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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and non-destructive behavior. The description adds genuinely useful context beyond those hints: no API key is required, the payload is hash-verifiable, and it matches the well-known agent contract endpoint. This enriches the agent's understanding of the tool's trust and safety profile.

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 short, front-loaded with the most important fact ('No API key needed'), and includes a concrete validation workflow. The emoji and imperative 'call this now' are slightly informal but not wasteful. The only minor redundancy is that fetching schema_url and matching schema_hash restates fields already listed, but it does so to explain the tool's purpose.

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 zero-parameter, read-only tool with rich annotations and an output schema, the description covers everything an agent needs: authentication burden, what the return payload represents, and how to use the returned data for contract validation. There is no missing behavioral or usage context that would prevent correct invocation.

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?

The tool takes zero parameters, so the baseline is 4. The schema's own description adds that the owner is derived from the authenticated principal, and the tool description adds no conflicting or confusing parameter information. Nothing is missing.

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 clearly states a specific verb ('Fetch'), a specific resource ('AgentContractV1 descriptor'), and the exact contents (version + schema_url + schema_hash, hosted_runtime facts). It even equates the output to /.well-known/agent.json, making the purpose unambiguous. However, it does not explicitly distinguish itself from sibling tools like verify_contract, so it falls short of a 5.

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?

The description gives an implied usage directive: 'call this now' and 'before acting' suggest this should be an early validation step. It also explains why it is safe to call ('No API key needed'). But it does not explicitly state when not to use this tool or compare it with alternatives among the siblings, so the guidance is mostly implicit.

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