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

The description goes well beyond the annotations by revealing that signup requires no password, returns an API key and verify link, and is conditional on verification: an unopened verify_url expires after one hour. It also discloses the free-tier quota expansion once verified. This gives the agent a realistic model of the tool's side effects.

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 four sentences each carry distinct information: account creation and returned values, immediate usability, verification and quota expansion, and expiration. The main result is front-loaded in the first sentence. 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?

For a one-parameter tool with no output schema, the description covers the key return values (API key, verify_url) and the lifecycle behavior that would otherwise be unpredictable. It could mention handling of already-registered emails, but the essential success path is complete and actionable.

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 fully documents the single `email` parameter, so the baseline is 3. The description adds only that the email is used to create the account and receive the verify link, without adding format or validation details. This is adequate but does not meaningfully extend the schema.

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 states a specific verb and resource: it creates an avacast account with an email and returns an API key plus verify_url. It clearly distinguishes signup from siblings like create_api_key or create_session, which do not create the account. The no-password detail adds further precision.

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 clearly frames the signup scenario and explains that the returned key can be used immediately, which implies this is the entry point before other session/key tools. However, it does not explicitly name alternatives or state when not to use it, such as when resending verification or creating additional API keys. This is clear context without exclusions.

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