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

Discloses that the call is free, creates an account, and returns credentials. Annotations already indicate non-readOnly and non-idempotent. Could add detail on email verification or rate limits, but provides solid context.

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 pack all essential information: free one-step registration, use case, and post-call instructions. No redundant words, front-loaded with key action.

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 output schema and 100% schema coverage, the description covers purpose, usage, and parameter guidance thoroughly. No missing information for a self-registration tool.

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?

Adds significant meaning beyond the schema: specifies that email must be durable (disposable domains rejected) and that password is optional and auto-generated if omitted. This helps the agent select valid inputs.

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 clearly states the tool creates a new SibFly account with an API key and free starter credits in one call. The verb 'create' and resource 'account' are explicit, and the context of no human/captcha/card differentiates it from any potential alternative registration flows.

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?

Explicitly says 'Use this when you have no API key' and instructs to save and reuse the api_key. However, it does not explicitly mention when not to use, such as if the user already has an account.

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