MCP Blast-Radius Auditor

Catch an MCP server that touches files it said it wouldn't — and block the merge in CI.

Statically extract what a third-party MCP server can actually reach (files, network, subprocess, env) and compare against declared boundaries when a manifest is present.

30-second scan

pipx run mcp-blast-radius  # MCP server
pip install . && mcp-blast-radius-gate --gate-mode blocking --target-dir /path/to/mcp-server

• Red (blocking): divergence detected — code touches paths or capabilities not declared in manifest.
• Green: no divergences (or no manifest — blast radius report only, advisory pass).

Install

pip install mcp-blast-radius==0.2.0

Or from source:

python3 -m venv .venv
source .venv/bin/activate
pip install .

AOS zone semantics: aos-standard/AOS-spec.

CLI entry

mcp-blast-radius          # MCP stdio server
mcp-blast-radius-gate     # CI gate (default blocking, exit 1 on fail)

CI blocking gate

mcp-blast-radius-gate --gate-mode blocking --target-dir .
# no divergences → exit 0 / divergences or declaration violations → exit 1

MCP tools

• aos_compliance_validate — scan one MCP server directory (target_dir required; tool_id optional label)
• aos_compliance_self_test — wiring smoke test

Default gate_mode=advisory. Use gate_mode=blocking in CI to fail on divergences.

What is extracted

Layer	Scope	Confidence
Dependencies	requirements.txt, pyproject.toml, package.json	declared
Python AST	imports, file I/O, network, env, subprocess; MCP tool attribution	observed-static / cannot-determine
Divergence	manifest permitted_output_paths / oracle_paths vs observed access	blocking when mismatch

Limitations: Static analysis only. Dynamic imports, getattr/eval, obfuscation, and native extensions may hide capabilities. We do not claim complete coverage — every finding includes a confidence label.

Environment

Variable	Purpose
AOS_VALIDATOR_TARGET_DIR	Default scan root when target_dir is omitted
AOS_VALIDATOR_MCP_LOG	JSONL path for local tool call log (never sent externally)
AOS_VALIDATOR_CALLER	Caller label (ci, smoke_self_call, etc.)

Example

aos_compliance_validate target_dir=/path/to/my-mcp-server gate_mode=blocking

License

MIT