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

Annotations only state readOnlyHint=false and destructiveHint=false; the description adds crucial behavioral detail: it's an 'intent only' call, returns credits_pending, does not grant spendable credits until confirm_credits succeeds, requires a caller key, and operates with 'No live Stripe' (test mode). This goes well beyond the annotations and helps an agent set expectations.

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 concise sentences that front-load the core purpose and endpoint, then immediately convey key behavioral caveats (intent-only, pending status, confirmation requirement, auth, test mode). Every sentence contributes unique information; there is no filler or repetition.

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 (credits_pending), the side-effect (credits not granted), the auth requirement, and the test environment. This is nearly complete; it could optionally mention error cases or how the returned pending credit relates to confirm_credits, but those are minor for an agent to infer.

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% and the only parameter, pack_id, is already documented with a clear source ('from list_credit_packs') and example. The description adds no extra meaning to the parameter, so the baseline 3 is appropriate.

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 specific verb ('checkout' intent) and resource ('pack'), names the endpoint (POST /credits/checkout), and explicitly distinguishes this from confirm_credits by noting credits are not granted until that sibling succeeds. This leaves no ambiguity about what the tool does.

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 clarifies the intended flow: checkout first, then confirm_credits, and notes the prerequisite of a caller key. It does not name other siblings (e.g., quote_credits, list_credit_packs) as alternatives, but the step-by-step context is clear enough for an agent to know when to invoke it.

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