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

Annotations declare readOnlyHint=false with destructiveHint=false, and the description explains why it is a write: it 'deducts prepaid credits from a reusable key,' a non-obvious billing side effect the annotations do not convey. It still omits behavior on insufficient credits, whether failures refund the deduction, and what the result set looks like.

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 compact sentences with the core capability front-loaded and the cost side effect second. Nothing is redundant, though the billing sentence is terse enough to leave the charging model ambiguous.

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?

With no output schema, the description should describe the shape of returned matches and what a credit deduction costs per call; neither is present. For a three-parameter, credit-charging tool this leaves meaningful gaps an agent would want before invoking it.

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 only 33%, and only creditKey carries an inline description; the description's phrase 'reusable key' reinforces that parameter's meaning but adds nothing about its source. The query and limit parameters get no explanation, so the agent must infer that query is free text embedded for similarity and that limit caps result count.

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 names a specific verb and resource: 'Vector similarity search across BuiltWith technologies and categories,' which tells an agent exactly what domain of data is queried. It does not differentiate itself from the sibling vector-api, so an agent cannot tell the two apart from the text alone.

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?

There is no when-to-use guidance: no mention of when vector search is preferable to keyword or category siblings such as x402-keywords-search-api or x402-list-api, and no prerequisites such as needing a purchased credit key first. The only implied condition is the credit key requirement, which is buried in the second sentence.

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