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

With no annotations, the description must disclose behavioral traits itself. It only states 'Values discarded,' which reveals the core behavior but omits critical details: What if input is not a valid JSON object? Does it error? Does it access disk or network? The schema descriptions for parameters are inconsistent (e.g., 'json' says 'validate' while tool says 'count'), adding confusion rather than transparency.

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 only two sentences and is front-loaded with the core purpose. There is no redundant wording. However, the extreme brevity borders on under-specification, but for the metric of conciseness it is efficient and earns its place.

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?

Given 9 parameters, no annotations, and no output schema, the description is severely incomplete. It does not explain how to provide input, what the output is (beyond a count), what constitutes a valid JSON object, or why multiple unrelated parameters exist. An agent cannot reliably call this tool based on the given definition.

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 tool description adds no parameter clarification. The parameter descriptions are vague and sometimes contradictory—e.g., 'ref' says 'discarded after the shape check' and 'json' says 'to validate', which do not align with the tool's stated purpose of counting keys. The description does not indicate which parameter is the primary input, leaving agents unable to construct a correct call.

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 the specific operation: 'Count keys in a JSON object. Values discarded.' This is a clear verb+resource. However, it does not differentiate from sibling tools like validate-json or domain-shape, which also deal with JSON structure. Still, the core purpose is unambiguous.

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?

The description provides no guidance on when to use this tool versus siblings. It does not mention any prerequisites, alternatives, or contextual triggers. An agent has no basis to decide between this and validate-json or other shape-checking tools.

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