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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely useful context specific to this tool: it is a static, no-side-effect guide that neither initiates payment nor performs network calls. It does not describe the guide's contents or whether the guidance is versioned, which keeps it below a 5.

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?

Two sentences, front-loaded with what it returns and what triggers use, followed by the exclusion clauses. Every clause earns its place by preventing a costly misinterpretation (treating it as a paying endpoint call).

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?

With an output schema present and zero parameters, the description need only establish what the tool is and when to call it, which it does. Minor gap: it does not hint at what the returned guidance contains or that the agent must apply it manually before retrying the paid sibling tools.

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 takes zero parameters, so there is no parameter semantics to explain; baseline is 4. The description correctly signals a no-argument call by saying it returns static guidance with no input described.

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?

States a specific verb ('Returns') and resource ('static guidance for calling the Vybe API with x402 pay-per-call') plus the triggering condition ('no API key is available'). The negative clauses explicitly separate it from the query/build siblings, so an agent can tell it is documentation, not an endpoint call.

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?

Gives a clear condition for use ('when no API key is available') and effectively excludes the action siblings by stating it does not call an endpoint or sign anything. It stops short of naming which sibling to use instead (e.g., query-vybe-api) once credentials exist, but the context is unambiguous.

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