Write content to any file on the local filesystem
Risk signalsAccepts file system path (path) · Accepts raw HTML/template content (content)
Part of the Faf server.
Free to start. No card required.
AI agents use faf_write to create or modify resources in Faf. Write operations carry medium risk because an autonomous agent could trigger bulk unintended modifications. Rate limits prevent a single agent session from making hundreds of changes in rapid succession. Argument validation ensures the agent passes expected values.
Without a policy, an AI agent could call faf_write repeatedly, creating or modifying resources faster than any human could review. PolicyLayer's rate limiting ensures write operations happen at a controlled pace, and argument validation catches malformed or unexpected inputs before they reach Faf.
Write tools can modify data. A rate limit prevents runaway bulk operations from AI agents.
{
"version": "1",
"default": "deny",
"tools": {
"faf_write": {
"limits": [
{
"counter": "faf_write_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}See the full Faf policy for all 32 tools.
These attack patterns abuse exactly the kind of access faf_write gives an agent. Each links to the full case and the policy that stops it:
Other write tools across the catalogue. The same approach applies to each: rate-limit and validate the arguments.
Write content to any file on the local filesystem. It is categorised as a Write tool in the Faf MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Faf MCP server in PolicyLayer and add a rule for faf_write: 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 Faf. Nothing to install.
faf_write 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 faf_write 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 faf_write. 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.
faf_write is provided by the Faf MCP server (faf-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 32 Faf tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
4,600+ MCP servers and 31,000+ tools scanned and risk-classified.