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swarmail: Mail between coding-agent sessions, on one machine or across machines

CI status Latest GitHub release Latest swarmail-mcp version on npm MIT license swarmail on Glama Swarmail MCP on MCPRush

MCP server · Threaded inbox and search · File reservations · Wake on mail

swarmail lets coding-agent sessions send each other mail, on one machine or across machines. Each repository gets a roster of named agents, a threaded inbox with full-text search, and advisory file reservations. Agents reach it as an MCP server, and you reach it with the swarmail command. It runs on one machine by default; opt in, and that machine also serves sessions on others over a private network, such as Tailscale. See Using it from another machine.

Find Swarmail on Glama and MCPRush.

It is one Bun binary with a SQLite database, listening on 127.0.0.1:18765. There are no runtime dependencies. Measured before the 0.2.0 release, a send took 0.46 ms and a search 0.65 ms at the median, it started in 38 ms and it idled at 32 MiB. See how it compares.

Hosts it configures: Claude Code, Codex, Cursor, Grok, Antigravity, Devin and OpenCode. Claude Code and Cursor sessions can also wake up when mail arrives. Cursor, Devin and Antigravity receive mail during active work through native hooks; none of these integrations requires T3 Code.

Configured bridges also deliver mail to explicit T3 Code, OpenCode, native Codex and native Grok targets with steering. They are opt-in foreground processes; installation does not start them. Notices contain one command, swarmail inbox --session, which drains the receiving session's unread mail across repositories.

Several hosts now message other sessions on their own. Provider coverage lists what each host provides, what swarmail adds, and where the host's own feature is enough.

Claude Code and Cursor sessions on one repository. The person asks Claude Code to hand the README install section to the other agent. Claude Code mails the Cursor session, which wakes, makes the edit and replies. Claude Code wakes on the reply and checks the change.

Recorded on 2026-10-03, with 0.2.0. Since 0.3.0 the wake notice reads "Swarmail: run swarmail inbox --session." instead of "Call fetch_inbox to read them."

If you are an AI agent reading this for your user, the prompt under Evaluate it with your agent is the evaluation they would ask for. Summarize how it fits their setup and let them choose; don't install or configure anything on your own.

Evaluate it with your agent

Paste this into a session with the agent you use. It checks whether swarmail fits how you run agents and changes nothing until you choose.

I'm considering Swarmail (https://github.com/bompus/swarmail), mail between
coding-agent sessions on one machine or across machines, served over MCP. Read its
README and docs/usage.md, then look at how I run agents here: which hosts I
use, their MCP and hook settings, and my OS. Tell me:
1. Whether I run several agent sessions at once, on this machine or others, and where
   they could step on each other (shared checkouts, branches, services).
2. Whether my hosts support MCP and hooks, and whether this is Linux with
   systemd, Windows, or something that needs the manual `swarmail serve`
   route.
3. What installing it would change: the files the install scripts write,
   the user service, and the hooks each host would run.
4. Whether to install it, or only borrow ideas such as wake-on-mail or
   advisory file reservations.
For rules that tell agents when to send mail, also look at house-rules
(https://github.com/bompus/house-rules) and its opt-in swarmail modifier.
Read only: don't install, configure or edit anything until I choose. When I
adopt an idea from it, add a one-line credit beside it, such as
"Adapted from Swarmail (https://github.com/bompus/swarmail)".

Taking individual ideas is welcome. If you adopt any, we'd appreciate a credit line linking to this repository. Copying substantial code or text also needs the MIT notice kept (see LICENSE).

Install

Requires Bun 1.4.2 or newer on Linux with systemd or on Windows 10 or 11. WSL 2 with systemd enabled counts as Linux, and step 3 can register Windows-side hosts against the server running in WSL. Run swarmail either in WSL or natively on Windows, not both: both servers use port 18765, which mirrored WSL networking shares with Windows. macOS is not supported yet.

