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

With no annotations provided, the description must carry the full burden of behavioral disclosure. It only says 'Values discarded,' which hints at non-persistence but does not address side effects, permissions, rate limits, or the return format. For a tool with nine optional parameters and no output schema, this is severely lacking.

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 (one sentence), which is positive, but it is too sparse to be useful. It lacks structure or prioritization of key information, and the single sentence does not earn its place by providing actionable details—it merely restates the obvious.

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 tool has nine parameters, all optional, no output schema, and no annotations. The description provides almost no contextual information: it does not explain what the output looks like, when to use this tool, how the parameters relate to the JSON object, or any operational constraints. This is completely inadequate for an agent to call the tool correctly.

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?

The schema provides 100% parameter descriptions, so the baseline is 3, but the tool description does not connect these parameters to the stated purpose of counting keys. The parameter descriptions mention 'shape check' and 'discarded,' which do not align with 'Count keys in a JSON object,' leaving the agent unable to understand how to use the parameters meaningfully. The description adds no extra semantic value beyond 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 verb ('Count') and resource ('keys in a JSON object'), so it is not a pure tautology. However, it fails to differentiate from sibling shape-check tools like validate-json or domain-shape, and the tool's nine parameters (ref, url, city, etc.) are not explained in relation to counting keys, creating confusion about what the tool actually operates on.

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. There is no mention of preferred scenarios, exclusions, or comparisons to sibling tools like validate-json or web-fetch. The description is a single sentence with no usage context.

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