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

No annotations are provided, so the description discloses the key side effect ('mark the session fulfilled') and the return behavior. Yet it omits prerequisites (e.g., prior payment_required call), idempotency, or reversibility, leaving gaps for an agent.

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 sentences, each earn its place: action, trust principle, and return/error behavior. No wasted words; front-loaded with the core purpose.

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?

Without an output schema, the description specifies return shape ({ status: 'fulfilled', resource }) and error cases (not yet paid/expired). It covers the essential behavior but lacks guidance on when to use this vs. payment_status, leaving slight ambiguity.

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 coverage is 100% with clear descriptions for both parameters (payment_id, tx_hash). The tool description does not add extra semantics beyond what the schema already conveys, so a baseline of 3 is appropriate.

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 clearly states the tool verifies a x402 payment on-chain (USDC transfer to your address, exact amount) and marks the session fulfilled. It distinguishes from sibling payment tools by emphasizing on-chain verification as the sole source of truth.

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 provides context that the blockchain is the only trusted source and the payment_sessions table is never trusted alone, implying this tool is for authoritative on-chain verification. However, it does not explicitly contrast with payment_status or payment_required.

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