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

The readOnlyHint, idempotentHint, and destructiveHint=false annotations already establish the safety profile. The description adds meaningful behavior beyond annotations: it clarifies that no API key is required, that the result is hash-verifiable, and that it is identical to /.well-known/agent.json. The only small omission is not explicitly describing the return envelope, but the rich annotations plus the explicit equivalence offset that.

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 two sentences and wastes little space, leading with the most actionable fact ('No API key needed — call this now'). The second sentence bundles the descriptor contents and the hash-validation instruction. It could be slightly tighter by trimming the repetition of schema_url, but it is well front-loaded and compact.

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?

The tool has no parameters, a rich annotation set, and an output schema, so the description's main job is to explain the contract resource and the validation step, which it does. It explains the purpose, the runtime facts, the file equivalence, and the validation workflow. An agent can invoke it correctly without further lookup; only a minor detail about the exact shape of the output remains, but the output schema covers that.

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 input schema has zero parameters and 100% schema description coverage, so the schema already explains everything about arguments. The description adds a useful behavioral note ('owner derived from authenticated principal') that compensates for the empty schema. With no parameters to document, this is effectively a strong pass.

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 enumerates the exact contents (version, schema_url, schema_hash, hosted_runtime facts). It distinguishes itself by equating the response to /.well-known/agent.json, so an agent knows exactly what it is getting and can separate it from sibling 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?

The description explicitly says 'No API key needed — call this now' and instructs to fetch schema_url and match schema_hash before acting. This gives both an immediate when-to-use signal and a concrete validation workflow, which is strong usage guidance for a contract-checking tool.

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