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Guidelines for authoring x402 specification files. Use when writing or proposing a new x402 spec, such as a per-network scheme spec (scheme_<name>_<chain>.md).

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Source SKILL.md: https://github.com/x402-foundation/x402/blob/HEAD/.agents/skills/authoring-specs/SKILL.md

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Authoring x402 specs

Guidance for writing x402 specification files under specs/. Use RFC-2119 keywords for normative statements (MUST / MUST NOT, SHOULD / SHOULD NOT, MAY).

General rules

These apply to every spec type (scheme, extension). The references below add type-specific detail.

Naming

  • Name schemes and extensions in lowercase, hyphen-separated kebab-case (e.g. batch-settlement, offer-receipt), never camelCase.

Protocol version, networks, and units

  • Target protocol v2 only: x402Version: 2, the amount field (not v1's maxAmount), and the PAYMENT-REQUIRED / PAYMENT-SIGNATURE / PAYMENT-RESPONSE headers (not v1's X-PAYMENT / X-PAYMENT-RESPONSE). See the v1 to v2 migration guide.
  • Use canonical CAIP-2 network notation (e.g. eip155:84532, not base-sepolia).
  • Use atomic units for all amounts.

Wire format

  • Be transport agnostic: specify message contents, not how a particular transport carries them.
  • Reference core types (PaymentRequirements, PaymentPayload, SettlementResponse) from x402-specification-v2.md.
  • Every field a spec defines on the wire must be consumed by a downstream role. Do not include human-readable or otherwise purely informational fields.
  • Reuse field names, patterns, and conventions established by existing specs instead of coining new ones.

References