Create an MX Probe API key

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

The description discloses real behavioral details beyond the annotations: it creates a key, saves it locally, emails the key, includes a 100-free-check quota, and enforces one key per address. This gives an agent a strong sense of side effects and constraints. No contradiction with annotations.

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 description is three short sentences, front-loaded with the primary return value. Each sentence adds a distinct useful detail: returns a key, saves it locally, and the one-per-address constraint.

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, the description covers the return value, side effects, quota, and a uniqueness constraint. Nothing critical is missing for an agent to correctly invoke it.

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 the baseline is 3. The description adds a bit of context by noting the key is mailed to the given address, but it does not meaningfully extend the schema's explanation of the email parameter.

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 clear verb ('Sign up'), the resource (email address), and the outcome (returns an API key with 100 free checks). It also explains that the key is saved locally, which distinguishes it from the sibling verification and billing tools.

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 implies this is the setup step for the other tools: 'saves it locally for the other tools' tells an agent when this should be used. It does not explicitly say when not to use it or name alternatives, but the context is clear enough.

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