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

With no annotations, the description must carry full behavioral disclosure. It only says 'Values discarded' which hints at behavior, but it does not state the return value (presumably a count), error handling for invalid JSON, or the fact that only the 'json' parameter is used. The schema descriptions for several parameters say 'discarded after the shape check,' which conflicts with the counting purpose, 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 a single concise sentence, which is good for front-loading. But it is under-specified for a tool with nine parameters and no output schema. It omits essential usage context, so while concise, it is not appropriately sized for the complexity.

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 nine optional parameters and no output schema, the description is far too brief. It does not identify which parameter holds the JSON object, what the tool returns, or how it handles invalid input. The inconsistency with schema descriptions further undermines completeness.

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 baseline is 3. However, the description adds no parameter-specific value and fails to clarify that the 'json' parameter is the intended input. Moreover, the schema description for 'json' says 'JSON text to validate,' which contradicts the description's counting purpose. This mismatch actively misleads an agent trying to select parameters.

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.' This is clear about the core action. However, it does not differentiate from sibling tools like validate-json or domain-shape, and it is ambiguous which of the nine parameters actually holds the JSON object.

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 versus alternatives. The description does not mention exclusions, prerequisites, or when to prefer a sibling like validate-json or domain-shape. The agent must infer usage from the tool name alone.

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