acp-extensions-authoring

acp-extensions-authoring is a skill for Claude Code from OrcaQubits/agentic-commerce-skills-plugins. It costs 44 tokens per session (785 once invoked), scanned A, original, MIT.

A guide for creating optional ACP protocol extensions, which are add-ons that add fields or behavior without changing the core protocol. It covers where new data belongs, how schemas are composed, and how extensions are versioned.

In plain words
What is it for?
Use it to build a proprietary or domain-specific ACP feature beyond the built-in extensions.
Why use it?
It gives domain-specific features their own structure and release cycle, reducing the need to change or overload the core checkout design.

Skill for Claude Code

Written for Claude Code: allowed-tools in frontmatter.

Part of the acp-agentic-commerce plugin — 15 skills, 1 agent shipped together

Good fit Use it to build a proprietary or domain-specific ACP feature beyond the built-in extensions.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/orcaqubits/agentic-commerce-skills-plugins/acp-extensions-authoring
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add OrcaQubits/agentic-commerce-skills-plugins --skill acp-extensions-authoring
Clone the repo
git clone --depth 1 https://github.com/OrcaQubits/agentic-commerce-skills-plugins

Made for: Claude Code.

Or install acp-agentic-commerce, the plugin that ships this one along with the rest of its 15 skills, 1 agent.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for acp-extensions-authoring

README.md
[![agentmods](https://agentmods.dev/badge/skills/orcaqubits/agentic-commerce-skills-plugins/acp-extensions-authoring/github.svg)](https://agentmods.dev/skills/orcaqubits/agentic-commerce-skills-plugins/acp-extensions-authoring)
Your own site
<a href="https://agentmods.dev/skills/orcaqubits/agentic-commerce-skills-plugins/acp-extensions-authoring"><img src="https://agentmods.dev/badge/skills/orcaqubits/agentic-commerce-skills-plugins/acp-extensions-authoring/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for acp-extensions-authoring

Your own site · 80×15
<a href="https://agentmods.dev/skills/orcaqubits/agentic-commerce-skills-plugins/acp-extensions-authoring"><img src="https://agentmods.dev/badge/skills/orcaqubits/agentic-commerce-skills-plugins/acp-extensions-authoring.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 44 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 785 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00044 $0.00785
Opus 5 $0.00022 $0.00392
Sonnet 5 $0.00009 $0.00157
Haiku 4.5 $0.00004 $0.00078

Measured 9d ago against content hash b80f4d69b254, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

acp-extensions-authoring scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 9d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

acp-agentic-commerce/skills/acp-extensions-authoring/SKILL.md · 90 lines

How it starts

The opening of the file, as written. The whole thing — 90 lines — stays where its author put it; the contents beside it link to each section on GitHub.

ACP Custom Extension Authoring

Before writing code

Fetch live docs:

  1. Web-search site:github.com agentic-commerce-protocol rfcs extensions for the extensions framework RFC
  2. Web-search site:github.com agentic-commerce-protocol examples for extension examples
  3. Fetch https://developers.openai.com/commerce/specs/checkout/ for how extensions integrate with checkout
  4. Study the built-in discount extension as a reference: web-search site:github.com agentic-commerce-protocol rfcs discount_extension

Conceptual Architecture

What Extensions Are

Extensions are composable, optional add-ons that augment ACP's core capabilities. They allow the protocol to grow without bloating the core spec — new features are added as extensions with independent lifecycles.

Extension Properties

Every extension defines:

  • Name — Core extensions use simple names (discount); third-party use reverse-domain (com.example.loyalty)
  • Version — Calendar versioned (YYYY-MM-DD)
  • Parent capabilityextends field linking to the parent (e.g., extends checkout)
  • JSONPath targets — Where in the core schema this extension adds fields
  • Schema — JSON Schema for the extension's data

JSONPath Targeting

Extensions use JSONPath (RFC 9535) to inject fields into core schema locations:

  • $.CheckoutSessionCreateRequest.discounts — Add fields to the create request
  • $.CheckoutSession.discounts — Add fields to the response
  • Multiple targets per extension are allowed

Extension Lifecycle

draft → experimental → stable → deprecated → retired
  • draft — In development, not for production
  • experimental — Available for testing, may change
  • stable — Production-ready, backwards-compatible changes only
  • deprecated — Still functional, but replacement available
  • retired — No longer supported

Schema Composition Rules

  • Extension schemas are composed alongside (not inside) core schemas
  • Extensions must not conflict with core fields
  • Extensions must not introduce authentication bypasses
  • Extension data follows the same PCI/PII rules as core fields
  • Extensions can reference other extensions (dependency chain)

Read the full file on GitHub · 90 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 9d ago First seen · 90 lines · 44 tokens per session scan A b80f4d69b254

Subscribe to this mod's changes

acp-extensions-authoring is a skill published in the GitHub repository OrcaQubits/agentic-commerce-skills-plugins (39 stars, last pushed 3mo ago), licensed MIT. It adds 44 tokens to every session and 785 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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