Ecosystem Proposal: Typed Settlement Wire Grammar for XRPL Memos (X402-TSWP)

[Synaptics-Lab]

title: Typed Settlement Wire Grammar for XRPL Memos
description: Byte-exact typed memo grammar for payment-gated M2M settlements and UETR tracking on XRPL.
author: Abdul Shabazz  (@veritasvaultone, Synaptics Lab)
category: Ecosystem
status: Proposal
created: 2026-09-26
updated: 2026-09-26

[Ecosystem Proposal: Typed Settlement Wire Grammar for XRPL Memos (X402-TSWP)]

Abstract

This standard specifies an ecosystem wire format for XRP Ledger (XRPL) transaction memos to support autonomous Machine-to-Machine (M2M) payment paywalls, payment-gated API execution, and atomic linkage of cross-border financial identifiers (such as SWIFT gpi UETRs) to on-chain XRPL settlements.
The standard builds upon the IETF X402-TSWP (The X402 Typed Settlement Wire Protocol) specification and standardizes hex-encoded byte-exact discriminators within XRPL Memos arrays.

Motivation

The XRP Ledger is widely utilized for high-throughput, low-latency, and low-cost payments. The XRPL transaction schema provides a native Memos array capable of storing arbitrary hex-encoded data:

• MemoType: Categorizes the purpose of the memo.
• MemoData: Carries the primary memo payload.
• MemoFormat: Designates mime-type or encoding structure.
  However, in the absence of an open ecosystem standard for memo structure:

1. Ad-Hoc String Parsing: Off-chain payment gateways, Model Context Protocol (MCP) tool servers, and automated settlement engines parse free-text memos using brittle, non-standard regular expressions.
2. Missing Challenge Preimage Grammar: Machine-to-machine micropayment clients lack a standardized grammar to associate a payment with an ephemeral HTTP 402 or MCP challenge token.
3. SWIFT / ISO 20022 Disconnect: Financial institutions clearing via XRPL cannot deterministically link on-chain transaction hashes to the SWIFT Unique End-to-End Transaction Reference (UETR) mandated by ISO 20022.
   This proposal defines a canonical, typed schema for XRPL memos to establish interoperability across institutional gateways, AI agents, and cross-chain execution engines.

---

Specification

1. Memo Fields & Hex Encoding

XRPL transactions carrying X402-TSWP payloads MUST format the Memos array entry with the following canonical fields:

Field	Encoding	Plaintext Value	Hex Value
MemoType	Hex (ASCII)	X402 or X402G	58343032 or 5834303247
MemoFormat	Hex (ASCII)	text/plain	746578742f706c61696e
MemoData	Hex (ASCII)	<TypedGrammar>	hex(<TypedGrammar>)

2. Operational Memo Grammar

The MemoData payload follows a strict prefix-based discriminator grammar:
X402<Discriminator>:<Payload>

2.1. Gateway Challenge Payment (X402G)

Used by autonomous AI agents, MCP servers, and HTTP 402 API gateways for single-use challenge satisfaction:

• Format: X402G:<challenge-uuid>
• Length: Exactly 42 ASCII characters (84 hex nibbles).
• Example Plaintext: X402G:827da995-adda-4dd7-9fb5-d05338526873
• Example Hex MemoData: 58343032473a38323764613939352d616464612d346464372d396662352d643035333338353236383733

2.2. Multilateral Netting & SWIFT UETR Settlement (X402W)

Used for institutional settlement binding an on-chain XRPL transaction to a specific clearing window and SWIFT gpi UETR:

• Format: X402W:<window-id>:<uetr-uuid>
• Example Plaintext: X402W:1789860218:c3b29f04-8b65-4f42-b9e7-5735cf572bf1

2.3. Market Maker Escrow Collateral (X402M)

Used to fund and identify deterministic liquidity provision collateral on XRPL:

• Format: X402M:<window-id>:<account-address>
• Example Plaintext: X402M:1789860218:rKmtCQXuZpXWgb7KiwKbiQwJeX6AtbpMtC

---

3. Canonical XRPL Transaction Example

An XRPL Payment transaction fulfilling an X402G challenge for a micro-fee of 160 drops:

{
  "TransactionType": "Payment",
  "Account": "r9LChhKowvV8r...ClientAccount",
  "Destination": "rKmtCQXuZpXWgb7KiwKbiQwJeX6AtbpMtC",
  "Amount": "160",
  "Memos": [
    {
      "Memo": {
        "MemoType": "58343032",
        "MemoFormat": "746578742f706c61696e",
        "MemoData": "58343032473a38323764613939352d616464612d346464372d396662352d643035333338353236383733"
      }
    }
  ]
}
Rationale
Native Field Compatibility: Utilizes existing XRPL transaction primitives without requiring ledger amendments or core rippled modifications.
Byte-Exact Verification: The deterministic length and prefix structure permit fast substring slicing and exact comparison in high-throughput ledger ingest pipelines.
Cross-Chain Equivalence: The X402G and X402W formats are identical across XRPL and Solana SPL Memo v2, enabling uniform verification logic across multi-rail settlement gateways.
Backwards Compatibility
This standard is purely additive and strictly backward-compatible. XRPL accounts, wallets, and explorers that do not implement X402-TSWP continue to process and render transactions normally.

Reference Implementation
Production Node & Gateway: Operating in syn-m2m-server and mcp-402-gateway (:8405) settling transactions on XRPL Altnet.
IETF Specification: Standards Track [draft-shabazz-http-x402-tswp-00](https://datatracker.ietf.org/doc/draft-shabazz-http-x402-tswp/)
.
Defensive Prior Art Registration: Zenodo [DOI 10.5281/zenodo.22979715](https://doi.org/10.5281/zenodo.22979715)
.
Cross-Rail Equivalents: Solana Foundation [SIMD PR #671](https://github.com/solana-foundation/solana-improvement-documents/pull/671)
.
Security Considerations
Single-Use Challenge Enforcement: Gateways MUST invalidate the challenge UUIDv4 immediately upon the first validated ledger appearance to prevent replay attacks.
Strict Memo Equality: Ingesting services MUST verify the full byte-exact memo value (MemoData == hex("X402G:" + challenge)) to eliminate injection of extraneous trailing bytes.
Ledger Validation: Gateways MUST confirm transaction finality in a validated ledger ("validated": true from rippled) before releasing commercial tool execution.