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

With no annotations, the description must disclose behavioral traits itself. It only mentions 'Values discarded', but does not explain whether JSON validation occurs, what happens with invalid JSON, whether only top-level keys are counted, or the output format. It is too sparse to give an agent confidence in the tool's behavior.

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 very concise—two short sentences with no fluff. It is front-loaded with the core function. However, it is perhaps too terse, omitting critical context like parameter usage, which reduces its effectiveness.

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?

Given the complexity (9 parameters, no required fields, no output schema), the description is severely incomplete. It does not explain the relationship between the parameters and the counting operation, nor does it describe the return value. An agent would struggle to call this tool correctly without external knowledge.

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?

Although the schema descriptions cover 100% of parameters, they are mismatched with the tool's purpose. For example, the 'json' parameter is described as 'JSON text to validate', which conflicts with the tool's function of counting keys. The tool description does not clarify which parameter holds the JSON input, so the meaning of parameters remains unclear.

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 clearly states the verb 'Count' and the resource 'keys in a JSON object', which is a specific and useful purpose. However, it does not specify which input parameter provides the JSON, and it does not differentiate from sibling tools like validate-json, so the clarity is slightly diminished.

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. The description does not mention any exclusions, prerequisites, or how it differs from similar tools such as validate-json. An agent has no context to choose this tool over siblings.

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