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

Annotations already cover the safety profile (readOnly, idempotent, non-destructure), so the bar for added value is higher. The description adds real extras: no API key required, output equivalence to /.well-known/agent.json, and hash-verifiability semantics. No contradiction with any annotation flag.

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?

Three sentences, and the most actionable fact (no API key needed) is front-loaded. Minor waste: the emoji and 'call this now' are promotional, and the third sentence repeats 'Fetch' while partially restating the first. Still compact and largely earned.

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 tool that already has a full output schema and rich safety annotations, the description covers purpose, authentication prerequisites, output equivalence, and the intended before-acting usage. Nothing essential for correct invocation 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?

With zero parameters, the schema already fully documents input, so the baseline is 4. The description adds useful clarification that version/schema_url/schema_hash are returned facts rather than arguments an agent should supply, preventing a common misuse.

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') with a specific resource: the 'AgentContractV1 descriptor (version + schema_url + schema_hash)' plus 'hosted_runtime facts'. It also anchors the output to a known standard ('identical to /.well-known/agent.json'), making unambiguous exactly what the tool returns.

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?

'No API key needed — call this now' is explicit call-time guidance, and 'validate the platform contract before acting' indicates when in a workflow the tool belongs. However, it does not name sibling alternatives (e.g., verify_contract) or state when not to use it, so it stops short of full exclusion guidance.

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