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

With readOnlyHint and idempotentHint already in annotations, the description adds useful context: no API key is required, the response is identical to /.well-known/agent.json, and schema_hash matching is the validation mechanism. There is 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 short and front-loaded with the most actionable fact ('No API key needed'). The emoji and 'call this now' are mildly promotional, but they do not add meaningful length or obscure the content.

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 read-only, parameterless tool with an output schema and annotations, the description covers purpose, authentication, exact wire equivalence, and the validation workflow. Nothing material is missing for an agent to decide whether and how to call it.

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 schema already covers the parameter space fully. The baseline for a 0-parameter tool is 4; the description adds no special parameter behavior, but none is needed.

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?

Description clearly identifies the action (fetch) and resource (AgentContractV1 descriptor with version, schema_url, schema_hash) plus hosted_runtime facts, and points to /.well-known/agent.json. It doesn't explicitly distinguish itself from the sibling verify_contract, so it stops 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?

It states an enabling condition ('No API key needed — call this now') and a timing ('before acting'), which implies when to call. However it gives no explicit exclusion or pointer to the closely related verify_contract alternative, leaving the selection decision to inference.

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