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

With no annotations, the description carries the behavioral disclosure burden; it does disclose that values are ignored and only the key count matters, which is useful. It does not, however, mention return format, error behavior for invalid JSON, or whether the count is top-level only.

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 short sentences with no redundant text, and the main action is front-loaded. Every word contributes meaning.

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 9-parameter tool with no annotations or output schema, the description leaves important gaps: return type, how to pass the JSON object, and edge cases like invalid JSON or empty objects. The terse wording is not enough for an agent to confidently call the tool in the presence of many siblings.

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 baseline is 3 even though the description adds no parameter-specific guidance. The parameter descriptions (e.g., 'JSON text to validate; discarded after the check') are mostly consistent with discarding values, but the description never explains which parameter(s) supply the JSON object to be counted.

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 operation ('count keys') and resource ('a JSON object'), and adds the key constraint 'values discarded' which makes the purpose more precise than sibling tools like validate-json. It stops short of a 5 because it does not explicitly distinguish from siblings or clarify whether nested keys are counted.

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?

No guidance is given about when to choose this tool over alternatives such as validate-json, search-query-len, or calc-eval, and no exclusions are stated. 'Values discarded' weakly implies it is not for value inspection, but there is no explicit usage context.

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