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

The description does add one behavioral trait beyond the tool name: 'Values discarded' tells the agent that values are ignored. But with no annotations provided, the description carries the full burden and still leaves key behavior unspecified, such as whether nested keys are counted, what the return value looks like, and whether there are side effects.

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, and the core operation is front-loaded. Every word contributes to the meaning, making it appropriately concise.

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 nine optional parameters, no output schema, and no annotations, this description is too thin. It does not explain whether to supply one parameter, several, or a JSON string, nor does it specify whether the count includes nested keys or returns a simple integer. An agent could easily invoke it incorrectly.

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 main description adds the useful semantic that values are irrelevant and discarded, but it does not clarify how the nine optional string parameters relate to 'a JSON object' or whether the tool counts keys in its own input object versus a JSON text value.

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', and a specific resource, 'JSON object', and adds that values are discarded. This makes it distinguishable from counting tools like sentence-count, though it does not explicitly differentiate itself from shape-validation siblings or clarify that the input object itself is the JSON object being counted.

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 intended usage is implied: use this when you need the number of keys in a JSON object. However, there is no explicit when-to-use/when-not-to-use guidance, no prerequisites, and no mention of alternatives such as validate-json, so an agent must infer the routing.

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