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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds relevant behavioral context beyond the annotations: the tool requires no API key and returns content identical to /.well-known/agent.json. It stops short of describing edge cases (e.g., behavior when no contract exists), but what it adds is meaningful.

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, each earning its place: the no-auth call-to-action, the precise payload definition with an equivalence anchor, and the validation workflow. The critical 'call this now' is front-loaded, and there is zero redundant restatement of what the schema or annotations already convey.

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 a rich output schema and clear annotations, the description is nearly complete: it defines what is returned, where the data comes from, and how to use it. The only gap is not describing the exact shape of hosted_runtime facts or what happens if validation fails, but the output schema covers return values and the tool is simple enough that this is not a critical omission.

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 and schema description coverage is 100%, so there are no parameter semantics to compensate for. The description adds clarity about how the owner is resolved ('identical to /.well-known/agent.json' and the schema's 'authenticated principal' context), which is helpful. Since there are no params, the baseline is high and the description fully meets it.

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') and a precise semantic: it retrieves the AgentContractV1 descriptor (version + schema_url + schema_hash) along with hosted_runtime facts. It also explicitly equates the output to /.well-known/agent.json, which unambiguously distinguishes it from any sibling tool that might manipulate or validate contracts.

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 opening line 'No API key needed — call this now' gives an explicit, actionable trigger condition and removes a common prerequisite barrier. The description also tells the agent exactly what to do with the result ('Fetch schema_url and match schema_hash to validate the platform contract before acting'), which is a clear usage directive rather than a mere capability statement.

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