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

The description discloses that values are discarded, which is a meaningful behavioral trait beyond the tool name. However, with no annotations available, it does not state whether keys are counted at the top level only, how invalid JSON is handled, or what the return value looks like.

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 short and front-loaded, with the primary operation stated first and the discarded-values behavior stated second. No filler or redundant wording is present, though the terseness leaves some behavioral gaps covered elsewhere.

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 9 optional parameters, no output schema, and no annotations, yet the description does not identify which parameter carries the JSON object, the counting depth, the return format, or error behavior. An agent could infer the 'json' parameter from the schema, but the description alone is not enough for reliable invocation.

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 and the description does not need to re-document parameters. The description itself adds no parameter-level meaning, and the schema's 'json' parameter mentions validation rather than key counting, but the overall parameter documentation is sufficient for a baseline score.

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 identifies the operation ('count keys') and the resource ('a JSON object'), and 'values discarded' clarifies what is ignored. It does not explicitly distinguish itself from sibling tools like validate-json, but the core purpose is unambiguous.

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 such as validate-json or other count/shape tools. 'Values discarded' only weakly implies a use case where values are irrelevant; no explicit when-to-use or when-not-to-use guidance is provided.

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