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

With no annotations, the description carries the full burden of disclosing behavior. It states that values are discarded, which is useful, but it does not say what the tool returns, whether it counts top-level keys only or nested keys, or what happens for invalid JSON. This is insufficiently transparent for a tool with no output schema.

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 concise and front-loaded: the core operation is in the first sentence and the key constraint in the second. Every word earns its place, though the brevity comes at the cost of important missing detail.

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 seven optional parameters, no required fields, no output schema, and many siblings, the description is not complete enough for reliable invocation. It should specify the target parameter, the return value, and how nested keys are counted.

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?

Although schema coverage is 100%, the description does not identify which parameter supplies the JSON object among seven optional parameters. The schema's 'json' field is described as text to validate, not text to count, and no other parameter connects to counting keys. The description adds no disambiguation for parameter selection.

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 concrete action ('Count keys') and a resource ('a JSON object'), and the phrase 'Values discarded' clarifies that the count is key-only. It is not a tautology and is broadly distinguishable from siblings like validate-json, but it does not explicitly differentiate itself or mention the relevant input parameter.

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 about when to use this tool versus validate-json, hn-front-count, or other sibling tools. The intended use is only weakly implied by the description, with no mention of alternatives, exclusions, or prerequisites.

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