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

With no annotations, the description carries the full burden. It discloses that values are discarded, but does not state what happens with invalid JSON, what the return value is, or how the other eight parameters affect the behavior. The minimal disclosure is inadequate for a tool with many optional parameters.

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 short but under-specified. While it is front-loaded with the primary action, it omits essential information about usage and parameter mapping. The brevity is not a virtue here; it results in an incomplete and unhelpful tool definition.

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?

The tool has 9 optional parameters, no required ones, and no output schema. The description only covers the core function without explaining the role of the other parameters, expected input format, return value, or error behavior. This is severely incomplete for an agent to call the tool correctly.

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%, but the tool description adds no meaning beyond the schema. The parameter 'json' is described as 'JSON text to validate; discarded after the check', which contradicts the tool's stated purpose of counting keys. The description fails to clarify which parameter carries the JSON object, and the schema descriptions are inconsistent with the tool's behavior.

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 specific verb and resource: 'Count keys in a JSON object.' It clearly distinguishes from siblings like validate-json or domain-shape, but it does not clarify how the JSON object is passed via the parameters, leaving ambiguity about which parameter to use. The core purpose is clear but not fully actionable.

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. It does not mention conditions for use, exclusions, or sibling tools. An agent is left to infer the appropriate context from the name alone, which is insufficient.

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