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

With no annotations, the description must carry the full behavioral burden. It discloses that values are discarded, which is useful, but it does not say whether the input is validated, whether keys are counted at the top level only, what happens on invalid input, or what the return value is.

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?

Two short, front-loaded sentences with no filler. Every word contributes to the tool's purpose or behavior, and the description is appropriately sized for a simple counting operation.

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?

Despite a simple purpose, the tool exposes nine optional parameters and no output schema. The description does not say how to supply the JSON, which parameter to use, or what the count result looks like, leaving the agent to infer these essentials.

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 schema already documents the parameters; this earns the baseline 3. The tool description adds the general purpose but does not map it to the 'json' parameter nor clarify whether the other optional parameters are alternatives or unrelated.

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 uses a specific verb ('Count') and resource ('keys in a JSON object'), and 'Values discarded' adds a concrete behavioral scope. It does not explicitly differentiate from sibling tools like validate-json or domain-shape, but the tool's name and sentence together make its primary function identifiable.

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 on when to use this tool versus alternatives such as validate-json or domain-shape. The description only states what the tool does, with no when-to-use, when-not-to-use, or alternative routing information.

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