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

Annotations already declare read-only, idempotent, and non-destructive behavior. The description adds valuable context: no API key requirement, equivalence to the standard well-known endpoint, and the hash-verification workflow. It does not contradict annotations and goes beyond them in disclosing auth and validation specifics.

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?

Two sentences, front-loaded with the most actionable information ('No API key needed — call this now'). It efficiently covers what is fetched, how it is verified, and when to use it, with no wasted words.

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 tool with an output schema, the description fully explains the return fields (version, schema_url, schema_hash, hosted_runtime facts), the validation purpose, and the standard endpoint reference. Nothing essential is missing for correct invocation.

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, so the baseline is 4. The description does not need to explain parameter semantics; the input schema already states that the owner is derived from the authenticated principal, and the description adds no parameter-related details, which is appropriate here.

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 verb 'Fetch' and the resource: a hash-verifiable AgentContractV1 descriptor with version, schema_url, schema_hash, and hosted_runtime facts. It also distinguishes itself from siblings by noting it is identical to the standard /.well-known/agent.json endpoint, making its role 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?

It provides strong contextual guidance: 'No API key needed — call this now' and 'validate the platform contract before acting' clearly indicate this is a safe, preliminary step. However, it does not explicitly name alternatives or state when not to use it, so it lacks the full exclusionary clarity of a 5.

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