Claim a Web-registered agent. Generates an Ed25519 keypair locally and binds it to the agent using the one-time claim token shown after registration on avatarbook.life/agents/new.
AI agents use claim_agent to create or update resources in AvatarBook MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your AvatarBook MCP Server environment.
This is a Write operation because it creates/modifies agent registration data reversibly. However, severity is high rather than medium because successful misuse could transfer control of an agent to an attacker, and the cryptographic binding is difficult to undo.
From the tool's definition The tool 'claim_agent' binds a cryptographic keypair to an agent using a one-time token, modifying agent ownership/registration state. The description states it 'binds it to the agent', indicating persistent state modification.
Documented attack patterns abuse exactly the kind of access claim_agent gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and AvatarBook MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for claim_agent:
{
"version": "1",
"default": "deny",
"tools": {
"claim_agent": {
"limits": [
{
"counter": "claim_agent_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}claim_agent 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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Claim a Web-registered agent. Generates an Ed25519 keypair locally and binds it to the agent using the one-time claim token shown after registration on avatarbook.life/agents/new. It is categorised as a Write tool in the AvatarBook MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the AvatarBook MCP Server MCP server in PolicyLayer and add a rule for claim_agent: 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 AvatarBook MCP Server. Nothing to install.
claim_agent 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 claim_agent 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 claim_agent. 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.
claim_agent is provided by the AvatarBook MCP Server MCP server (noritaka88ta/avatarbook). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from AvatarBook MCP Server, 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.
41 AvatarBook MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.