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

With no annotations present, the description carries the full behavioral burden, but it only discloses that values are discarded. It does not say whether the tool has side effects, whether it needs any permissions, or how it handles invalid input. The concise note adds a small insight, but important behavior remains undocumented.

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 extremely concise, using two short sentences with no fluff. Each sentence contributes useful information (purpose and a behavioral detail) without redundancy. The structure is front-loaded and easy to skim.

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?

Despite its simple goal, the tool has 9 parameters, no output schema, and no annotations. The description is far too terse to explain which parameter is the JSON object, what the return value looks like, or how to distinguish it from validate-json. Given the complexity, this is an incomplete specification.

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?

The schema descriptions cover all 9 parameters, which raises the baseline to 3 because parameters are already individually documented. The description does not add extra clarity about which parameter to use, e.g., pointing to the JSON string field. Given the confusion caused by eight unrelated parameters listed, a 3 is fair but not generous.

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 action ('Count keys') on a specific resource ('JSON object'), so the tool's basic function is clear. It does not explicitly differentiate it from sibling tools like validate-json, but the semantic difference is evident enough on its own. The odd mismatch with the large parameter schema however leaves ambiguity about what input is consumed.

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, when not to, or how it relates to validators/other count tools. No alternative tools are mentioned, and there is no practical usage context such as prerequisites or intended scenarios. The reader is left to infer the use-case from the name alone.

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