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

With no annotations, the description carries the full behavioral burden and does so strongly: 'Free, no side effects — does not evict the cache or touch relays.' This tells an agent exactly what will and will not happen, beyond what the input schema can express.

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?

Every sentence earns its place: purpose is front-loaded, the use-case analogy is one sentence, and the side-effect guarantee is a short closing statement. There is no filler or repetition.

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?

Given the presence of an output schema, two well-described parameters, and a clear no-side-effects guarantee, the description fully equips an agent to select and invoke the tool correctly. It also explains the business motivation, which is not captured by the structured fields.

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 input schema already provides complete descriptions for both parameters at 100% coverage, including where dpop_token comes from and the expected npub format. The tool description adds little parameter-level meaning beyond the word 'previously-cached,' so the baseline of 3 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 opens with a specific verb-resource pair: 'Check whether a previously-cached dpop_token is still valid.' It also connects to the npub-proof flow and names the check_oauth_status analog, making it easy for an agent to distinguish this from the many other status and check tools.

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 gives a clear use case: ask whether the next paid call will accept the dpop_token before burning credits on a guaranteed failure. It names check_oauth_status as the analog, though it does not explicitly say when not to use this tool or list alternatives.

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