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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false. The description adds valuable behavioral context: the data is hash-verifiable, matches a known endpoint, and that schema_url/schema_hash should be compared. This goes beyond the annotations without contradicting them.

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 two sentences and front-loads the actionable instruction. The emoji and 'call this now' add a slight informal tone but do not reduce clarity. Every clause contributes meaning; no filler.

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 present, the description covers what it returns, why it exists, and how to use it. It does not enumerate the exact fields of the host_runtime facts, but the output schema handles that. The validation step is explicitly mentioned, making the tool's role 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?

There are zero parameters, so the description has no parameter burden. The schema has full coverage (100%) and the note about deriving the owner from the authenticated principal is in the schema description. The tool description correctly focuses purely on behavior.

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'), a clear resource ('AgentContractV1 descriptor'), and the key components (version + schema_url + schema_hash). It also explicitly links the tool to /.well-known/agent.json, making its purpose unmistakable even among siblings.

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 gives an explicit 'call this now' directive and explains that no API key is needed, which is actionable usage guidance. It also mentions validating the contract 'before acting', implying a temporal context. However, it does not explicitly contrast with siblings like verify_contract, so a small inference gap remains.

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