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

Annotations say readOnlyHint=false and idempotentHint=false, and the description supplies the reason those are true: each call costs $0.005 USDC and the first attempt returns a PaymentRequired challenge rather than a result. That is real behavioral context an agent cannot derive from the annotations. It stops short of stating error behavior for malformed JSON or any input size limits.

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?

Three compact clauses ordered by importance: what it does, what it costs, how to pay, plus an HTTP fallback. Every sentence carries information and the purpose is front-loaded. The HTTP equivalent URL is marginally beyond what an MCP caller needs but is cheap and useful for debugging.

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?

With no output schema, the description should say what comes back (a formatted JSON string? an object?) and what happens when the input is not valid JSON — it says neither. The paid-API mechanics are well covered, but the result contract for a simple one-parameter tool is left implicit.

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?

There is a single parameter 'text' at 100% schema description coverage, so the schema carries the burden and baseline is 3. The description adds no detail about whether 'text' must already be valid JSON, what encoding is expected, or how large it may be.

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 first sentence gives a specific verb pair and resource: 'Format and prettify a JSON document.' An agent immediately knows the operation. It does not differentiate from the obvious sibling devutils_json_validate, so an agent choosing between formatting and validating must infer the distinction from the names alone.

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 spends its space on the payment procedure (call without payment, get a challenge, retry with _meta["x402/payment"]) rather than on when to use this instead of devutils_json_validate or devutils_csv_to_json. Usage is implied by the verb, and the payment protocol is genuinely necessary call guidance, but the selection guidance between siblings is absent.

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