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

With no annotations, the description carries the burden of behavioral disclosure. 'Values discarded' is a useful and explicit disclosure that input values are ignored, which implies a read-only, side-effect-free operation. Still, it does not state the return format, whether nested keys are counted, or behavior on empty/invalid input.

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 short sentences with no filler. The core purpose is front-loaded and the behavioral note earns its place, making this an appropriately concise definition.

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?

Despite full schema coverage, the tool has 9 optional parameters, no annotations, no output schema, and many siblings. The one-line description does not explain how to invoke the tool, what the return value is, or when to prefer it, leaving significant context missing for an agent.

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 baseline is 3. The description adds the cross-parameter insight that values are discarded, but it does not clarify which parameter represents the JSON object to count or how the nine optional parameters relate to the stated purpose.

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 states a specific verb ('Count') and resource ('keys in a JSON object'), and adds a clarifying behavioral note ('Values discarded'). It is not a tautology and is distinguishable from siblings like validate-json. However, it does not explicitly connect the 'JSON object' to the tool's input arguments or to a specific parameter, leaving a minor ambiguity.

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 guidance about when to use this tool versus alternatives. It does not mention sibling tools like validate-json or any conditions for selection, so the agent must infer usage entirely from the name and one-line description.

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