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

With no annotations provided, the description carries the behavioral burden. It does disclose a non-obvious behavior — 'Values discarded' — indicating that only the key count matters and values are not returned. But it omits other behavioral context such as whether the operation is read-only, how errors are handled, or what side effects, if any, occur.

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 main action is front-loaded and the behavioral note 'Values discarded' 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?

For a tool with nine optional parameters and no output schema, this description is too sparse. It does not specify how to provide the JSON object, whether the count is top-level or recursive, what the return value looks like, or what happens with an empty/invalid input.

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 schema already documents each parameter. The tool description adds the general rule that values are ignored, but it does not resolve how the nine optional string parameters relate to the 'JSON object' being counted, so it adds little beyond the schema.

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 uses a specific verb and object — 'Count keys in a JSON object' — which clearly signals a counting operation and is distinct from sibling shape/validation tools. However, it doesn't clarify which of the nine input properties actually contains the JSON object, so there is some ambiguity.

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 guidance is given about when to use this tool versus validate-json, domain-shape, or other sibling tools. The intended selection condition is only implied by the action of counting keys; there are no usage conditions, exclusions, or mention of alternatives.

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