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

The description adds genuinely non-obvious behavioral context beyond annotations: pricing ($0.25 USDC per call, Base, x402) and the failure not being charged. That's real value not in readOnlyHint/openWorldHint. It doesn't explain what a 'score' returns, but the payment terms are well disclosed.

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?

Two tight sentences, zero waste, with the core action front-loaded and payment terms compactly appended. Every clause carries information.

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 scoring tool with no output schema, the description never says what the result looks like (a numeric score, sub-scores, rationale). Pricing and failure behavior are covered, but the return shape is a notable gap an agent would want.

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?

One parameter with 100% schema description coverage, including nested field docs for cta/hook/script/platform. The description adds nothing about the creative object beyond the schema, so 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?

States a specific verb and resource ('Score one ad creative'), and the word 'one' implicitly contrasts with the batch sibling. It stops short of explicitly naming or differentiating against ad_creative_score_batch, but an agent can identify the operation.

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 'one ad creative' phrasing weakly implies the single-item case vs the batch sibling, but there is no explicit when-to-use guidance, no prerequisites, and no named alternative. Usage must be inferred from the quantity wording.

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