Purpose
Specifications in this section:- Define normative behavior using precise, unambiguous language
- Follow RFC 2119 conventions for requirement levels (MUST, SHOULD, MAY)
- Include data structures with exact field definitions and types
- Document protocol flows with sequence diagrams and state transitions
- Specify error handling and edge cases
Audience
These specifications are written for:- Protocol implementers building x402 facilitators or clients
- SDK developers creating libraries that interact with Nevermined
- Integration engineers connecting existing systems to Nevermined
- Security auditors reviewing protocol designs
Relationship to Other Documentation
| Documentation Type | Purpose |
|---|---|
| Getting Started | Quickstart guides and tutorials |
| Use Cases | Business scenarios and solution patterns |
| Integration Guides | Step-by-step implementation instructions |
| API Reference | SDK methods and REST endpoints |
| Specifications | Formal protocol definitions (this section) |
Conventions
Requirement Levels
This documentation uses RFC 2119 terminology:- MUST / REQUIRED / SHALL — absolute requirement
- MUST NOT / SHALL NOT — absolute prohibition
- SHOULD / RECOMMENDED — there may be valid reasons to ignore, but implications must be understood
- SHOULD NOT / NOT RECOMMENDED — there may be valid reasons to do this, but implications must be understood
- MAY / OPTIONAL — truly optional behavior
Data Types
- JSON structures use TypeScript-style type annotations
- Hexadecimal values are prefixed with
0x - Base64 encoding uses standard alphabet with
=padding - Timestamps use ISO 8601 format unless otherwise specified
Available Specifications
x402 Smart Accounts Extension
Extends x402 with ERC-4337 smart accounts, session keys, and programmable smart contract settlement
x402 Visa VIC Extension
Extends x402 with Visa Intelligence Commerce (VIC) and Visa Token Service (VTS) for fiat payments