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

No annotations are provided, so the description carries the full burden. It does disclose the key behavioral fact — only the key count is produced, and values are discarded — which is genuine transparency beyond the name. However, it says nothing about behavior on malformed JSON, counting scope (top-level vs. nested keys), resource limits, or failure modes, so it is adequate but gapped.

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?

Eight words, first word is the verb, both sentences earn their place: the first states the operation and the second states the output guarantee. There is no padding or repetition of schema information.

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 optional parameters, no output schema, and no annotations, the description is too thin. It never says how the count is computed (top-level keys only?), what happens on invalid JSON, or which of the nine parameters actually receives the JSON object. An agent would be left guessing about the input contract despite the clean purpose statement.

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. The description adds real meaning beyond the schema: the generic 'json' parameter is described purely as 'JSON text to validate; discarded' in the schema, while the description clarifies that the input is an object whose keys are counted and whose values are dropped. It gives the agent the semantic key needed to select the right parameter among the nine.

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' — with an extra qualifier that values are discarded. It is clear on the face, and 'count keys' distinguishes it from siblings like validate-json and the various shape-check tools, but it never names an alternative or explicitly contrasts itself, so it stops short of a 5.

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 siblings such as validate-json, domain-shape, or search-query-len. No use case, no exclusions, and no alternative is mentioned; an agent must infer placement from the verb alone.

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