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

With no annotations present, the description carries the burden of explaining behavior. It does disclose one useful trait: values are discarded and only key names matter. However, it leaves important behavior unclear, such as whether nested keys are counted, what happens with invalid JSON, and what exact result is returned.

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 and front-loaded: the primary action appears in the first sentence, and the second short sentence adds behavioral clarity without redundancy. Every word earns its place.

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 the simple operation, the context is not fully covered. There is no output schema and no explicit statement that a count is returned, no clarification of top-level versus recursive counting, and no guidance about which of the many optional-looking parameters should actually be supplied. The agent is left to infer too much.

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-level detail. The `json` parameter is inferable as the JSON text to count keys from, but the tool description never explicitly maps 'JSON object' to a specific parameter, and the schema's `json` description says 'validate' rather than 'count keys.'

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: count keys in a JSON object. It also adds a meaningful behavioral clarification that values are discarded. It does not explicitly differentiate itself from sibling tools like validate-json, but the core purpose is clear.

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 about when to use this tool versus alternatives such as validate-json or other JSON-related tools. There is no mention of when counting keys is appropriate, what inputs are required, or how to interpret the result in context.

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