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

Beyond the readOnlyHint and openWorldHint annotations, the description adds meaningful behavioral details: results are ranked by live price, uptime, and speed, include example inputs, and there is a free tier followed by a per-call fee via x402. This gives the agent practical expectations about cost and output ordering.

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 two sentences with no filler. It front-loads the core instruction ('Describe what you need'), states the result and ranking criteria, and then gives essential pricing information. Every clause earns its place.

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?

The description is complete enough for a search/discovery tool: it explains the input, output ranking, and cost model. It does not describe a return format, but it names the key output dimensions and there is no output schema to satisfy, so this is a minor gap.

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 description coverage is 100%, so the schema already documents all three parameters. The description adds context about paid APIs and pricing that helps interpret max_price_usd, but it does not add new semantic detail beyond what the schema provides, so the baseline score of 3 applies.

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 uses a specific verb and resource: 'find the cheapest WORKING paid APIs' for a described task. It clearly conveys the tool's discovery function and distinguishes it from the sibling tools like check_x402_service, which likely verify a specific service rather than search for one.

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 clearly implies when to use this tool: when you need to find the cheapest working paid API for a task, with the user describing their need in plain words. It does not explicitly state exclusions or alternatives, but the context and phrasing make the intended use clear.

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