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

Use it to notify another agent about a change, check an incoming inbox, find available agents, or coordinate work across projects.

It gives agents a shared way to discover peers, exchange updates, and track conversations as tasks.

a2a-bridge — Skill for Claude Code by vbcherepanov/a2abridge

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 vbcherepanov/a2abridge --skill skill

Clone the repo

git clone --depth 1 https://github.com/vbcherepanov/a2abridge

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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/vbcherepanov/a2abridge/skill/github.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/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.

Your own site · 80×15

<a href="https://agentmods.dev/skills/vbcherepanov/a2abridge/skill"><img src="https://agentmods.dev/badge/skills/vbcherepanov/a2abridge/skill.svg" alt="Reviewed on agentmods" width="80" 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 1,135 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.

Model	Per session	Once invoked
Fable 5.1	$0.00076	$0.01135
Opus 5.5	$0.00030	$0.00454
Sonnet 5.5	$0.00015	$0.00227
Haiku 4.5	$0.00008	$0.00113

Measured 1mo ago against content hash a4d13fb174ec, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, 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 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.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

a2a-bridge — 100% identical, 0 lines differ

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.
Every message is its own task: a2a_send_message creates a task on the peer, which stays working until the peer answers with a2a_complete_task. Continue a conversation with a new message that reuses the context_id of the previous task. Pass task_id only for a task that is waiting for input — A2A 1.0 rejects messages to a task that is still being worked on or already finished.
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:

a2a_inbox(peek=true) — peek so the hook's drain remains authoritative.
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.
Address the user's prompt last. If a peer's FYI changes what you should do, fold it into the response.

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.

references/protocol.md 4.1 KB

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.

1mo ago Changed a4d13fb174ec
2mo 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 (16 stars, last pushed 6d ago), licensed MIT. It adds 76 tokens to every session and 1,135 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 2026-08-31.

Building agents Claude Code a2a ai-agents cline codex-cli cursor

a2a-bridge next to 6 skills from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
a2a-bridgevbcherepanov/a2abridge	Skill	16	6d ago	MIT	A	76	Claude Code
telegram-agentbeautyfree/telegram-agent	Skill	11	1mo ago	GPL-3.0	A	90	Claude Code, Codex
verifyyha9806/academic-writing-toolkit	Skill	54	11d ago	MIT	A	26	Claude Code
ainb-fleet:daemonstevengonsalvez/agents-in-a-box	Skill	27	9d ago	MIT	A	89	Claude Code
ainb-fleet:broadcaststevengonsalvez/agents-in-a-box	Skill	27	9d ago	MIT	A	114	Claude Code
calibration-technicianwonsukchoi/domain-experts	Skill	25	5d ago	MIT	A	112	Claude Code, Codex
aerospace-engineering-technicianwonsukchoi/domain-experts	Skill	25	5d ago	MIT	A	169	Claude Code, Codex