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 useful because it tells the agent values will not be used or persisted, but it does not disclose whether only top-level keys are counted, whether the operation is read-only with no side effects, or what return value the agent should expect.

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-loops the core action; both sentences earn their place. The tradeoff is that the brevity approaches under-specification, though for this dimension the text itself contains no waste.

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, no annotations, and no output schema, the agent has only this one-line description to infer how to invoke it. It fails to explain the mapping between the parameter object and the JSON object being counted, what counts as a key, and what the tool returns, leaving meaningful ambiguity.

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 because each parameter already has an individual description. The tool description only adds a generic 'values discarded' notion, which is already reflected across the parameter descriptions, and it does not explain how the 9 parameters relate to the counted JSON object.

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 clear verb and resource: count keys in a JSON object, values ignored. However, it never identifies which object is being counted: the tool takes 9 optional string parameters and has no explicit JSON-object property, so the agent must guess whether to count keys in the input arguments or in JSON text inside the 'json' parameter.

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 usage guidance is given: no scenarios, no preconditions, no exclusions, and no comparison to sibling tools such as validate-json or the other shape/count tools. The only clue is the tautology that this counts keys, which does not help the agent decide when to choose it over alternatives.

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