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

With no annotations, the description carries the full burden of behavioral disclosure. 'Values discarded' is a meaningful behavioral trait that tells the agent parameter content is irrelevant, but it does not say whether keys are counted only at the top level, what the return value looks like, or whether any external access occurs.

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 short sentences and every word earns its place. The core operation is front-loaded, and 'Values discarded' is a concise, high-value clarification with no redundancy.

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, no annotations, and no output schema, the description is under-specified. It omits the return format, how to map the 'JSON object' to the schema properties, and any practical example or boundary condition, leaving too much for the agent to infer.

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. The description adds that values are discarded, which is useful because the nine parameters have semantically meaningful descriptions in the schema, but it still does not clearly explain that the parameters themselves are the keys being counted.

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 names a specific operation, 'Count keys', and a clear resource, 'a JSON object', while adding that values are discarded. This is distinct from the sibling validators and fetch tools, though it does not say whether the counted object is the tool's own arguments object or a separate JSON document.

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 instead of siblings like validate-json or search-query-len. No alternatives, exclusions, or prerequisite conditions are mentioned, so an agent must infer usage entirely from the one-line purpose.

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