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

With no annotations, the description carries the behavioral disclosure burden. 'Values discarded' is a useful disclosure that values are ignored and not used. But it does not mention side effects, return value, or behavior with an empty object or missing keys.

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?

Two short sentences, front-loaded with the core operation and no filler. 'Values discarded' earns its place by clarifying scope.

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 9-parameter tool with no annotations and no output schema, this is under-specified. It does not clarify what the returned count represents, whether all schema keys are counted or only supplied keys, or how to pass the JSON object. The rich sibling list only makes the missing positioning more noticeable.

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 coverage is 100%, so a baseline of 3 is warranted, but the description creates a mismatch: it refers to a JSON object while the schema only exposes nine flat string properties and no object parameter. The candidate 'json' parameter is described as JSON text to validate, which points to validation rather than counting. The description adds no guidance on which parameters to supply.

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 uses a specific verb and resource ('Count keys in a JSON object') and adds a meaningful qualifier ('Values discarded'). It is clearly distinguishable from sibling tools like validate-json, which validates rather than counts. However, it does not explicitly connect the 'JSON object' to the actual input parameters.

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 when-to-use or when-not-to-use guidance is provided. The description does not mention alternatives or explain when counting keys would be preferable to validation or other sibling operations.

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