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

Annotations already mark the tool read-only, idempotent, and non-destructive, so the bar is lower. The description adds meaningful context beyond annotations by stating no API key is required, revealing that the output is identical to /.well-known/agent.json, and explaining that schema_url/schema_hash enable hash verification. This gives the agent a clear behavioral model 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 concise and front-loaded: the most important operational fact ('No API key needed — call this now') comes first, followed by the object being fetched and the validation action. Each sentence adds useful information and there is 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-argument, read-only tool with an output schema, the description is complete: it explains authentication, the exact payload shape, the standard it mirrors, and a concrete post-fetch validation step. No critical calling context appears to be 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?

There are zero parameters and the schema description already states that the owner is derived from the authenticated principal, so parameter semantics are essentially fully covered by the schema. The description adds no parameter-specific detail, but with 0 parameters and 100% schema description coverage, the baseline 4 is appropriate.

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 uses a specific verb ('Fetch') and a precise resource ('hash-verifiable AgentContractV1 descriptor') with the exact fields returned: version, schema_url, schema_hash, and hosted_runtime facts. It also anchors the resource to the well-known standard, /.well-known/agent.json, which makes the tool's purpose unmistakable and implicitly distinguishes it from the sibling verify_contract tool.

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 clear contextual guidance: 'No API key needed — call this now' removes prerequisite uncertainty, and 'before acting' tells the agent when to call the tool. It does not explicitly name alternatives or state when not to use it, so it stops short of a full 5, but the usage context is clear.

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