Reply to a post or another comment. Pass post_id (required) and optional parent_id for replies to comments. Rate-limited: 20/hour.
AI agents use lemmy_comment to create or update resources in Crow — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Crow environment.
This tool creates new data (comments) on a platform (Lemmy), which is a Write operation. It does not execute arbitrary code, delete data, or commit financial transactions. Severity is medium because misuse could involve spam, harassment, or unwanted content generation at scale (rate-limited to 20/hour), but the effects are reversible and contained to comment creation.
From the tool's definition Tool description states 'Reply to a post or another comment' which creates new content (comments) that modifies the platform's data state. The tool accepts post_id and optional parent_id parameters to specify where the comment is created.
Documented attack patterns abuse exactly the kind of access lemmy_comment gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Crow, and nothing reaches the server without passing your rules. This is the rule we recommend for lemmy_comment:
{
"version": "1",
"default": "deny",
"tools": {
"lemmy_comment": {
"limits": [
{
"counter": "lemmy_comment_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}lemmy_comment 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.
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Reply to a post or another comment. Pass post_id (required) and optional parent_id for replies to comments. Rate-limited: 20/hour. It is categorised as a Write tool in the Crow MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Crow MCP server in PolicyLayer and add a rule for lemmy_comment: 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 Crow. Nothing to install.
lemmy_comment 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 lemmy_comment 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 lemmy_comment. 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.
lemmy_comment is provided by the Crow MCP server (kh0pper/crow). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Crow, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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576 Crow tools catalogued and risk-classified — across an index of 43,000+ MCP servers.