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

With no annotations provided, the description fully carries the behavioral disclosure burden. It reveals the internal process (decode header, run 10 rules), the output behavior (first failing rule with fix), and operational constraints (stdlib-only, no network, no install, zero cost). This goes well beyond a minimal statement and gives the agent confidence about side effects and limitations.

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 a dense but well-structured paragraph. It front-loads the core action, lists the rules compactly, and includes the most critical edge case. The parenthetical about price/tier is minor noise but does not detract from the overall efficiency. Every sentence adds value.

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 description covers the tool's purpose, input, process, output, and an edge case, which is comprehensive for a diagnostic tool with no output schema. It leaves a minor ambiguity about what happens when all 10 rules pass (no failing rule), but overall it gives an agent sufficient context to decide when and how to invoke it.

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 enhances understanding by linking the X-PAYMENT header to x_payment_b64 and paymentRequirements to the rules, but it does not add extra per-parameter semantics beyond the schema. It neither compensates nor detracts, hence a solid 3.

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 opens with the specific verb-resource pairing 'Diagnose a failing x402 v2 /verify', which precisely states what the tool does. It further distinguishes itself from sibling tools by detailing the rule-based diagnosis and the output of 'FIRST failing rule with a plain-English fix', making its purpose unambiguous and differentiated.

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?

It clearly states when to use the tool: to diagnose a failing /verify call, especially when a bare HTTP 402 is returned. It does not explicitly mention alternatives or when not to use it, but the scenario-driven guidance is clear and actionable, meriting a score above the 'implied only' level.

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