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

No annotations are present, so the description carries the behavioral burden. It directly discloses that values are discarded, which is a meaningful behavioral trait beyond merely counting keys. It does not describe the return format or invalid-input behavior, but the core side-effect is clear.

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 sentences, front-loaded with the action ('Count keys') and immediately followed by the critical caveat ('Values discarded'). Every sentence earns its place and there is no wasted text.

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 simple counting tool this is minimally viable, but with no annotations and no output schema the description omits the return type and what happens if no keys are present. The presence of many loosely related parameters also makes it less obvious that the input object itself is what gets counted.

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 coverage is 100%, so the baseline is 3 and the schema already documents each parameter. The description's 'Values discarded' globally clarifies that parameter values are irrelevant to the count, which adds some meaning, but it does not explain which parameter holds the object to count or how the key count is derived.

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 action and resource: 'Count keys in a JSON object.' The second sentence, 'Values discarded,' adds the key boundary of what the tool does not do. This is clearly distinct from siblings like validate-json or hn-front-count.

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 description implies the tool should be used when only the number of keys matters and values are irrelevant, but it never states when not to use it or names an alternative. There is no explicit steering toward or away from sibling tools.

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