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.
npx skills add OrcaQubits/agentic-commerce-skills-plugins --skill acp-capability-negotiationgit clone --depth 1 https://github.com/OrcaQubits/agentic-commerce-skills-pluginsWrote 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.
[](https://agentmods.dev/skills/orcaqubits/agentic-commerce-skills-plugins/acp-capability-negotiation)<a href="https://agentmods.dev/skills/orcaqubits/agentic-commerce-skills-plugins/acp-capability-negotiation"><img src="https://agentmods.dev/badge/skills/orcaqubits/agentic-commerce-skills-plugins/acp-capability-negotiation/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.
<a href="https://agentmods.dev/skills/orcaqubits/agentic-commerce-skills-plugins/acp-capability-negotiation"><img src="https://agentmods.dev/badge/skills/orcaqubits/agentic-commerce-skills-plugins/acp-capability-negotiation.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00043 | $0.00751 |
| Opus 5.5 | $0.00017 | $0.00300 |
| Sonnet 5.5 | $0.00009 | $0.00150 |
| Haiku 4.5 | $0.00004 | $0.00075 |
Grade A, and why
acp-capability-negotiation 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 1mo 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.
How it starts
The opening of the file, as written. The whole thing — 76 lines — stays where its author put it; the contents beside it link to each section on GitHub.
ACP Capability Negotiation
Before writing code
Fetch live docs:
- Web-search
site:github.com agentic-commerce-protocol rfcs capability_negotiationfor the capability negotiation RFC - Fetch
https://developers.openai.com/commerce/specs/checkout/for how capabilities appear in checkout requests/responses - Web-search
site:github.com agentic-commerce-protocol spec json-schema capabilitiesfor the capabilities JSON schema
Conceptual Architecture
What Capability Negotiation Does
ACP agents and merchants may support different features. Capability negotiation allows them to dynamically discover what they both support, so the session uses only mutually available features.
How It Works
- Agent sends capabilities — In the
createrequest, the agent includes acapabilitiesobject listing what it supports - Merchant responds with capabilities — The merchant intersects with its own capabilities and returns what's active for this session
- Intersection governs the session — Only mutually supported features are used
Capabilities Object Structure
The capabilities object contains:
capabilities— Major features (checkout, orders, etc.)extensions[]— Optional add-ons (discount, intent traces, affiliate attribution)payment_handlers[]— Supported payment methodsinterventions— Structured object with sub-fields:supported,required,enforcement,display_context,redirect_context,max_redirects,max_interaction_depth
Extension Pruning
Extensions declare a parent capability via extends. If the parent capability is not in the negotiated intersection, the extension is automatically pruned — no extra logic needed.
Interventions
Interventions are actions that require human involvement. They are represented as a structured object (not a flat array) with sub-fields including supported, required, enforcement, display_context, redirect_context, max_redirects, and max_interaction_depth.
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.
- 1mo ago First seen · 76 lines · 43 tokens per session scan A 29bc428e76c5
acp-capability-negotiation is a skill published in the GitHub repository OrcaQubits/agentic-commerce-skills-plugins (40 stars, last pushed 1mo ago), licensed MIT. It adds 43 tokens to every session and 751 once invoked, about $0.0002 per session on Opus 5.5. 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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