 'https://cdn.example.com/wasm-nim/',
		workerUrl: 'https://cdn.example.com/wasm-nim/runner-worker.js'
	}
};

Static module overrides such as PHP's moduleUrl identify an entry module, not a self-contained file. Mirror its complete sibling asset tree at the same relative paths. Cross-origin asset hosts must provide compatible CORS and COEP/CORP headers and cannot rely on wasm-idle's same-origin gzip service worker.

Verified static runtimes such as Janet and Julia intentionally omit URL-only examples: a custom baseUrl, manifestUrl, or workerUrl must be accompanied by every identity and asset-receipt field declared by that runtime's asset config, including the matching workerReceipt. Partial trust bundles fail closed instead of borrowing receipts from bundled executable bytes.

Python custom loaders receive file names under the Pyodide asset root and can serve both core assets and package files. TeaVM custom loaders receive file names under the TeaVM asset root. Clang custom loaders receive bin/memfs.wasm.gz, bin/clang.wasm.gz, bin/lld.wasm.gz, and bin/sysroot.tar.gz; COBOL loaders receive cobc.wasm.gz, rootfs.tar.gz, and c-sysroot.tar.gz. The shared loader pipes these gzip response bodies through native DecompressionStream. Legacy external manifests that still reference ZIP assets remain supported through the dynamically loaded fflate compatibility path. Zig custom loaders receive zig_small.wasm and std.tar.gz; an explicitly configured legacy std.zip URL remains compatible. Clangd custom loaders receive clangd.js and clangd.wasm.gz, with the worker decompressing the gzip payload before instantiation. Rust expects a browser-loadable compiler module URL; that module is responsible for serving its own nested runtime assets. C#, F#, and VB.NET expect a browser-loadable wasm-dotnet module with its language-specific static .NET browser-wasm runtime assets. Compressed TeaVM runtime assets are no longer unpacked inside the library; provide the final file URL or handle decompression in your own loader.

To reuse the same runtime asset configuration for both <Terminal> and direct playground(...) access, bind it once:

import Terminal from '@wasm-idle/terminal';
import { createPlaygroundBinding } from 'wasm-idle';

const wasmIdle = createPlaygroundBinding({
	rootUrl: 'https://cdn.example.com/repl',
	rust: {
		compilerUrl: 'https://cdn.example.com/wasm-rust/index.js'
	},
	dotnet: {
		moduleUrl: 'https://cdn.example.com/wasm-dotnet/index.js'
	}
});

const sandbox = await wasmIdle.load('PYTHON');
await sandbox.load('print("hi")', false);
<Terminal {...wasmIdle.terminalProps} bind:terminal />

Compiler assets produced by wasm-llvm are deployed to external static hosting and loaded by @wasm-idle/llvm-core. Also powered by Pyodide, TeaVM, wasm-rust, wasm-dotnet, wasm-of-js-of-ocaml, wasm-typescript, wasm-lisp, wasm-wat, wasm-lua, wasm-zig, CBQN, Janet, AtomVM/Popcorn, and ghc-in-browser.