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

No annotations, so the description carries the full burden. It discloses the input/output contract (values in, frequency map out), which is genuinely useful, but says nothing about ordering of keys, handling of empty input, or the value format (the param is typed string, not array, which is left unexplained).

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, purpose first and return contract second, with zero filler. Front-loaded and fully earned.

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 trivial single-param tool this is close to sufficient: purpose, input, and output are all stated. But with no annotations and no output schema, the odd string-typed 'values' parameter and the shape of the frequency map remain underspecified.

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%, so the schema already documents 'values'. The description restates the same information ('Provide values') without adding syntax or format detail, so baseline 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?

States a specific verb (count) and resource (distinct values in an array) and even names the output form (frequency map). It is unmistakably distinct from near siblings like x402-frequency or x402-group-by.

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 implies usage ('Provide values; returns a frequency map') so an agent understands the context, but it never states when-not to use it or names alternatives like x402-frequency or x402-unique-count. Usage is only implicit.

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