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Default strict_mcp_config to true #1148

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9 changes: 9 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -184,6 +184,15 @@ options = ClaudeAgentOptions(
)
```

By default, the SDK uses only the MCP servers supplied through `mcp_servers`.
It does not implicitly load project `.mcp.json`, user/global settings, or
plugin-provided MCP servers. Applications that intentionally rely on Claude
Code's ambient MCP discovery can restore that behavior explicitly:

```python
options = ClaudeAgentOptions(strict_mcp_config=False)
```

### Hooks

A **hook** is a Python function that the Claude Code _application_ (_not_ Claude) invokes at specific points of the Claude agent loop. Hooks can provide deterministic processing and automated feedback for Claude. Read more in [Intercept and control agent behavior with hooks](https://platform.claude.com/docs/en/agent-sdk/hooks).
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5 changes: 4 additions & 1 deletion src/claude_agent_sdk/types.py
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Expand Up @@ -1800,10 +1800,13 @@ class ClaudeAgentOptions:
to an MCP config JSON file.
"""

strict_mcp_config: bool = False
strict_mcp_config: bool = True
"""When ``True``, only use MCP servers passed via :attr:`mcp_servers`,
ignoring all other MCP configurations the CLI would otherwise load (e.g.
project ``.mcp.json``, user/global settings, plugin-provided servers).
Defaults to ``True`` so SDK applications do not implicitly execute MCP
servers discovered from their working directory. Set this to ``False`` to
retain Claude Code's ambient MCP discovery behavior.
Maps to the CLI's ``--strict-mcp-config`` flag and matches the TypeScript
SDK's ``strictMcpConfig`` option."""

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10 changes: 5 additions & 5 deletions tests/test_transport.py
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Expand Up @@ -92,13 +92,13 @@ def test_build_command_include_hook_events(self):
assert "--include-hook-events" not in cmd_off

def test_build_command_strict_mcp_config(self):
"""Test that --strict-mcp-config is emitted only when enabled."""
transport = SubprocessCLITransport(
prompt="test", options=make_options(strict_mcp_config=True)
)
"""Test strict MCP isolation is the default and can be disabled."""
transport = SubprocessCLITransport(prompt="test", options=make_options())
assert "--strict-mcp-config" in transport._build_command()

transport = SubprocessCLITransport(prompt="test", options=make_options())
transport = SubprocessCLITransport(
prompt="test", options=make_options(strict_mcp_config=False)
)
assert "--strict-mcp-config" not in transport._build_command()

def test_build_command_resume_and_session_id(self):
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