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

With no annotations, the description must carry behavioral disclosure; it states that values are discarded, but does not mention output format, invalid JSON handling, or whether nested keys are counted. 'Discarded' is also potentially misleading about side effects.

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 extremely concise: two short sentences with no filler or redundant 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?

For a tool with 9 optional parameters and no output schema or annotations, the description lacks essential context such as which parameter to populate, the return format, and edge-case behavior. It states the core purpose but is not complete enough for reliable invocation.

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?

Although every parameter has a schema description, the tool description does not indicate which parameter holds the JSON object, and the 'json' parameter's schema description says 'JSON text to validate; discarded after the check', which contradicts the counting purpose. The other parameters are unrelated and all are optional, leaving the agent without actionable parameter guidance.

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 clearly states the tool counts keys in a JSON object and ignores values, which is a specific verb and resource. However, it does not explicitly tie this to the 'json' input parameter, so there is slight 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?

The description gives no guidance on when to use this tool instead of related siblings like validate-json or search-query-len. The purpose implies a key-counting use case, but no explicit when/when-not conditions are provided.

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