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

With no annotations provided, the description carries the full behavioral burden. It does disclose one meaningful trait: values are discarded, so the count is independent of value content. However, it does not state whether nested keys are counted, what happens with invalid JSON, or what the output shape is.

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 and front-loaded, with no wasted words. It is slightly too sparse for a tool with nine optional parameters and no title, but it avoids fluff and each sentence earns its place.

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 no annotations, no output schema, and nine optional parameters, this description is incomplete. It does not say which parameter should contain the JSON, what value is returned, how nesting is handled, or how it differs from validate-json. The 'Values discarded' sentence is helpful but insufficient.

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 clarifies that the operation is counting rather than validating, but it does not explicitly map 'JSON object' to the 'json' parameter. The schema's own description of 'json' as 'JSON text to validate' adds confusion rather than connecting it to key counting.

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 ('Count') and resource ('keys in a JSON object'), and 'Values discarded' further clarifies the operation. It is clear enough to be distinguished from siblings like validate-json by intent, but it does not explicitly name alternatives or describe its exact input parameter.

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 validate-json or other sibling tools, no stated use cases, and no exclusions. An agent must infer applicability solely from the purpose phrase.

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