Lock a file before editing
AI agents use announce_file_change to create or update resources in A2AMCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your A2AMCP environment.
The tool locks a file before editing, which is a write/coordination operation that modifies shared state in the Redis-backed coordination system. It creates a lock record to prevent conflicts. The description is somewhat inconsistent with the name (announcing a change vs. locking), which lowers confidence slightly.
From the tool's definition Tool name: 'announce_file_change'; description: 'Lock a file before editing'
Documented attack patterns abuse exactly the kind of access announce_file_change gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and A2AMCP, and nothing reaches the server without passing your rules. This is the rule we recommend for announce_file_change:
{
"version": "1",
"default": "deny",
"tools": {
"announce_file_change": {
"limits": [
{
"counter": "announce_file_change_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}announce_file_change 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.
Free to start. No card required.
Lock a file before editing. It is categorised as a Write tool in the A2AMCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the A2A MCP server in PolicyLayer and add a rule for announce_file_change: 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 A2AMCP. Nothing to install.
announce_file_change 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 announce_file_change 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 announce_file_change. 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.
announce_file_change is provided by the A2A MCP server (webdevtodayjason/a2amcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from A2AMCP, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
17 A2AMCP tools catalogued and risk-classified — across an index of 43,000+ MCP servers.