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openfang-rail

by io.github.89rat
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Verify any XDR-1 receipt — free, stateless, any issuer

receipt_verify
Read-onlyIdempotent

Verifies a signed XDR-1 receipt from ANY x402 service: recomputes the canonical digest and recovers the signer, then compares it to the declared signer. Free forever — no account, no quota, no storage (stateless). A valid receipt proves the signer signed that tool call at that timestamp; it does NOT prove funds moved or any business claim.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
receiptYesThe full XDR-1 receipt object: v, tool, tool_version, input_hash, output_hash, payer, recipient, amount, nonce, ts, tier, signer, signature (optional successor/stream_state).

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
scopeNo
validNo
digestNo
canonicalNo
declared_signerNo
signer_recoveredNo

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changed
    • changedInput schema / examples
      Previous value: -[
-  {
-    "receipt": {
-      "amount": "0",
-      "input_hash": "0x…",
-      "nonce": "0x…",
-      "output_hash": "0x…",
-      "payer": "0x…",
-      "recipient": "0x…",
-      "signature": "0x…",
-      "signer": "0x…",
-      "tier": "free",
-      "tool": "iban-check",
-      "tool_version": "1",
-      "ts": 0,
-      "v": "XDR-1"
-    }
-  }
-]New value: +[
+  {
+    "receipt": {
+      "amount": "0",
+      "input_hash": "0x…",
+      "nonce": "0x…",
+      "output_hash": "0x…",
+      "payer": "0xc59c85e661d34084a7769f955d17fd38254a6235",
+      "recipient": "0xc59c85e661d34084a7769f955d17fd38254a6235",
+      "signature": "0x…",
+      "signer": "0xa036e2e3e19c6d02f30b3a9eb0acd057e6d9a5c8",
+      "tier": "free",
+      "tool": "iban-check",
+      "tool_version": "1",
+      "ts": 0,
+      "v": "XDR-1"
+    }
+  }
+]
  2. Added

TDQS

A4.5/5.0
Behavior5/5

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

Beyond the readOnlyHint and idempotentHint annotations, the description adds meaningful behavioral details: the tool is stateless, free, has no quota, and performs no storage. It also discloses the exact verification algorithm and clearly limits the meaning of a valid receipt, preventing over-interpretation of results.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is three sentences with no filler. The first sentence front-loads the primary purpose and algorithm, the second adds operational constraints, and the third sets expectations for what the result means. Every sentence contributes information an agent needs.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the single parameter, full schema coverage, presence of an output schema, and annotations for read-only/idempotent behavior, the description covers all essential context. It explains the verification process, the statelessness, and the semantic limits of the result, leaving no critical gap for correct invocation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the single 'receipt' parameter is already fully documented in the schema, listing all required fields and optional extensions. The tool description adds context about what the tool does with the receipt, but it does not add new parameter-level detail beyond what the schema provides, so baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource — 'verifies a signed XDR-1 receipt' — and explains exactly how verification works: recomputing the canonical digest, recovering the signer, and comparing it to the declared signer. It clearly distinguishes this from sibling format checks like iban_check or luhn_check by emphasizing ANY x402 service and the cryptographic nature of the receipt.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides clear context for when to use the tool: verifying a signed XDR-1 receipt from any x402 service, with no account, quota, or storage required. It also explicitly states a when-not: it does NOT prove funds moved or any business claim. However, it does not name any alternative tools or more explicitly contrast this with related payment/verification tools.

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

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