ReceiptRail — x402 Delivery Receipts

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

With no annotations provided, the description carries the burden of behavioral disclosure. It states 'Read-only, no cost' and 'always works — the receipt lives on-chain', which informs the agent about safety and reliability. It does not mention failure modes or return format details, but for a read-only tool this is adequate.

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 with zero waste. The first sentence states what is returned, the second explains lookup methods and safety. Critical information is front-loaded and every phrase 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 lists the returned fields, both lookup methods, and discloses read-only status. With no output schema, this is sufficient for an agent to know what to expect. Minor gaps like precedence when both parameters are provided are not addressed, but the tool's simplicity makes this acceptable.

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%, so both parameters have descriptions. The description adds value by explaining that payment_ref is the more reliable lookup method and provides an example format for receipt_id. This goes beyond the schema's basic type descriptions.

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 (Fetch) and resource (full receipt details) and enumerates the specific fields returned (digests, checks, outcome, amount, buyer, seller, timestamp, PDA). This clearly distinguishes it from sibling tools issue_receipt and verify_receipt, which focus on creation and verification respectively.

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 provides clear lookup guidance: use receipt_id or x402_payment_ref, and explicitly notes that payment_ref always works because the receipt lives on-chain. It does not explicitly contrast with siblings, but the purpose is distinct and the usage context is well-defined.

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

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

No annotations provided, so description carries burden. It discloses that it costs 0.001 USDC, requires x402 payment, and returns a payment challenge if signature omitted. However, it does not describe what happens on failure (e.g., insufficient payment, invalid digest), or the exact format of the challenge, though polling behavior is mentioned. Partial disclosure.

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?

Compact two-sentence description that front-loads the core purpose and then explains the payment flow. Good use of parentheses. Slightly dense, but efficient.

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?

For a transactional tool with payment and multiple optional params, description covers the essential flow but misses failure scenarios, return structure details, and any rate limits. Given no output schema and no annotations, there is room for more, but the core usage is covered.

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% and each parameter has a decent description. Description clarifies that x402_payment_signature is optional and its omission triggers challenge issuance, which adds value. But it doesn't elaborate on buyer/seller semantics beyond schema—acceptable given high coverage.

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?

Description clearly states verb 'anchor', resource (SHA-256 digest + x402 settlement reference on Solana), and outputs a permanent publicly verifiable receipt. Differentiates from siblings: get_receipt retrieves, verify_receipt verifies, issue_receipt anchors.

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?

Description explicitly explains when to use: to issue a receipt for delivered content after payment. It also specifies the two-step flow: omit signature to get challenge, then call again with signature. No alternatives mentioned but the usage context is clear and complete.

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

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

With no annotations, the description carries the full burden, and it delivers: discloses read-only nature, no cost, on-chain verification logic, and the fallback lookup behavior. It does not state failure semantics (error vs. boolean result) or return format, which is a minor gap for a verify tool given zero annotation coverage.

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 with zero waste: core verification logic front-loaded, then lookup methods, then a concise safety note. Every sentence earns its place and the most important information appears first.

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?

For a tool with no annotations and no output schema, the description covers verification semantics and lookup well, but does not explain what the agent receives on success or failure, nor whether both parameters can be provided together. This is a meaningful gap for an MCP tool with no structured output contract.

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% and both parameters are well documented in the schema, so the baseline is 3. The description adds the nuance that payment_ref 'always works' and clarifies the relationship between the two lookups, adding marginal value beyond the schema but not compensating for anything missing.

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?

States a specific verb (verify) and resource (AgentToll receipt against live Solana state), then defines what verification means concretely: PDA owner must be the AgentToll program and the stored digest must match. This gives an agent a precise mental model and implicitly differentiates from siblings get_receipt (fetch) and issue_receipt (create).

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?

Provides clear lookup guidance: primary key receipt_id, with payment_ref as the reliable fallback ('always works — the receipt lives on-chain'), reinforced by the schema's 'use this if receipt_id unknown.' However, it does not explicitly state when to choose verify_receipt over get_receipt, leaving the verify-vs-fetch decision to inference.

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