biome-format

Formats files with Biome (format --write) and returns a structured list of changed files.

SERVERGithub SOURCE@paretools/github

Medium RISK CLASS

Category Write

Parameters 00 required

Recommended Rate-limitedsee the rule below

Registry record Grade F, identity unverified Pull the record →

This record as markdown: /tools/io-github-dave-london-github/biome-format.md

WHAT IT DOES

What biome-format does on Github

AI agents use biome-format to create or update resources in Github, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Github environment.

RISK

Why biome-format is rated Medium

This tool modifies files on the filesystem by applying code formatting via Biome. While formatting changes are typically reversible (the original code is still in version control or backups), the tool directly overwrites file contents. This is a Write operation rather than Destructive because formatting is generally reversible and doesn't permanently destroy data.

From the tool's definition Tool description states 'Formats files with Biome (format --write)' which modifies files in place using the --write flag, and 'returns a structured list of changed files' confirming write operations occur.

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs biome-format safely

PolicyLayer is an MCP gateway: it sits between your AI agents and Github, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For biome-format, this is the rule to start with:

biome-format Rate-limited

biome-format stays usable, but capped: an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "biome-format": {
      "limits": [
        {
          "counter": "biome-format_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect Github, apply this rule, and every biome-format call is checked against it from then on.

FAQ

Questions about biome-format

What does the biome-format tool do? +

Formats files with Biome (format --write) and returns a structured list of changed files. It is categorised as a Write tool in the Github MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on biome-format? +

Register the Github MCP server in PolicyLayer and add a rule for biome-format: 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 Github. Nothing to install.

What risk level is biome-format? +

biome-format is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit biome-format? +

Yes. Add a rate_limit block to the biome-format 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.

How do I block biome-format completely? +

Set action: deny in the PolicyLayer policy for biome-format. 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.

What MCP server provides biome-format? +

biome-format is provided by the Github MCP server (@paretools/github). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

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