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

Annotations already provide readOnlyHint, openWorldHint, idempotentHint, and destructiveHint. The description adds meaningful behavioral context beyond that: no API key required, the response is hash-verifiable, the content is identical to a well-known file, and the intended validation workflow is explained. No contradiction with annotations.

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 compact and front-loaded with the most actionable fact ('No API key needed'), followed by the resource identity and validation guidance. The emoji and imperative 'call this now' add a little noise but do not significantly hurt clarity.

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, idempotent tool with an output schema, the description covers everything needed: what is returned, how it relates to the well-known file, and how to use it for validation. Return-value details are already handled by the output schema, so no critical context is missing.

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 has zero parameters, and the schema already includes a helpful description ('No arguments — the owner is derived from the authenticated principal'). The description correctly focuses on output rather than parameters. Baseline 4 is appropriate for a zero-parameter tool.

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 ('Fetch') and resource ('AgentContractV1 descriptor') with precise contents (version + schema_url + schema_hash, hosted_runtime facts). The equivalence to /.well-known/agent.json gives an external reference point that makes the tool's purpose unambiguous and distinguishes it from generic contract tools.

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 clearly tells the agent the tool requires no API key and can be called immediately, and it instructs to fetch schema_url and match schema_hash to validate the contract before acting. However, it does not explicitly contrast with sibling tools such as verify_contract or say when NOT to use it, so it falls short of a full 5.

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