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

With no annotations, the description carries the behavior burden; 'Values discarded' is a useful disclosure that the tool ignores value content. But it does not say whether the count is distinct keys, nested keys, or just top-level, nor does it describe side effects or the return format.

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; the core operation is front-loaded and the 'Values discarded' qualifier earns its place by communicating a meaningful behavioral trait.

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?

This tool has multiple optional parameters, no output schema, and no annotations. The description does not explain the return value, how the JSON object is supplied, or how nested objects are handled, leaving a material gap for an agent attempting invocation.

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%, but the schema descriptions do not support the described purpose: 'json' is described as 'JSON text to validate', not as the object whose keys are counted, and the other parameters look unrelated. The description adds no mapping from 'a JSON object' to an input parameter, so an agent cannot confidently choose the right argument.

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 names a specific operation ('Count keys') and a specific resource ('a JSON object'), and adds that values are discarded, which distinguishes the tool from value-oriented JSON tools like validate-json. It is not a tautology, but it does not explicitly position the tool against its siblings.

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 use case is implied: call this when you need to know how many keys a JSON object has and do not care about its values. However, there is no explicit statement of when not to use it or which sibling alternative, such as validate-json, might be preferable.

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