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

With no annotations, the description carries the full burden and does so well: it discloses the cost model (free, no account), a concrete rate limit (25 email verifications per day), the one-time nature of the return ('Returns the key once'), and the exact authentication usage ('Authorization: Bearer <api_key>'). These are non-obvious traits an agent could not infer from structured fields.

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 tight sentences, front-loaded with the core action and cost, followed by the optionality caveat and the critical one-time-return/auth detail. Every sentence earns its place.

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?

With no annotations and no output schema, the description covers the important unknowns: what you get back (a key), that it is returned only once, and how to use it. It stops short of key lifetime, revocation, or what happens on a repeat call, which would complete the picture.

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 all three parameters (name, contact, purpose) are documented in the schema, so the baseline is 3. The description adds no parameter-level detail beyond what the schema already provides.

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 ('Get your own free API key for this server') and immediately clarifies scope: it is for your own quota and the list tools, which distinguishes it from the sibling verification tools that run on a shared trial. An agent can tell what this does without opening the schema.

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 frames the tool as optional ('the verification tools already work without a key on a shared trial'), which is real when/when-not guidance for an agent deciding whether to call it. It does not name a specific alternative sibling tool by name, keeping it 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.