agentmods.dev

mailbox

mailbox is a skill for Claude Code, Codex from zach-source/claude-mailbox. It costs 112 tokens per session (792 once invoked), scanned A, original, MIT.

A coordination guide for multiple Claude Code sessions working at the same time. It covers registering sessions, sending messages, discovering other workers, and choosing one leader for the main branch.

In plain words
What is it for?
Use it to coordinate agents across projects, branches, worktrees, or machines, including direct messages, requests, and handoffs.
Why use it?
It prevents concurrent sessions from duplicating work or making conflicting changes to the main branch.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: mentions Claude Code.

not rated 1repo 3mo ago A scan 112 tokens original MIT

Good fit Use it to coordinate agents across projects, branches, worktrees, or machines, including direct messages, requests, and handoffs.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/zach-source/claude-mailbox/mailbox
View source ↗ zach-source/claude-mailbox
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 zach-source/claude-mailbox --skill mailbox
Clone the repo
git clone --depth 1 https://github.com/zach-source/claude-mailbox

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 mailbox

README.md
[![agentmods](https://agentmods.dev/badge/skills/zach-source/claude-mailbox/mailbox/github.svg)](https://agentmods.dev/skills/zach-source/claude-mailbox/mailbox)
Your own site
<a href="https://agentmods.dev/skills/zach-source/claude-mailbox/mailbox"><img src="https://agentmods.dev/badge/skills/zach-source/claude-mailbox/mailbox/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 mailbox

Your own site · 80×15
<a href="https://agentmods.dev/skills/zach-source/claude-mailbox/mailbox"><img src="https://agentmods.dev/badge/skills/zach-source/claude-mailbox/mailbox.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 112 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 792 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 $0.00112 $0.00792
Opus 5.5 $0.00045 $0.00317
Sonnet 5.5 $0.00022 $0.00158
Haiku 4.5 $0.00011 $0.00079

Measured 2mo ago against content hash 8b00100ea0d7, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

mailbox 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.

skills/mailbox/SKILL.md · 60 lines

How it starts

The opening of the file, as written. The whole thing — 60 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Mailbox: cross-session coordination

Multiple Claude Code sessions run at once (different projects, branches, worktrees, machines). The mailbox MCP lets them see each other and cross-talk. State is backed by the shared beads_global database, so it works across projects and the fleet.

Push delivery (channels)

When the session is started as a channel (--dangerously-load-development-channels server:mailbox), peer messages arrive pushed as <channel source="mailbox" kind="dm|request|delegation|broadcast" from_sid="…" [request_id="…"]>…</channel> events — you don't have to poll. React to them: for kind="request" answer with respond_info passing the request_id; for kind="dm" reply with send_dm to the from_sid; for kind="broadcast" just take it into account. Without the channel flag, use poll_inbox / read_channel instead (same data, pull-based).

The one rule: a single leader on main

Exactly one session is the leader/orchestrator — the one on the main branch. Everyone else is secondary. register_session auto-claims leadership when you're on main; otherwise you're secondary and defer to the leader.

Protocol

  1. At session start — call register_session(objective="<one line of intent>"). Then list_sessions() and get_leader() so you know who's around and who leads before touching shared state.
  2. While working
    • update_objective(...) when your focus changes.
    • set_status("blocked") when stuck, "idle" when waiting, "done" when finished.
    • Glance at heartbeat() → inbox_count; if nonzero, poll_inbox().
  3. Before shared/destructive actions (editing main, flake.lock, deploys, migrations): if you're secondary, broadcast("<intent>", channel="<project>") first, or request_info/send_dm the relevant session. Don't stomp work in progress you can see in list_sessions().
  4. Answer promptly — if poll_inbox() shows a DM or the leader delegated work, respond. Another session may be waiting on you.
  5. On exit — set_status("done"); deregister() (the server also does this automatically at process exit).

Read the full file on GitHub · 60 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. 2mo ago First seen · 60 lines · 112 tokens per session scan A 8b00100ea0d7

Subscribe to this mod's changes

mailbox is a skill published in the GitHub repository zach-source/claude-mailbox (1 stars, last pushed 3mo ago), licensed MIT. It adds 112 tokens to every session and 792 once invoked, about $0.0004 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
Related

mailbox compared with skills from other repositories

mailbox next to 6 skills from other repositories
ModTypeStarsLast pushLicenceScanTokensWorks with
mailboxzach-source/claude-mailboxSkill13mo agoMITA112Claude Code, Codex
imagegenopenai/codexSkill135ktodayApache-2.0A113Codex
playwright-climicrosoft/playwrightSkill100ktodayApache-2.0A19Claude Code
browser-automationopenclaw/openclawSkill394ktodayMITA36Claude Code
local-ai-agentsmicrosoft/ai-agents-for-beginnersSkill79k4d agoMITA200Claude Code, Codex
systematic-debuggingobra/superpowersSkill316k7d agoMITA21Claude Code
next-cache-components-adoptionvercel/next.jsSkill143ktodayMITA95Claude Code