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agents-at-scale-ark: Skill for Claude Code

.claude/skills/a2a-protocol/SKILL.md

a2a-protocol is a skill for Claude Code from mckinsey/agents-at-scale-ark. It costs 68 tokens per session (2,219 once invoked), scanned A, original, Apache-2.0.

A reference guide for A2A, an open standard that lets separate AI agents discover each other and exchange tasks and messages.

In plain words
What is it for?
It is for building A2A clients and servers, configuring Ark A2A resources, and working with tasks, streaming, and agent descriptions.
Why use it?
It explains the protocol details needed to connect independent agents and diagnose communication problems.

Skill for Claude Code

Written for Claude Code: allowed-tools in frontmatter.

This is mckinsey/agents-at-scale-ark's own configuration. It tells Claude Code how to work on agents-at-scale-ark itself, so it is not a mod to install elsewhere. Copy it as a starting point and replace the rules that are about this project. Everything agents-at-scale-ark configures →

not rated 434repo +1 yesterday A scan SkillSpector: pass 68 tokens original Apache-2.0
View source ↗ mckinsey/agents-at-scale-ark mckinsey.github.io
Reuse

Borrowing it

Nothing to install: this file belongs to mckinsey/agents-at-scale-ark. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file
curl -O https://raw.githubusercontent.com/mckinsey/agents-at-scale-ark/main/.claude/skills/a2a-protocol/SKILL.md
Clone the repo
git clone --depth 1 https://github.com/mckinsey/agents-at-scale-ark

Made for: Claude Code.

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 a2a-protocol

README.md
[![agentmods](https://agentmods.dev/badge/skills/mckinsey/agents-at-scale-ark/a2a-protocol/github.svg)](https://agentmods.dev/skills/mckinsey/agents-at-scale-ark/a2a-protocol)
Your own site
<a href="https://agentmods.dev/skills/mckinsey/agents-at-scale-ark/a2a-protocol"><img src="https://agentmods.dev/badge/skills/mckinsey/agents-at-scale-ark/a2a-protocol/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 a2a-protocol

Your own site · 80×15
<a href="https://agentmods.dev/skills/mckinsey/agents-at-scale-ark/a2a-protocol"><img src="https://agentmods.dev/badge/skills/mckinsey/agents-at-scale-ark/a2a-protocol.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 68 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,219 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. Third-party audits
  • NVIDIA SkillSpector pass 7 Sept 2026
How audits are shown
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 $0.00068 $0.02219
Opus 5.5 $0.00027 $0.00888
Sonnet 5.5 $0.00014 $0.00444
Haiku 4.5 $0.00007 $0.00222

Measured 2mo ago against content hash 2f6334f3e558, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

a2a-protocol 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 2mo 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.

.claude/skills/a2a-protocol/SKILL.md · 171 lines

How it starts

The opening of the file, as written. The whole thing — 171 lines — stays where its author put it; the contents beside it link to each section on GitHub.

A2A Protocol Reference

Reference skill for the Agent2Agent (A2A) Protocol, an open standard by Google / the A2A Project (Linux Foundation) for communication between independent AI agent systems.

Attribution: All specification and topic content in references/ is sourced from the official A2A repository under the Apache-2.0 license. Each file includes source attribution in its YAML frontmatter.

IMPORTANT — Use v0.3 by default. The primary references in references/v0.3/ are v0.3.0, the version currently supported by the official Go and Python SDKs and most implementations. The v1.0 RC spec is in references/v1.0-rc/ and should only be consulted when explicitly working on v1.0 features or migration planning.

When to use this skill

  • Building or debugging an A2A server or client
  • Configuring Ark A2AServer custom resources
  • Understanding Agent Cards, task lifecycle, or message formats
  • Implementing streaming (SSE) or push notifications
  • Working with A2A extensions
  • Comparing A2A with MCP

Protocol overview

A2A enables agents built on different frameworks to discover capabilities, negotiate interaction modes, manage collaborative tasks, and exchange information — without exposing internal state, memory, or tools.

Core actors:

  • User — human or automated service initiating a request
  • A2A Client — application or agent acting on behalf of the user
  • A2A Server — agent exposing an HTTP endpoint implementing A2A

Core elements:

Element Purpose
Agent Card JSON metadata: identity, capabilities, endpoint, auth
Task Stateful unit of work with unique ID and lifecycle
Message Single communication turn (role: "user" or "agent")
Part Content container: text, file reference, or structured data
Artifact Tangible output generated during a task

Read the full file on GitHub · 171 lines

Files

What ships with it

45 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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. 2mo ago First seen · 171 lines · 68 tokens per session scan A 2f6334f3e558

Subscribe to this mod's changes

a2a-protocol is a skill published in the GitHub repository mckinsey/agents-at-scale-ark (434 stars, last pushed yesterday), licensed Apache-2.0. It adds 68 tokens to every session and 2,219 once invoked, about $0.0003 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 2026-09-03.

Building agentsCloudDevOps and cloudagentic-aiaikubernetesproductid-20863
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a2a-protocol next to 6 skills from other repositories
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