diff --git a/src/brigade/agents.py b/src/brigade/agents.py
index 5f7d186a..71c3c355 100644
--- a/src/brigade/agents.py
+++ b/src/brigade/agents.py
@@ -79,7 +79,12 @@ class _GrokFinal:
 # leave them available). Read-only is also enforced by `--permission-mode plan`,
 # the actual permission/sandbox mechanism, so a buggy `--disallowedTools` for
 # MCP tools cannot let a write through.
-_CLAUDE_DISALLOWED_READ_ONLY = "Task,Agent,Bash,Edit,Write,NotebookEdit,mcp__*"
+# `WebSearch`/`WebFetch` (Claude Code's built-in web tool names) are denied too:
+# they are read tools, but under `--permission-mode plan` they still route to an
+# interactive approval prompt that a non-interactive Brigade worker cannot
+# answer, so the worker blocks with no final output (#456). Hiding them from the
+# tool surface, exactly like Bash/Edit/Write, removes the prompt entirely.
+_CLAUDE_DISALLOWED_READ_ONLY = "Task,Agent,Bash,Edit,Write,NotebookEdit,WebSearch,WebFetch,mcp__*"
 
 
 class UnsupportedSandboxError(ValueError):
diff --git a/tests/test_agents.py b/tests/test_agents.py
index a793eb1b..5e762c68 100644
--- a/tests/test_agents.py
+++ b/tests/test_agents.py
@@ -59,7 +59,7 @@ def test_build_argv_for_read_only_codex():
         "--permission-mode",
         "plan",
         "--disallowedTools",
-        "Task,Agent,Bash,Edit,Write,NotebookEdit,mcp__*",
+        "Task,Agent,Bash,Edit,Write,NotebookEdit,WebSearch,WebFetch,mcp__*",
         "--",
         "hi",
     ]
@@ -124,7 +124,7 @@ def test_claude_read_only_disallows_mutating_tools_and_subagents():
         "--permission-mode",
         "plan",
         "--disallowedTools",
-        "Task,Agent,Bash,Edit,Write,NotebookEdit,mcp__*",
+        "Task,Agent,Bash,Edit,Write,NotebookEdit,WebSearch,WebFetch,mcp__*",
         "--",
         "inspect it",
     ]
@@ -137,7 +137,7 @@ def test_claude_read_only_sandbox_variant_matches_read_only_flag():
         "--permission-mode",
         "plan",
         "--disallowedTools",
-        "Task,Agent,Bash,Edit,Write,NotebookEdit,mcp__*",
+        "Task,Agent,Bash,Edit,Write,NotebookEdit,WebSearch,WebFetch,mcp__*",
         "--",
         "inspect it",
     ]
@@ -199,6 +199,33 @@ def test_claude_danger_full_access_prompt_is_not_consumed_by_disallowed_tools():
     assert "--dangerously-skip-permissions" in argv
 
 
+def test_claude_read_only_denies_web_tools_that_prompt_for_approval():
+    # Regression for #456: under `--permission-mode plan`, Claude Code's built-in
+    # WebSearch/WebFetch tools route to an interactive approval prompt that a
+    # non-interactive Brigade worker cannot answer, so a read-only worker blocked
+    # with no final output. Both must be hidden from the read-only tool surface
+    # via the deny list, exactly like Bash/Edit/Write.
+    prompt = "summarize this module"
+    argv = agents.build_argv("claude", prompt, read_only=True)
+
+    disallowed_index = argv.index("--disallowedTools")
+    denied = argv[disallowed_index + 1].split(",")
+    assert "WebSearch" in denied
+    assert "WebFetch" in denied
+    # The deny list is still a single comma-joined argv element and the prompt
+    # is still separated by the end-of-options marker (#446/#451 must not
+    # regress): the web tool names must not leak into the prompt position.
+    assert argv[disallowed_index + 2] == "--"
+    assert argv[-1] == prompt
+    # The danger-full-access branch skips permissions entirely, so no prompt
+    # can block there; its deny list stays scoped to subagent spawning only.
+    full_access = agents.build_argv("claude", prompt, sandbox="danger-full-access")
+    full_denied = full_access[full_access.index("--disallowedTools") + 1]
+    assert full_denied == agents._CLAUDE_DISALLOWED_ALWAYS
+    assert "WebSearch" not in full_denied
+    assert "WebFetch" not in full_denied
+
+
 def test_claude_workspace_write_rejected_before_launch():
     # Contract: workspace-write cannot be truthfully enforced by this CLI
     # version, so it is rejected before launch with an actionable error.