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

Annotations already declare readOnly, idempotent, openWorld, and non-destructive behavior. The description adds a concrete behavioral note (no API key needed) and explains the validation workflow (match schema_hash), which gives the agent a clear picture of side effects and expected outcomes. It does not mention error cases, but the core behavior is well disclosed.

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 verbose and includes redundant content. The phrase '✅ No API key needed — call this now' adds little value, and the third sentence repeats the action of fetching schema_url and schema_hash already covered in the second sentence. This reduces clarity and could be trimmed to a single concise sentence.

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?

Given the tool is a simple getter with no parameters and an output schema exists, the description covers the main elements: what is returned (descriptor and hosted_runtime facts) and how to use it for validation. It does not discuss edge cases or comparisons to siblings, but for this purpose, the information is reasonably complete.

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 input schema already explains 'No arguments — the owner is derived from the authenticated principal.' The description does not add any parameter-related information beyond that, matching the baseline for high schema coverage. No additional meaning is needed for parameters.

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 the tool fetches the AgentContractV1 descriptor and hosted_runtime facts, explicitly listing the components (version, schema_url, schema_hash) and noting it is identical to /.well-known/agent.json. It uses a specific verb ('Fetch') and the resource is well-defined, making the purpose unambiguous.

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 provides guidance on when to use the tool: it states no API key is needed, suggests calling it 'now,' and instructs to validate the platform contract before acting. While it does not explicitly contrast with sibling tools like verify_contract, the recommendation to use it as a preliminary validation step gives adequate usage context.

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