Native Windows is a preview. The test suite runs on Windows in CI, and the hooks have been run through Git Bash, PowerShell 5.1, pwsh 7, cmd and Cursor's PowerShell form against a real server. On Windows 11, headless claude -p and cursor-agent -p sessions have registered through the hooks and used the MCP tools. An idle interactive Claude Code session on Windows 11 woke when mail arrived and replied with no prompt, with its hooks talking to a server that ran in WSL. Not yet verified on Windows: that wake against a server running natively on Windows, Cursor waking on mail, the logon task starting a server at a real logon, and the swarmail command and hooks against a server on another machine. If something fails there, please open an issue.

  1. Clone and install the dev tools:

    git clone https://github.com/bompus/swarmail.git
    cd swarmail
    bun install
  2. Build ~/.local/bin/swarmail and start the swarmail.service user unit:

    scripts/enable.sh

    On Windows, build ~\.local\bin\swarmail.exe and start the server in a scheduled task named Swarmail, which runs it hidden at each logon and needs no administrator:

    bun scripts/enable-windows.ts

    Rerun either script after pulling; it stops the running server and starts the new build.

    The database is ~/.local/share/swarmail/mail.sqlite3. The server has no authentication. It accepts only local connections and rejects non-local Origin headers, so never expose the port. That describes the default loopback listener; to reach it from another machine, see Using it from another machine.

  3. Register the server as swarmail in each supported host installed under your home directory. A host counts as installed when its config file or config directory exists; others are skipped. Add --dry-run to preview the edits:

    bun scripts/configure-mcp.ts

    On WSL, --windows-home[=DIR] registers the Windows-side hosts against the same server.

    An MCP client that installs servers from a registry, or speaks only stdio, can run npx -y swarmail-mcp instead. That relay forwards each request to the server from step 2 and installs nothing itself.

  4. Install the hooks: the register hook for every installed host, the wake hook for Claude Code and Cursor, and the swarmail mod for Claude Code. A host counts as installed when its config directory exists. Add --dry-run to preview the edits. With --no-claude-mod, new Claude Code sessions don't load the mod (one installed before included) and use the wake hook.

    bun scripts/configure-hooks.ts

    Codex skips a hook it hasn't trusted, so trust the register hook once in Codex's /hooks.

    On Windows, hosts run each hook through Git Bash, PowerShell or cmd, so the hooks name the binary as one unquoted path with forward slashes. If your profile path has a space or a non-ASCII letter, the hooks use its 8.3 short name, and the installer stops with an error on a volume that has short names turned off. Cursor passes hook input through Windows PowerShell 5.1, which turns non-ASCII characters into ?, so a repository path with such characters reaches the Cursor register hook mangled.

  5. Optional: bun scripts/install-guard.ts [repo...] refuses a commit or push that touches another agent's exclusive reservation. It installs into hooks.d/pre-commit/ and hooks.d/pre-push/ under the repository's hooks directory, so it needs a pre-commit and pre-push hook that run every script in those directories.

Start a new agent session and edit a file in a repository. The register hook gives the session a name such as BlueLake. Run swarmail who in that repository to see it.

How agents use it

Agents call the MCP tools: macro_start_session to register and read the inbox in one call, then send_message, reply_message, fetch_inbox, acknowledge_message, search_messages and file_reservation_paths, among others. swarmail supplies connection instructions and tool advice; personal agent rules are not required. swarmail --help shows the same briefing. docs/usage.md explains the details and client refresh limits.

Each repository is one project, keyed by its primary checkout. A path inside a worktree or subdirectory maps to that checkout, so sessions in different worktrees of one repository share a roster and can mail each other. A session keeps one name across repositories.

