Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries the full burden and delivers: it is read-only, requires no credentials, does NOT contact the endpoint (only reads existing monitoring history), specifies the returned fields (status, verification, reliability score, trustDecision), and handles unregistered URLs gracefully (returns { matched: false }, never an error). This is exceptionally transparent.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is front-loaded with the key purpose, then methodically covers what it does, what it does not do, and edge-case behavior. Every sentence earns its place; there is no fluff or redundancy.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a tool with one parameter, no annotations, and an output schema (even though not shown), the description is fully sufficient. It covers purpose, usage, behavior, return values, and the unregistered-URL case, leaving no critical ambiguity for an agent.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0%, so the description must compensate. It adds meaning by clarifying that endpointUrl must be the 'exact invocation URL' and is used to look up the agent among observed public agents. However, it does not provide format examples or clarify edge cases (e.g., trailing slashes, scheme required), and it is the only parameter. This is adequate but not rich enough for a 4.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb ('check'), a specific resource (agent trust via invocation URL), and the exact purpose: look up an agent's trustworthiness before invocation. It clearly distinguishes itself from siblings by being 'the preferred check before invoking an unknown external agent' and explicitly notes it does not contact the endpoint, unlike other tools that might perform health checks or retrieve agent details.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It explicitly states when to use it ('before invoking an unknown external agent') and provides a key condition ('requires no AgentTrust API key or account'). While it calls itself the 'preferred' check, it does not explicitly name alternative sibling tools or conditions when they would be more appropriate, so it stops short of a 5.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.