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

With no annotations present, the description carries the full burden of behavioral disclosure. It does state that values are discarded, which adds some transparency about side effects, but it does not disclose how invalid JSON is handled, whether any of the other optional parameters matter, or what the return value represents beyond counting.

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 only two short sentences and each one contributes: the first says the core action and the second says values are ignored. It is appropriately front-loaded and contains no filler, making it efficient despite its limitations.

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 nine optional parameters, no annotations, and no output schema, this description is insufficient. It does not explain how to pass the JSON object, whether any parameter is actually needed, or what the output represents. This ambiguity would make correct invocation much harder for an agent.

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 descriptions already cover 100% of the parameters, which sets a baseline of 3 even though the tool description itself adds almost no parameter-level meaning. The best candidate parameter, 'json', is described as 'JSON text to validate' rather than 'JSON object to count', so the description's intent is not strongly reinforced by the schema.

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 action ('Count keys') on a specific resource ('JSON object') and adds that values are discarded, distinguishing it from validation-focused siblings like validate-json. However, it does not connect this purpose to any of the nine optional schema parameters, so a full understanding still requires guessing which field is the actual input.

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?

No guidance is given on when to use this tool versus alternatives, nor when to avoid it. The agent is left to infer from the phrase 'Count keys' and the sibling name 'validate-json' that one is about counting and the other about validation, but that is not stated.

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