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

With no annotations, the description bears the full burden of behavioral disclosure. It mentions that values are discarded, which is a side effect, but it does not indicate whether the operation is read-only, what it returns, or any other side effects. This is insufficient for a tool with no annotation support.

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 that is both concise and front-loaded with the primary action. There is no wasted wording, and it is appropriately sized for the simple operation it describes.

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?

This is a tool with 9 optional parameters, no output schema, and no annotations, yet the description is only one line. It fails to explain how the many unrelated parameters (url, city, feed, host, etc.) relate to counting keys, leaving the agent to guess the correct usage. This is completely inadequate for the tool's complexity.

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 baseline is 3. The description adds no meaning beyond the schema; it does not clarify which parameter contains the JSON object, despite the 'json' parameter being described as 'JSON text to validate; discarded after the check'. The description neither enhances nor contradicts 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 states a clear action: count keys in a JSON object, with values discarded. This is a specific verb-resource pair that distinguishes it from validation or shaping tools. However, it doesn't explicitly tie the action to any of the 9 schema parameters, leaving ambiguity about the actual input.

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 like validate-json or domain-shape. The description only states what it does, not when to choose it, and there is no mention of exclusions or alternative tools.

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