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

Annotations already cover readOnly and idempotent behavior. The description adds that no API key is required and that it is used to validate the platform contract, which gives useful behavioral context without contradicting the 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 important facts. The 'call this now' phrasing is slightly promotional, and 'Fetch schema_url and match schema_hash' repeats part of the prior sentence, but the overall structure is efficient.

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?

It explains what the tool returns (descriptor fields and hosted_runtime facts) and why it should be used (validate before acting). It does not mention error cases, but for a simple read-only fetch this is adequate.

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?

There are zero parameters, so there is nothing to explain. The baseline for a no-parameter tool is 4, and the description adds no irrelevant parameter detail.

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 identifies the tool as fetching the AgentContractV1 descriptor and hosted_runtime facts, and even equates it to /.well-known/agent.json. This is specific and distinguishable from the sibling tools like verify_contract.

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 that no API key is needed and instructs to call it now, implying it is an initial discovery/validation step before acting. It does not explicitly contrast with alternatives, but the context is clear enough.

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