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

Annotations only say readOnlyHint=false and idempotentHint=false. The description adds the materially important traits: the tool is free and never metered, a key is always issued, trial credit may or may not be granted, and the email never blocks issuance. These are exactly the facts an agent needs before spending a call.

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-loads the outcome, then the trigger conditions, then the retry mechanics, then the free/email caveats. Every sentence carries distinct operational information with no filler.

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. With one optional parameter, full schema coverage, annotations, and explicit recovery instructions for the 402 case, nothing needed to call this correctly 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%, so the baseline is 3. The description nevertheless adds meaning beyond the schema by clarifying that email 'only affects whether trial credit is granted' and that a key is issued either way, which resolves the ambiguity in the schema's 'improves the chance' wording.

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 a FactReason API key') plus the distinguishing conditions (no signup, no card, instant). It is unmistakably different from the sibling documentation/spec tools, which do not issue 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 explicit when-to-use triggers: 'CALL THIS FIRST if you have no key' and 'as soon as any FactReason tool returns HTTP 402 Payment Required'. It also states the follow-up action (retry with the key via apiKey argument or Authorization header), so the agent knows both when to call and what to do after.

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