black
Runs Black code formatter and returns structured results (files changed, unchanged, would reformat).
This record as markdown: /tools/io-github-dave-london-pare-python/black.md
What black does on Python
AI agents call black to retrieve information from Python without modifying anything. It is typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
| Parameter | Type | Required | Description |
|---|---|---|---|
diff | boolean | — | Show diff of changes without applying (--diff) |
path | string | — | Project root path |
check | boolean | — | Check mode (report without modifying files) |
config | string | — | Path to explicit Black config file (--config) |
compact | boolean | — | Prefer compact output |
preview | boolean | — | Enable preview style (--preview) |
targets | array | — | Files or directories to format (default: ["."]) |
lineLength | integer | — | Override the configured line length (--line-length) |
targetVersion | string | — | Python version to target, e.g. 'py310', 'py311', 'py312' (--target-version) |
skipStringNormalization | boolean | — | Skip string quote normalization (-S) |
Parameters from the server's own tool schema.
Why black is rated Low
Even though black only reads data, uncontrolled read access leaks sensitive information and racks up API costs: an agent caught in a retry loop can make thousands of calls a minute without anyone noticing.
Risk signalsAccepts file system path (path) · High parameter count (10 properties)
Attacks that exploit this kind of access
The rule that runs black safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Python, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For black, this is the rule to start with:
black 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 Python, apply this rule, and every black call is checked against it from then on.
Questions about black
Runs Black code formatter and returns structured results (files changed, unchanged, would reformat). It is categorised as a Read tool in the Python MCP Server, which means it retrieves data without modifying state.
black accepts 10 parameters: diff, path, check, config, compact, preview, targets, lineLength, targetVersion, skipStringNormalization. The full parameter table on this page comes from the server's own tool schema.
Register the Python MCP server in PolicyLayer and add a rule for black: 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 Python. Nothing to install.
black 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 black 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 black. 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.
black is provided by the Python 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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