AI agents call estimate_file_coverage to retrieve information from Simplecov without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool reads existing SimpleCov coverage data and performs computational estimation/analysis to predict coverage outcomes. It does not execute tests, modify coverage data, create or delete files, or trigger any side effects. It is purely analytical in nature, similar to the other sibling tools (get_file_coverage, get_summary, get_uncovered_lines, list_files) which are all Read operations.
From the tool's definition Tool description states it 'estimates file coverage after changes' and 'estimates the impact of code changes on coverage without re-running tests' — it performs analysis and prediction without executing tests, modifying data, or triggering external operations.
Attacks that exploit this kind of access
ファイル変更後のカバレッジを推定する。テスト再実行なしで、コード変更がカバレッジに与える影響を見積もる。. It is categorised as a Read tool in the Simplecov MCP Server, which means it retrieves data without modifying state.
Register the Simplecov MCP server in PolicyLayer and add a rule for estimate_file_coverage: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Simplecov. Nothing to install.
estimate_file_coverage is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the estimate_file_coverage rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for estimate_file_coverage. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
estimate_file_coverage is provided by the Simplecov MCP server (ryo-ymd/simplecov-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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