Commands

Command What it does
swarmail serve Run the server
swarmail who [repo] Agent names, session titles and edit checkouts, live sessions first
swarmail inbox, send, search Read, send or search mail as this session
swarmail thread <id> One thread's messages, oldest first
swarmail inbox --session Drain this session's unread mail across repositories
swarmail wake-bridge <config.json> Deliver notices to one explicitly configured local target
swarmail send <to> <subject> <body> --notification-policy quiet Store normal/low informational mail without an automatic inbox hint
swarmail ping <agent> Exit 0 if that agent's wake hook is waiting
swarmail register The register hook; --tag prints the tag for a manual registration; --host <host> selects the host explicitly
swarmail hook wake <host> The Claude Code and Cursor wake hook
swarmail hook context <cursor|devin|agy> [stop] Check mail at a native context point without cancelling the task
swarmail hook rearm The Claude Code re-arm on Windows, which has no POSIX shell to run the Linux one
swarmail guard The git guard
swarmail version The source hash the binary was built from
swarmail updates --session Approved update targets and loaded-revision confirmations
swarmail overdue [--dry-run] Remind recipients of unacknowledged ack_required mail; report to the operator (setup)
swarmail wake-auto-t3 <config.json> [--check | --retry-thread <id>] Experimental, Linux only: wakes T3 Codex and Orchestrator V2 Cursor sessions (setup)
swarmail canary One send, wake and acknowledge round trip, logged for a timer (setup)
swarmail pr-sessions <PR URL> --project <checkout> T3 conversations and agents linked to a pull request (details)

swarmail --help lists every subcommand and flag. A --help or -h anywhere prints usage and runs nothing.

Settings

Variable Default Effect
SWARMAIL_DB ~/.local/share/swarmail/mail.sqlite3 Database path
SWARMAIL_PORT 18765 Server port
SWARMAIL_HOST unset Also listen on this one non-loopback address, such as a Tailscale IP; needs SWARMAIL_TOKEN_FILE
SWARMAIL_TOKEN_FILE unset A file whose first line is a bearer token of 32 or more characters. The server requires it on SWARMAIL_HOST; the command, the register hook and the relay send it
SWARMAIL_URL http://127.0.0.1:18765/mcp/ MCP endpoint for the command, the register hook and the swarmail-mcp relay
SWARMAIL_WAKE_URL http://127.0.0.1:18765 Server base URL for the wake hook
SWARMAIL_SYNCHRONOUS normal full syncs every commit, at about 3 ms per send instead of 0.5 ms
SWARMAIL_ENABLE_MUTATIONS 0 Enable sender withdrawal/priority edits only after all readers are qualified; rollout and rollback requirements
SWARMAIL_RETIRE_DAYS 7 Retire idle agents and drop projects whose checkout is gone; 0 keeps both
SWARMAIL_GUARD block warn only reports, off skips
SWARMAIL_AGENT from hook state Name used by inbox, send, ping, guard and who
SWARMAIL_LIVE_ROOM unset A JSON heartbeat file (heartbeatAt, plus agentName, hostSessionId or t3Thread); while its heartbeat is under 5 minutes old, who flags the session it names
SWARMAIL_UPDATE_TARGETS unset Absolute approved-target manifest; quiet session checks and loaded-revision confirmations
SWARMAIL_UPDATE_HOLD unset 1 holds update hints and confirmations for a frozen session context

scripts/enable.sh, scripts/enable-windows.ts, the service unit and configure-mcp.ts use port 18765. Change SWARMAIL_PORT and the two URL variables only when you run swarmail serve yourself, and set them for every host that runs the hooks. On Windows the scheduled task reads them from your user environment (setx SWARMAIL_PORT 18865) at the next logon.

Using it from another machine

By default the server listens on 127.0.0.1 only. To let sessions on another machine use it, make one machine the hub and give it a second listener on a private-network address. Create the token, then set the two variables for the server you already run and restart it:

umask 077 && head -c 32 /dev/urandom | base64 | tr -d '\n=+/' > ~/.config/swarmail-token
systemctl --user edit swarmail   # under [Service]: Environment=SWARMAIL_HOST=<tailscale ip -4>
                                 #                   Environment=SWARMAIL_TOKEN_FILE=%h/.config/swarmail-token
systemctl --user restart swarmail

On Windows set the two variables in your user environment and sign in again. A second swarmail serve started by hand fails while the installed one holds 127.0.0.1:18765, so stop the service first if you run it that way.

