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

With no annotations, the description carries the full burden of behavioral disclosure. It transparently states this is a creation operation ('Create'), discloses the rate limit (1,000 requests/month), and explains how the returned key should be used (as a Bearer token). It does not mention edge cases like duplicate emails or whether the key is returned directly vs emailed, but for such a simple tool the disclosed traits are sufficient.

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, both densely informative, with the purpose front-loaded in the first sentence. No filler or redundant material. The description earns its place with each clause communicating an independent piece of guidance.

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 single-parameter tool with no output schema and no annotations, the description covers the essential context: what the tool does, when to use it, and how to use the result. It omits edge-case behavior (e.g., already-existing key for that email) and exact response format, but these are relatively minor for such a simple operation.

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 0%, so the description must compensate for the undocumented email parameter. The only parameter-related phrase is 'for an email address', which merely restates the parameter name and type without adding meaningful semantics. It does not explain constraints beyond the schema's format field, nor does it clarify what happens if the email is already registered. This is a clear gap.

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 a specific action ('Create'), a specific resource ('free API key'), and the rate limit (1,000 requests/month). It distinguishes this tool from all sibling tools, which are card-related operations, by making clear this is about API key creation rather than card operations.

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 explicitly says 'Use this if you don't have a key yet', providing a clear condition for when to invoke this tool. It also tells the agent what to do with the result ('pass it as Authorization: Bearer <key>'), which effectively guides the next step. This is stronger than merely implying usage.

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