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

Annotations cover readOnly/openWorld, but the description adds substantial context beyond them: data provenance (nerdwallet.com public 'best credit cards' pages via residential proxy), that rankings are editorial picks not neutral data, and a clear pricing model ($0.002 USDC per successful call via x402, failed calls free). This is exactly the behavioral context annotations cannot carry.

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 returned fields, then adds provenance and pricing. Dense but nearly every clause carries information. The parenthetical category list slightly duplicates the schema, keeping it from a 5.

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-shape explanation is unnecessary. The description covers data source, editorial nature, and the payment mechanism, leaving nothing an agent needs to invoke it correctly.

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 schema already documents the slug format and example values. The description echoes the same category list, adding little beyond the schema; 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+resource ('best credit card rankings for a category') and enumerates exactly what is returned (rank, card name, 'best for', annual fee, star rating, image, link). An agent can immediately tell this is a NerdWallet credit-card ranking fetch, distinct from the crypto/finance price-feed siblings.

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?

Usage is implied by 'rankings for a category' and the example slugs, but there is no explicit when-to-use/when-not guidance or mention of an alternative. Since no sibling tool overlaps this capability, the lack of routing is understandable, but it still leaves the agent to infer fit.

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