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

Without annotations, the description must disclose behavior itself, but it only says 'Values discarded.' It does not mention the return format, side effects, or how the JSON is extracted from the input. The lack of any statement about what happens to the key count or whether this is read-only leaves significant behavioral gaps.

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 concise and front-loaded with the main action first. Two short sentences avoid unwanted words, but the brevity leaves out crucial information about which parameter to use, so it is not maximally effective.

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?

Given the complexity of a 9-string-parameter schema and the absence of an output schema or annotations, the description is under-specified. It fails to connect the JSON object to a concrete parameter and does not explain the expected input is a pointer to one of the params. An agent cannot reliably invoke this tool correctly.

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?

With 100% schema description coverage, the baseline is 3. The tool description merely repeats 'Values discarded,' which the schema already conveys indirectly through per-parameter notes like 'discarded after the check.' No additional semantic meaning is added to help agent decide which parameters to provide.

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 verb (count) and resource (keys in a JSON object), but it never clarifies which input property holds that JSON object. The schema has a `json` parameter, yet the presence of eight other optional parameters with domain-specific descriptions makes the intended target ambiguous. This is more specific than a tautology but not enough to confidently select the tool over siblings as a key-counting utility.

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 about when to use this tool over siblings such as validate-json or shape checks, nor any exclusions or context hints. The description doesn't say if this is the right tool for counting keys versus some other aggregation, leaving the agent to guess.

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