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

With no annotations, the description must disclose behavioral details. It only says 'Values discarded,' which is minimal. It does not state whether keys are counted recursively, what happens with invalid JSON, 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 two short sentences with no filler. The core action is front-loaded in 'Count keys in a JSON object,' and the second sentence adds a clarifying detail. This is appropriately concise.

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 nine parameters, no annotations, and no output schema, yet the description does not explain which parameter carries the JSON object, what counts as a 'key,' or how the result is returned. This is insufficient 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 coverage is 100%, so each parameter already has a description. The tool-level description does not elaborate on parameter syntax or selection, but it does add meaning by indicating that the JSON input is used for counting keys rather than validation, which is the schema's stated purpose.

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 and resource: 'Count keys in a JSON object.' This is clear and distinguishes the tool from vague alternatives. However, it does not mention sibling tools or explicitly connect the action to the `json` parameter, so it falls short of 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?

No usage guidance is provided. The description does not say when to prefer this tool over sibling tools such as validate-json or other shape-check utilities, nor does it indicate which of the nine schema parameters should be supplied.

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