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

With no annotations, the description carries the behavioral burden. 'Values discarded' is a useful explicit behavioral detail, but the description does not clarify whether counting is top-level or recursive, whether the input is mutated, or what exactly 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 concise and front-loaded, with no filler. The second sentence adds meaningful behavioral information, though the overall terseness leaves some operational details unstated.

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?

The definition is minimally sufficient for a simple count operation, but it has gaps: no output schema, no statement about recursion versus top-level keys, and many optional parameters without a clear mapping to the JSON object being counted.

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 notion of a JSON object with keys, but it does not map the operation to a specific parameter such as json, and many listed parameters are marked discarded, leaving some ambiguity for the agent.

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 clear, specific action: count keys in a JSON object, with values ignored. It is more informative than the tool name alone, but it does not explicitly differentiate itself from sibling tools such as validate-json.

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 use case is implied: call this tool when you need to count keys in a JSON object. However, there is no explicit guidance about when not to use it, no prerequisites, and no mention of alternatives like validate-json.

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