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

With no annotations, the description carries the behavioral burden, and 'Values discarded' is a useful signal that this is a read-only style operation returning only a count. However, it does not mention output format, edge cases, or whether the count is top-level only, leaving some behavioral ambiguity.

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 a single sentence with no wasted words. The core verb and resource are front-loaded, and 'Values discarded' is placed right after the main behavior.

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 simple counting tool, the one-liner is nearly adequate, but the definition does not explicitly map the operation to the `json` parameter or describe the return value. With many sibling tools and no output schema, the invocation contract is minimally specified rather than fully 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 coverage is 100%, so the description is not required to repeat param docs and the baseline is 3. The description adds no specific parameter guidance, such as clarifying that the `json` string is the value 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 operation ('Count keys') and resource ('a JSON object'), and 'Values discarded' adds useful scope. It does not, however, contrast with sibling tools such as validate-json or domain-shape, so it earns a 4 rather than a 5.

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?

Usage is only implied by the verb: an agent would infer it should use this tool when it needs to count keys in a JSON object. There is no explicit mention of when not to use it or which sibling alternative to choose instead.

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