sponsio-claude-code

sponsio-claude-code (Claude Code plugin)

A Claude Code plugin that guards every PreToolUse event in your session against per-plugin Sponsio contract libraries.

Just want to install + use it? See QUICKSTART.md. The README below is the architecture / internals reference.

Note on trace-aware contracts. Argument-level contracts (scope_limit, arg_blacklist, arg_value_range, dangerous_bash_commands, …) fire on every hook today. Trace-aware contracts (must_precede, rate_limit, cooldown) require cross-call session state and land with daemon mode; the stateless hook can't see them on its own.

Architecture (Mode A — host-installed plugin)

PreToolUse fires → Claude Code spawns `sponsio plugin guard --stdin`
                 → stdin: {"tool_name": "...", "tool_input": {...}, ...}
                 → derive plugin id from tool_name
                       Bash, Edit, Write, …      → "_host"
                       acme:fetch_data           → "acme"
                       mcp__acme__fetch          → "acme"
                 → load ~/.sponsio/plugins/<plugin>/sponsio.yaml
                 → guard.guard_before(tool_name, tool_input)
                 → emit deny JSON or exit 0 silently

Each plugin gets its own contract library so:

• the user can ship official + community + private libraries side by side
• installing/uninstalling a plugin doesn't churn an unrelated library
• evaluation is fast — only one plugin's rules run per tool call

Install (development)

# 1. Install Sponsio so `sponsio plugin guard --stdin` is on PATH.
pip install -e .

# 2. Bootstrap the per-plugin library tree (creates ~/.sponsio/plugins/_host/
#    and runs an allow + block smoke test).
sponsio plugin init

# 3. (Optional) Drop in starter libraries for popular MCP servers.
sponsio plugin install --list                  # see what's bundled
sponsio plugin install github filesystem playwright

# 4. Load the plugin into Claude Code.
claude --plugin-dir ./plugins/sponsio-claude-code

plugin init ships the same default _host library as the libraries/_host/sponsio.yaml in this directory — pick whichever install path is more convenient.

Starter libraries shipped today

Routing key	Source MCP server	Highlights
_host	Claude Code built-ins (Bash, Edit, …)	rm -rf /, fork bombs, curl | bash, line-continuation evasion, reverse shells
github	github/github-mcp-server	hard-deny on delete_repository, protected-branch deletes blocked, dotenv / workflow-yaml writes blocked, issue / PR / merge rate caps
filesystem	@modelcontextprotocol/server-filesystem	dotenv / SSH / AWS / /etc / launchd path blacklist on read + write + edit + move
playwright	microsoft/playwright-mcp	navigation blacklist (localhost / RFC1918 / file:// / javascript:), browser_evaluate cookie / fetch / sendBeacon exfil block, credit-card-shape typing block

To generate a starter library for an unbundled plugin from its manifest + tool list:

sponsio plugin scan ./path/to/some-plugin --tools tool_a,tool_b --apply

Verifying it works without Claude Code

The hook contract is just JSON-on-stdin → JSON-on-stdout, so you can exercise it with echo:

# Allowed — exit 0, no stdout
echo '{"hook_event_name":"PreToolUse","tool_name":"Bash","tool_input":{"command":"ls"}}' \
  | sponsio plugin guard --stdin

# Blocked — JSON deny on stdout
echo '{"hook_event_name":"PreToolUse","tool_name":"Bash","tool_input":{"command":"rm -rf /"}}' \
  | sponsio plugin guard --stdin
# {"hookSpecificOutput": {"hookEventName": "PreToolUse",
#                         "permissionDecision": "deny",
#                         "permissionDecisionReason": "..."}}

Layout

sponsio-claude-code/
├── .claude-plugin/
│   └── plugin.json              # required Claude Code manifest
├── hooks/
│   └── hooks.json               # PreToolUse → `sponsio plugin guard --stdin`
├── libraries/
│   ├── _host/sponsio.yaml       # Claude Code built-in tools (Bash, Edit, …)
│   ├── github/sponsio.yaml      # mcp__github__* — github-mcp-server
│   ├── filesystem/sponsio.yaml  # mcp__filesystem__* — server-filesystem
│   └── playwright/sponsio.yaml  # mcp__playwright__* — playwright-mcp
└── README.md

These are mirror copies of the bundled package data under sponsio/plugin/defaults/*.yaml — one is for --plugin-dir users (cp from this directory), the other for pip-install users (via sponsio plugin install). A test enforces byte-equality.

Adding rules for a specific plugin

mkdir -p ~/.sponsio/plugins/acme
cat > ~/.sponsio/plugins/acme/sponsio.yaml <<'YAML'
version: "1"
agents:
  acme:
    contracts:
      - desc: "mcp__acme__fetch may not call internal hosts"
        G:
          pattern: arg_blacklist
          args: [mcp__acme__fetch, url, ["^https?://(localhost|10\\.|192\\.168\\.)"]]
YAML

Known gaps (planned)

Gap	Status
Trace-aware contracts (must_precede, rate_limit)	Need daemon mode for per-session state
sponsio plugin scan over a Claude Code plugin manifest	Stage 2
Hot-load library updates without /reload-plugins	TBD
Claude Code namespaced-skill names (my-plugin:hello)	Grounding bug — Stage 2