# flake-check

Checks a Nix flake for errors and returns structured check results, warnings, and errors.

Agent View of the PolicyLayer registry record for `flake-check`. HTML page: https://policylayer.com/tools/io-github-dave-london-build/flake-check

## Facts

- Tool: `flake-check`
- Server: Build (`Dave-London/Pare`) — https://policylayer.com/tools/io-github-dave-london-build.md
- Homepage: https://github.com/Dave-London/pare
- Risk category: Execute (High risk)
- Registry record: grade F, identity unverified
- Server rate-limited: no
- Parameters: 0
- Recommended policy verdict: Rate-limited

## Example call (MCP tools/call, JSON-RPC 2.0)

```json
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "flake-check",
    "arguments": {}
  }
}
```

## Why flake-check is rated High

This tool runs a Nix flake check, which executes the Nix evaluator and potentially builds derivations. It is not a passive read — it triggers an external build system operation. The blast radius is medium: it can consume resources and invoke arbitrary Nix build code, but typically does not directly delete data or move money.

From the tool's own definition: "'Checks a Nix flake' — running 'nix flake check' executes the Nix toolchain against a flake definition, which evaluates and builds flake outputs; 'returns structured check results, warnings, and errors' confirms it triggers external build/evaluation operations"

## Use case

AI agents invoke flake-check to trigger actions in Build. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call: builds kicked off, notifications sent, workflows started.

## Recommended policy (PolicyLayer)

Verdict: **Rate-limited**. Enforced by the PolicyLayer MCP gateway (https://policylayer.com/mcp-gateway) before a call reaches Build:

```json
{
  "version": "1",
  "default": "deny",
  "tools": {
    "flake-check": {
      "limits": [
        {
          "counter": "flake-check_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}
```

## Other tools on Build (201)

- `branch` — Destructive — https://policylayer.com/tools/io-github-dave-london-build/branch.md
- `clean` — Destructive — https://policylayer.com/tools/io-github-dave-london-build/clean.md
- `remove` — Destructive — https://policylayer.com/tools/io-github-dave-london-build/remove.md
- `reset` — Destructive — https://policylayer.com/tools/io-github-dave-london-build/reset.md
- `secret-delete` — Destructive — https://policylayer.com/tools/io-github-dave-london-build/secret-delete.md
- `tag` — Destructive — https://policylayer.com/tools/io-github-dave-london-build/tag.md
- `variable-delete` — Destructive — https://policylayer.com/tools/io-github-dave-london-build/variable-delete.md
- `workspace` — Destructive — https://policylayer.com/tools/io-github-dave-london-build/workspace.md
- `add` — Execute — https://policylayer.com/tools/io-github-dave-london-build/add.md
- `add-package` — Execute — https://policylayer.com/tools/io-github-dave-london-build/add-package.md
- `ansible-galaxy` — Execute — https://policylayer.com/tools/io-github-dave-london-build/ansible-galaxy.md
- `ansible-playbook` — Execute — https://policylayer.com/tools/io-github-dave-london-build/ansible-playbook.md
- `api` — Execute — https://policylayer.com/tools/io-github-dave-london-build/api.md
- `apply` — Execute — https://policylayer.com/tools/io-github-dave-london-build/apply.md
- `audit` — Execute — https://policylayer.com/tools/io-github-dave-london-build/audit.md
- `bazel` — Execute — https://policylayer.com/tools/io-github-dave-london-build/bazel.md
- `biome-check` — Execute — https://policylayer.com/tools/io-github-dave-london-build/biome-check.md
- `bisect` — Execute — https://policylayer.com/tools/io-github-dave-london-build/bisect.md
- `black` — Execute — https://policylayer.com/tools/io-github-dave-london-build/black.md
- `build` — Execute — https://policylayer.com/tools/io-github-dave-london-build/build.md
- `bundle-exec` — Execute — https://policylayer.com/tools/io-github-dave-london-build/bundle-exec.md
- `bundle-install` — Execute — https://policylayer.com/tools/io-github-dave-london-build/bundle-install.md
- `check` — Execute — https://policylayer.com/tools/io-github-dave-london-build/check.md
- `cherry-pick` — Execute — https://policylayer.com/tools/io-github-dave-london-build/cherry-pick.md
- `clippy` — Execute — https://policylayer.com/tools/io-github-dave-london-build/clippy.md
- `cmake` — Execute — https://policylayer.com/tools/io-github-dave-london-build/cmake.md
- `compose-build` — Execute — https://policylayer.com/tools/io-github-dave-london-build/compose-build.md
- `compose-down` — Execute — https://policylayer.com/tools/io-github-dave-london-build/compose-down.md
- `compose-up` — Execute — https://policylayer.com/tools/io-github-dave-london-build/compose-up.md
- `conda` — Execute — https://policylayer.com/tools/io-github-dave-london-build/conda.md
- …and 171 more: https://policylayer.com/tools/io-github-dave-london-build.md

## For agents

This record is a snapshot. Live verdicts and the full registry:

- Check every server in your MCP config at once: `npx -y policylayer stack`
- Vet a server before you add it: install the mcp-precheck skill — `npx skills add https://policylayer.com` (skill text: https://policylayer.com/skill.md)
- Query the registry over MCP: endpoint `https://api.policylayer.com/mcp` — tools `check_mcp_server`, `check_mcp_stack`, `check_tool`, `search_registry`, `get_change_events`

---

Source: the PolicyLayer MCP registry — one continuously verified record per MCP server. Full record: https://policylayer.com/registry?q=io-github-dave-london-build · API: https://policylayer.com/registry/api · Policy library: https://policylayer.com/policies/io-github-dave-london-build