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

With no annotations provided, the description carries the full burden of disclosure. It reveals that values are discarded and that the tool counts keys, but it remains silent on failure modes (e.g., invalid JSON, non-object input), output format (does it return just a number?), and any side effects. This is only minimal transparency; an agent cannot fully anticipate the tool's behavior based on this description alone.

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, short sentence that gets to the point quickly. However, it lacks structure that connects to the parameter list—there is no mention of how the parameters map to the action, and the return value is not hinted at. It is concise but not well-packaged for an agent to grasp the full interface, especially given the array of parameters.

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?

With 9 parameters, no annotations, no output schema, and a description that addresses only the generic notion of counting keys, this definition is severely incomplete. It provides no explanation of how agents should supply the JSON object (via 'json' parameter? or other parameters that encode a reference?), what the output format is, or how the tool handles edge cases. An agent cannot reliably invoke this tool correctly with the given 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 already has a textual definition. The description 'Count keys in a JSON object' adds the specific action (counting) beyond the schema's generic 'validate' wording for the 'json' parameter, giving agents a more precise expectation. However, the description does not reconcile the other 8 parameters (e.g., 'city', 'query') which are described as being discarded after checks, leaving ambiguity about how they relate to counting. The baseline of 3 is appropriate since the schema handles most semantic load.

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?

States a clear verb ('Count') and specific resource ('keys in a JSON object'), and further clarifies that values are discarded, which distinguishes it from validation tools. However, it does not explicitly differentiate from sibling tools like 'validate-json' or 'domain-shape', and the presence of 9 unrelated-looking parameters (city, query, path, etc.) that the description never addresses muddies the intended scope.

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 provided on when to use this tool, when not to use it, or what alternatives exist. The description is a bare functional statement with no conditions or exclusions, leaving the agent to infer applicability from context alone.

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