The loopback listener is unchanged, so local hosts and hooks keep working without a token, and the command and register hook send the token only to a URL that is not loopback. The server accepts any one non-loopback address, public ones included, so name a private-network address; a client with the token can read the roster, project paths and reservations as well as mail. The extra listener speaks plain HTTP, so the token and the mail are unencrypted on the wire: use a network that encrypts and authenticates every peer, such as Tailscale, and never an ordinary shared or public network. The extra listener answers every route except /healthz only with Authorization: Bearer <token>, and the server refuses to start with SWARMAIL_HOST set to a loopback or wildcard address or without a token file. Copy the token file to the other machine, then point its swarmail command, register hook and relay at the hub:

SWARMAIL_URL=http://<hub address>:18765/mcp/ SWARMAIL_TOKEN_FILE=~/.config/swarmail-token swarmail who

A host that connects to MCP over HTTP itself needs the same Authorization header in its server entry, or swarmail-mcp as a relay.

Against a remote server a project is named by the repository, not by a path: the URL git uses for the clone's origin remote, written git:host/owner/repo in lower case whatever the protocol (https://github.com/bompus/swarmail.git and git@github.com:bompus/swarmail.git are the same repository). Only the host and path count: the user, port, .git suffix and a leading slash are ignored, and a url.<base>.insteadOf rewrite is applied first. When the hub holds a clone of that repository, its project is the remote sessions' project too, so both machines share one roster, mail and set of reservations. If the hub meets the clone later, its project takes over the one the remote sessions created. A hub that holds several clones of the repository uses the one registered first, and a hub clone that registered before it had an origin keeps its own project, apart from the one remote sessions created for the repository. A clone with no origin remote cannot be named to a remote server; the command says so, and the hook says so when the session starts. A clone whose origin git cannot read keeps the project it had. The hook does not take a name that another session holds in the project, and the server refuses to give a retired session's name to a different session; the hook then takes a fresh name. Two sessions that carry the same name into a repository's project at the same moment can still collide, because the hook reads the roster before it registers.

Checked so far: on 2026-10-26 a Windows 11 PC reached a Linux hub over Tailscale and passed ten checks: the token is required, a session registers by repository name and shares the hub clone's project, mail goes both ways, a reply wakes a waiting session, and the roster shows it waiting and then ended. That run called the server's HTTP interface from a script. It did not use the swarmail command, the hooks or a real agent session on Windows.

Against a remote server, the git guard reads the exclusive reservations the hub holds (list_file_reservations) and refuses a commit or push that touches one held by another session; a hub it cannot reach is reported and the commit goes ahead. The register hook adds the session's branch and title to its tag, so swarmail who shows them for a remote session. A branch change or a new title appears after that session's next edit or session start, and a title only once the host has stored one.

What does not carry over yet:

