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

Annotations only mark it as a non-read-only, non-destructive, closed-world write. The description goes well beyond that by disclosing the disposable-domain rejection rule, that the account receives free credits, and critically that `api_key.key` is returned ONCE and cannot be retrieved again — a one-time-secret hazard an agent must act on immediately.

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?

Three sentences, front-loaded with what the tool does, then requirements, then the response contract. No filler; the one-time-key warning is stated where an agent will read it before calling.

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?

Even without an output schema, the description enumerates the return payload (account id/email and the api_key) and the ephemerality of the key, which is the only return detail an agent needs to call and handle this tool correctly.

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 coverage is 100%, so both parameters are already documented including the 8-character minimum. The description reinforces the constraints and adds enforcement context (disposable domains rejected) but does not add syntax or format detail beyond the schema, matching the baseline 3.

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 and resource ('Programmatically create a brand-new Verifly account') and frames its role as the agent self-onboarding path, which cleanly separates it from read siblings like get_account, get_credits, and get_started.

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?

Explains the when clearly: no human in the loop, only email and password required, and that the returned key enables subsequent tool calls. It does not name an alternative or an explicit 'do not use this if you already have an account' exclusion, so it falls short of a 5.

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