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

With no annotations provided, the description carries the full burden. It only discloses that values are discarded, but omits the return format, error behavior, which parameter holds the JSON, and whether it is read-only. The schema's 'json' parameter description ('JSON text to validate') conflicts with the tool's stated purpose of counting keys, adding confusion.

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 concise sentences, front-loading the primary action and a key behavioral note. It is efficient, though it could benefit from a structured mention of the input parameter.

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 and no output schema, the description is insufficient. It does not explain the return value, which parameter to pass, or any constraints. An agent cannot confidently call this tool based on the provided information.

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 each parameter is documented. However, the tool description adds no value beyond the schema; it does not clarify which parameter is the JSON input. The 'json' parameter's description about validation rather than counting leaves the mapping unclear.

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 states a specific action (count keys) and resource (a JSON object), and notes values are discarded. However, it does not specify which parameter carries the JSON input, and the 'json' parameter in the schema is described as 'validate' rather than 'count', creating ambiguity. It also does not distinguish itself from sibling tools like validate-json.

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 on when to use this tool versus alternatives, no prerequisites, and no exclusions. The agent is left to infer usage from the name and minimal description.

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