lock_file
Acquire an exclusive lock on a file path. Throws if another agent holds an active lock. Same agent re-locks refreshes the TTL.
This record as markdown: /tools/todos/lock-file.md
What lock_file does on Todos
AI agents use lock_file to create or update resources in Todos, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Todos environment.
Why lock_file is rated Medium
This tool acquires a lock on a file path, which is a write-like operation that modifies system state (lock metadata) and can block other agents from accessing the file. It is reversible (locks expire via TTL or can be released), so it doesn't qualify as Destructive. The blast radius is medium because misuse could cause deadlocks or denial-of-service for other agents trying to access the file.
From the tool's definition Acquire an exclusive lock on a file path. Throws if another agent holds an active lock. Same agent re-locks refreshes the TTL.
Attacks that exploit this kind of access
The rule that runs lock_file safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Todos, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For lock_file, this is the rule to start with:
lock_file 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 Todos, apply this rule, and every lock_file call is checked against it from then on.
Questions about lock_file
Acquire an exclusive lock on a file path. Throws if another agent holds an active lock. Same agent re-locks refreshes the TTL. It is categorised as a Write tool in the Todos MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Todos MCP server in PolicyLayer and add a rule for lock_file: 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 Todos. Nothing to install.
lock_file 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 lock_file 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 lock_file. 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.
lock_file is provided by the Todos MCP server (@hasna/todos). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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