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

With no annotations, the description carries the full burden. It discloses that values are discarded, but it does not state whether the count is top-level only, what the return value looks like, or whether there are any side effects. The 'values discarded' note is useful but minimal.

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 two short sentences with no filler. The core action is front-loaded and the value-discarding behavior 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?

Despite its brevity, the tool has nine optional parameters, no output schema, and no annotations. The description does not say that the input object itself is presumably the JSON object being counted, nor does it clarify what a caller should pass to get a useful result. For an agent to invoke this correctly, too much is left ambiguous.

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 every parameter has a schema description, those descriptions read like snippets from unrelated tools (city, feed, zone, query) and do not explain how any of them relate to counting keys in a JSON object. The 'json' parameter is described as 'JSON text to validate', not as the object whose keys should be counted, so the schema does not actually clarify invocation.

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 operation: count keys in a JSON object, with the notable behavioral note that values are discarded. This is clear enough to distinguish the tool's core action from most siblings, though it does not explicitly differentiate it from other JSON- or count-related tools.

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 about when to use this tool versus alternatives such as validate-json or other shape-checking siblings. The description does not explain why one would want to count keys, what kind of JSON object is expected, or how the nine optional parameters should be chosen.

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