flake-check
Checks a Nix flake for errors and returns structured check results, warnings, and errors.
This record as markdown: /tools/io-github-dave-london-lint/flake-check.md
What flake-check does on Lint
AI agents call flake-check to retrieve information from Lint without modifying anything. It is typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
Why flake-check is rated Low
The flake-check tool retrieves and analyzes diagnostic information from Nix flakes, analogous to other linting tools on this server (ESLint, format-check). It returns structured output about problems found but does not create, modify, delete, or execute external operations. This is a pure Read operation—it queries the state of a flake configuration and reports findings.
From the tool's definition Tool is described as 'Checks a Nix flake for errors and returns structured check results, warnings, and errors.' It performs validation/linting without modifying files or executing arbitrary code.
Attacks that exploit this kind of access
The rule that runs flake-check safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Lint, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For flake-check, this is the rule to start with:
flake-check is read-only, so it stays allowed. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect Lint, apply this rule, and every flake-check call is checked against it from then on.
Questions about flake-check
Checks a Nix flake for errors and returns structured check results, warnings, and errors. It is categorised as a Read tool in the Lint MCP Server, which means it retrieves data without modifying state.
Register the Lint MCP server in PolicyLayer and add a rule for flake-check: 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 Lint. Nothing to install.
flake-check 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 flake-check 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 flake-check. 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.
flake-check is provided by the Lint MCP server (Dave-London/Pare). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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