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

Annotations only cover readOnly/openWorld, so the description carries the interesting behavior and does so well: it discloses the two-step x402 flow (the call returns the exact HTTP request and payment requirements rather than the data itself) and the cost and client needed to complete payment. That is critical context an agent cannot infer from the schema.

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?

Three dense sentences, front-loaded with the payment requirement and resource scope, with no filler. Slightly telegraphic (filter list is run-together), but 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?

There is no output schema, and the description correctly explains what the call returns (HTTP request + x402 payment requirements) and how to finish the flow. Minor gaps remain around pagination, error handling, or what happens post-payment, but the essential picture is complete.

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?

With only 43% schema coverage, the description compensates by listing all seven filters with their salient values (auth=none, alive=yes, https=yes, limit<=50). It adds real meaning beyond the schema, though 'category' and 'kind' values are left without explanation.

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 (Search) and a precisely quantified resource (2,230 link-checked public & free-tier APIs across 59 categories). An agent can immediately distinguish it from siblings like free_tiers, list_endpoints, or x402_services.

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 flags that this is a paid call ($0.01 USDC via x402), which is a real usage consideration, but it never states when to prefer this over alternatives such as free_tiers or x402_services, nor any when-not condition. Usage is implied through cost rather than guidance.

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