a2a-bridge

a2a-bridge is a skill for Claude Code, Codex from vbcherepanov/a2abridge. It costs 76 tokens per session (1,083 once invoked), scanned A, original, MIT.

A system for sending messages and coordinating work between separate coding-agent sessions using the A2A protocol, a standard way for agents to communicate.

In plain words
What is it for?
Use it to notify another agent about a change, check an incoming inbox, find available agents, or coordinate work across projects.
Why use it?
It gives agents a shared way to discover peers, exchange updates, and track conversations as tasks.

Skill for Claude CodeCodex

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.

agentmods
npx agentmods add skills/vbcherepanov/a2abridge/skill
Any agent
npx skills add vbcherepanov/a2abridge --skill skill
Clone the repo
git clone --depth 1 https://github.com/vbcherepanov/a2abridge

Made for: Claude Code, Codex.

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-bridge

README.md
[![agentmods](https://agentmods.dev/badge/skills/vbcherepanov/a2abridge/skill.svg)](https://agentmods.dev/skills/vbcherepanov/a2abridge/skill)
Your own site
<a href="https://agentmods.dev/skills/vbcherepanov/a2abridge/skill"><img src="https://agentmods.dev/badge/skills/vbcherepanov/a2abridge/skill.svg" alt="Measured on agentmods" height="20"></a>
Per session 76 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,083 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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 $0.00076 $0.01083
Opus 5 $0.00038 $0.00541
Sonnet 5 $0.00015 $0.00217
Haiku 4.5 $0.00008 $0.00108

Measured 5d ago against content hash 58de219142f2, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

a2a-bridge 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 5d 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.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

internal/assets/skill/SKILL.md · 78 lines

How it starts

The opening of the file, as written. The whole thing — 78 lines — stays where its author put it; the contents beside it link to each section on GitHub.

a2a-bridge — inter-agent protocol skill

You are part of a distributed team of AI coding agents. Other Claude / Codex / Cursor sessions run in adjacent projects and you coordinate via the open A2A 1.0 protocol over a local discovery service. Your MCP host exposes the a2a_* tools; this skill teaches you when and how to use them.

Mental model

  • Each peer is identified by an Agent Card on /.well-known/agent-card.json and a unique URL.
  • Discovery is local: a2a_list_agents returns every peer registered with the directory.
  • Conversations are tasks: a2a_send_message creates a task on a peer; the peer replies via a2a_complete_task (or another a2a_send_message with the same task_id).
  • Your incoming queue is a2a_inbox. Hooks usually drain it for you before each prompt — but you should still call a2a_inbox(peek=true) once per turn as a safety net.

Self-label

You have a session-stable label of the form <basename-cwd>-<4hex> (e.g. a2abridge-3a2f). Prefix every outbound message text with [<label>] so peers can attribute it. Your inbox shows the sender's label the same way.

Inbound flow — every turn

Before answering the user, walk the inbox once:

  1. a2a_inbox(peek=true) — peek so the hook's drain remains authoritative.
  2. For each message decide:
    • FYI / context (breaking change in adjacent project, schema change, infra notice) → mention it in your reply to the user, then a2a_complete_task(text="acknowledged, will adjust on next pass").
    • Quick request answerable from current context (≤2 file reads) → answer immediately with a2a_complete_task(task_id=..., text=...).
    • Big request that would derail your current work → a2a_complete_task(text="queued, will pick up after <X>"), save the task id, continue with the user.
  3. Address the user's prompt last. If a peer's FYI changes what you should do, fold it into the response.

Outbound flow — proactive

Send a message to peers without being asked when your change is about to surprise them. Triggers:

Read the full file on GitHub · 78 lines

Files

What ships with it

1 file 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. 5d ago First seen · 78 lines · 76 tokens per session scan A 58de219142f2

Subscribe to this mod's changes

a2a-bridge is a skill published in the GitHub repository vbcherepanov/a2abridge (10 stars, last pushed 1mo ago), licensed MIT. It adds 76 tokens to every session and 1,083 once invoked, about $0.0004 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 2026-08-31.

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