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

With annotations providing no meaningful safety hints (readOnlyHint=false, destructiveHint=false, openWorldHint=false), the description carries the full burden and does so well: it discloses email sending, account creation on confirmation, pollToken return, no key shown in browser, rate limits, and link expiry. There is no contradiction with 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 compact and front-loaded with the core purpose, followed by essential flow details, rate limits, and expiry. Every sentence adds meaningful information with 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?

Despite having no output schema, the description explains the return value (pollToken), the follow-up tool, the email/account side effects, and operational constraints. An agent has enough context to invoke the tool correctly and know what happens next.

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?

Schema description coverage is 100%, and the schema already explains email and clientName in sufficient detail. The tool description adds a rate-limit note tied to email but does not substantially enrich parameter meaning beyond the schema, so baseline 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 and resource ('Get a Usero API key') and explains the email-confirmation flow that distinguishes this tool from the sibling check_signup. It clearly states that this tool starts the signup process and returns a pollToken, while check_signup collects the key.

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 positions start_signup as the initiating step and explicitly references check_signup as the follow-up, so an agent can infer the intended sequence. It does not list explicit 'when not to use' conditions, but the flow is clear enough for correct selection.

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