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

With no annotations provided, the description carries the full burden of behavior disclosure. 'Values discarded' is a meaningful behavioral trait: it tells the agent that parameter values are irrelevant and only key presence matters. It does not explain the output format or whether counting is recursive, but it does disclose the key behavioral quirk.

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. 'Count keys in a JSON object' is front-loaded, and 'Values discarded' is a concise, high-value behavioral qualifier.

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?

The description is adequate for a simple counting operation, but the lack of an output schema and the presence of many unrelated-looking parameters leave some ambiguity about whether the input object is the argument object itself or a JSON string supplied via a parameter. No annotations help close that gap.

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 coverage is 100%, so the baseline is 3, but the description adds important global semantics: despite the nine heterogeneous parameters, their values are all discarded. This helps an agent avoid being misled by the individual parameter descriptions and focus on key presence instead.

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 operation: count keys in a JSON object, and adds a distinctive detail: values are discarded. It is specific and useful, but it does not explicitly differentiate this tool from siblings such as validate-json or other shape-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?

The description implies when to use the tool: whenever you need the number of keys in a JSON object. It does not provide explicit when-not-to-use guidance or name alternatives, so the usage context is only implied.

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