Request a trial API key

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

Annotations only say it is a non-read-only, open-world, non-idempotent call; the description goes well beyond that by disclosing the 3-keys-per-IP-per-day rate cap, that the key is adopted by the server for the rest of the session, and that it is returned exactly once and must be persisted by the user in MCP config. That is exactly the operational context an agent cannot 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?

Front-loaded with the core action and limits, then the trigger condition, then the session/return behavior, then the durable alternative. Every sentence carries distinct information with no restatement of the title.

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?

An output schema exists so return values need not be explained, and the description still covers limits, session adoption, persistence instructions, and escalation paths. Nothing an agent needs to call this correctly or explain the result to a user is missing.

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% for both optional parameters (agent, purpose), so the schema already carries their meaning. The description adds no extra syntax, format, or example guidance for either field, so the baseline 3 applies.

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+resource (self-issue an AllRatesToday API key) plus the exact scope: 100 lifetime calls, 7-day validity, no account or email. This is unmistakably distinct from the read-only rate siblings, which none of them create credentials.

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?

Gives an explicit trigger ('when another tool answered "needs an API key" and the user wants real-time rates or history right now') and names the alternative for the opposite case ('For a lasting key, register at ... or see pricing'). Both the when and the when-not are covered.

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