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

With no annotations, the description carries the behavioral burden. It discloses a key behavioral trait—values are discarded—which prevents an agent from expecting value preservation. It does not specify return format or nested-key behavior, but for a simple count tool this is mostly sufficient.

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?

Two short, focused sentences with no filler. The core behavior and the important value-discarding caveat are stated directly and front-loaded.

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 is simple and the schema is well documented, but there is no output schema and the description does not explicitly state that a numeric count is returned or how nested keys are handled. The optional-parameter schema partially compensates for the ambiguity, but the description alone is not fully complete.

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 input schema already documents all 9 parameters with 100% coverage, so the baseline is 3. The description adds a global 'values discarded' rule but gives no parameter-specific explanation beyond what the schema already provides.

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 clearly states a specific operation—count keys—and the resource, a JSON object. 'Values discarded' also differentiates it from value-returning or validation tools, though it does not explicitly name or contrast a sibling.

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?

Usage is implied: use when you need a key count and do not need the values. However, there is no explicit when/when-not guidance or mention of alternatives among the many sibling tools.

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