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

With no annotations, the description must carry the behavioral burden. It does disclose one key behavior: values are ignored and only keys are counted. It does not clarify whether nested keys are counted or whether the result is a simple integer, and it says nothing about side effects, though counting is inherently read-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 extremely short and front-loaded: the action and resource are in the first words. It earns its place, though the brevity borders on under-specification.

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?

Given 9 optional parameters, no output schema, and no invocation example, the description is insufficiently complete. An agent cannot tell how to structure the call, what value will be returned, or whether nested keys are included, so this needs more behavioral context.

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?

The input schema already documents all 9 parameters in full (100% coverage), so the baseline is 3. The description adds only the general rule that values are discarded, which applies to every parameter but does not clarify how the 'json' parameter or any other single parameter supplies the object to count.

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 specific action (count keys) and a clear resource (a JSON object), and distinguishes itself from validation or shape-check siblings by emphasizing that values are discarded. However, it does not explicitly map the JSON object to the input schema's parameters, leaving some ambiguity about what to pass.

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 on when to choose this tool over siblings like validate-json or domain-shape. 'Values discarded' implies a use case where only key presence matters, but no alternative or exclusion is stated.

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