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

With no annotations, the description carries full burden. It discloses a key behavioral trait: 'The body is discarded.' This tells the agent the tool is stateless (no persistence or side effects on the input), which is valuable information beyond the bare validation action. It could add more about whether it logs or errors, but the discard statement is already strong.

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 sentences, zero waste. The core purpose is first, followed by an important side-effect disclosure. Every word earns its place.

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 has no output schema, so the description should state what the validation returns (e.g., boolean, error code), but it does not. Furthermore, the 4-parameter schema includes three completely unrelated params and the description does not explain their role or how the tool interprets them, leaving an agent with unresolved confusion about a simple validator.

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?

Despite 100% schema coverage, the schema contains three parameters (url, host, zone) that describe URL/host/timezone operations irrelevant to JSON validation, and one 'json' parameter that matches the tool's purpose. The description only says 'a body' and does not clarify whether url/host/zone are ignored, required, or apply to a different mode. This creates serious ambiguity for an agent trying to populate the request, so the description fails to add corrective meaning.

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: 'Check whether a body is valid JSON.' This clearly distinguishes it from the sibling tools, which are all URL/timezone operations (normalize-url, timezone, status), making its purpose unambiguous.

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 exact use case is obvious: use this tool when you need to verify if a JSON string/body is syntactically valid. Though it doesn't explicitly name alternatives, no sibling overlap exists, so the clear context is sufficient. It lacks an explicit 'when-not-to-use' statement, but the purpose is specific enough to make the guidance clear.

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