Block a remote domain at the user level (hide all accounts from that domain for the authenticated user). For instance-wide defederation use mastodon_defederate. Rate-limited: 5/hour.
AI agents use mastodon_block_domain 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 modifies the authenticated user's account settings by adding a domain block, which is a reversible write action. It is not destructive since the block can be undone, and it doesn't delete data or move money. The blast radius is medium — misuse could block legitimate domains for the user, disrupting communication, but it is scoped to the user level and reversible.
From the tool's definition Block a remote domain at the user level (hide all accounts from that domain for the authenticated user)
Documented attack patterns abuse exactly the kind of access mastodon_block_domain 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 mastodon_block_domain:
{
"version": "1",
"default": "deny",
"tools": {
"mastodon_block_domain": {
"limits": [
{
"counter": "mastodon_block_domain_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}mastodon_block_domain 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.
Block a remote domain at the user level (hide all accounts from that domain for the authenticated user). For instance-wide defederation use mastodon_defederate. Rate-limited: 5/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 mastodon_block_domain: 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.
mastodon_block_domain 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 mastodon_block_domain 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 mastodon_block_domain. 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.
mastodon_block_domain 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.
Free to start. No card required.
576 Crow tools catalogued and risk-classified — across an index of 43,000+ MCP servers.