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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It adds 'Values discarded' and 'JSON object' context, but fails to explain why the tool accepts nine unrelated string parameters or what happens to them, and it doesn't disclose return format or failure behavior. The schema hints these inputs are 'discarded,' which conflicts with the described purpose of counting keys, leaving the actual behavior ambiguous.

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 the core purpose front-loaded and zero filler. It is appropriately brief, though the brevity comes at the cost of missing usage and parameter guidance.

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 9 parameters, no annotations, and no output schema, the description is inadequate. It never specifies which parameter carries the JSON, what the other eight parameters do, or what the count result looks like. An agent cannot confidently map inputs to the described behavior.

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, but the description adds no value about how any parameter relates to the counting operation. The schema's own descriptions ('discarded after the shape check', 'no disk access') suggest most inputs are unused, and the description fails to clarify which parameter is the JSON object to count, creating confusion rather than resolving it.

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 and resource ('Count keys in a JSON object') and distinguishes itself from length-checking siblings like search-query-len. However, the 9 input parameters (ref, url, city, feed, host, zone, query) appear entirely unrelated to counting keys in a JSON object, and no parameter clearly holds the JSON to inspect, which muddies 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?

There is no guidance on when to use this tool versus alternatives. It never references validate-json, search-query-len, or any sibling, nor does it state conditions that should route an agent here. The intended use case is left entirely to inference.

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