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

With no annotations provided, the description carries the full burden. 'Values discarded' is a useful behavioral disclosure, indicating that only key names matter. However, it does not explain behavior on invalid JSON, nested objects, or which of the nine parameters actually contribute to the count.

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 filler. The core action is front-loaded, and the crucial 'values discarded' detail is included without unnecessary elaboration.

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 tool has nine parameters, none required, no output schema, and no annotations, yet the description only says 'Count keys in a JSON object.' It does not tell the agent which parameter to populate, what the return value looks like, or how the other parameters relate to the operation. A single mention of the json parameter would have made this significantly more complete.

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 even without extra parameter detail in the description. The description does not add meaning beyond the schema, but it also does not need to since each parameter already has a description. The unrelated-looking parameters are not clarified, but that is a completeness gap rather than a parameter-semantics failure.

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 a specific verb and resource: 'Count keys in a JSON object.' This is immediately understandable and distinct from generic tools. However, it does not explicitly differentiate from siblings like validate-json or domain-shape, so it stops short of full sibling differentiation.

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, no prerequisites, and no mention of which input parameter is expected. With 25 sibling tools available, the absence of any usage direction leaves the agent to infer the appropriate context.

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