biome-format
Formats files with Biome (format --write) and returns a structured list of changed files.
This record as markdown: /tools/io-github-dave-london-cargo/biome-format.md
What biome-format does on Cargo
AI agents use biome-format to create or update resources in Cargo, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Cargo environment.
Why biome-format is rated Medium
This tool modifies files reversibly by reformatting them. It is a Write operation because it creates or modifies data (file contents) reversibly—formatting changes can be undone by reverting to version control or re-running with different settings. It does not execute arbitrary code, delete data, or cause financial impact.
From the tool's definition Tool description states 'Formats files with Biome (format --write) and returns a structured list of changed files.' The --write flag indicates files are modified in place.
Attacks that exploit this kind of access
The rule that runs biome-format safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Cargo, 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 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.
The button opens the PolicyLayer dashboard: create your workspace, connect Cargo, apply this rule, and every biome-format call is checked against it from then on.
Questions about biome-format
Formats files with Biome (format --write) and returns a structured list of changed files. It is categorised as a Write tool in the Cargo MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Cargo 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 Cargo. Nothing to install.
biome-format is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
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.
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.
biome-format is provided by the Cargo 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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