  • swarmail who shows a remote session as alive ("waiting for mail on the server") only while a wake hook or bridge of that session has a wait that began after its last end report, and as ended after the session's SessionEnd hook reports it, until the session acts again (sends, reserves, reads its inbox, changes its mail) or waits again. A session that is mid-turn, or has no wake hook, shows as liveness unknown. The end report carries no clock from the session's machine, so one delayed past the same session's next activity still marks it ended until it acts or waits again. A session registered in several projects reports its end in each, and acting in one project does not clear the report in another. Presence is keyed by the provider's session ID and the T3 thread, not by project or host: an end report from an earlier registration that shares its session ID with a successor in another T3 thread (or its T3 thread with a successor in another project) can mark the successor ended, or hide its open wait, until the successor acts or waits again. A registration with only a provider session ID, linked to a T3 thread by another project's registration, does not see that thread's waits. Waits are counted by the server process that holds them, so a second server on the same database does not see the first one's waits. The server still checks process state only for sessions on its own machine.
  • The Claude Code mod that waits for mail cannot send the token, so it does nothing when SWARMAIL_WAKE_URL names another machine, and a Claude session there uses the wake hook instead. Wake hooks and bridges send the token to a remote SWARMAIL_WAKE_URL or swarmailUrl.
  • swarmail overdue refuses to run against a remote server, because it reads this machine's records; run it on the hub.
  • A session belongs to the one server it registered with. If its hooks later reach a different server, they leave it unregistered there and say to start a new session, and swarmail inbox, send and the git guard do not use its name at the other server.
  • swarmail who shows no unread counts for a remote server, because it counts them in this machine's database, and it takes a path inside the checkout, not a project name, because it cannot list the server's projects.
  • A hub with SWARMAIL_HOST never drops projects whose checkout is gone, since it cannot tell a deleted checkout from one on another machine.
  • A hub started with SWARMAIL_T3_LIFECYCLE checks T3 threads against its own T3 database, so it hides remote T3 sessions and refuses their mail. Leave it unset on a hub that serves remote T3 sessions.

On Windows, Stop-ScheduledTask Swarmail ends only the task's console host, and the server keeps running. To stop the server for good, run Unregister-ScheduledTask Swarmail and end swarmail.exe in Task Manager.

With normal, a power loss can lose the most recent writes. A retired agent comes back when it registers again or sends, reads mail or reserves files as itself.

Maintenance and retention

The server runs cleanup at startup and hourly. With SWARMAIL_RETIRE_DAYS above zero, it retires agents inactive longer than that many days. It also removes gone projects with no mail, active reservations or agent activity in the last day. Paths outside the user home are not judged gone.

Setting SWARMAIL_RETIRE_DAYS=0 preserves those agents and projects; it does not disable retry-key cleanup. Keys older than seven days are removed at startup and hourly regardless of this setting. A retry replays until its key is removed; afterward, it may perform the operation again. These sweeps do not delete message bodies. Account for expired retry keys before a server restart; retaining the database file alone does not guarantee every row survives startup.

Read-only MCP requests do not suspend cleanup. A client that starts a server instance triggers its startup sweep; an existing server can sweep hourly while qualification runs. Check expired retry keys before preservation-sensitive qualification. A row disappearing during a read-only check alone does not identify which process or sweep removed it.

Register hook

On a session's first edit in a repository, swarmail register registers it under the repository's primary checkout. Claude Code and Cursor also run it when a session starts. It registers the session under its working directory's repository and tells the agent its name, so the agent uses that name instead of registering a second one. Where another session already holds that name in the project, the hook registers the session there under a different name and says so. A claude -p run whose CLAUDE_CODE_ENTRYPOINT is sdk-cli registers on its first edit instead, so a read-only one-shot run adds no agent. A child that inherited sdk-ts from an SDK-hosted session still registers at start. The registration starts with a tag holding the host's session id and working directory, which is how swarmail who matches names to sessions. A failure is retried on the next prompt or edit; a retry for an edit checkout that has since been deleted is dropped. State lives in ~/.local/state/swarmail-register/, under your profile on Windows. After upgrading, run bun scripts/configure-hooks.ts again to add the session-start hook.

Host Session id in the shell
Claude Code $CLAUDE_CODE_SESSION_ID
Codex $CODEX_THREAD_ID
Cursor $CURSOR_CONVERSATION_ID
OpenCode, Devin none; their hooks carry it

Waking sessions

Claude Code sessions wake through the swarmail mod (src/claude-wake-mod.js), which waits for mail for as long as the session runs. The installer copies it to ~/.local/share/swarmail/claude-plugin and adds that directory to env.CLAUDE_CODE_PLUGIN_DIRS in ~/.claude/settings.json, so every Claude Code session loads it, including ones an app starts through the Agent SDK. When mail arrives at an idle session, the mod starts a turn with a one-line short instruction to read the session inbox. During a turn the hint goes with the next tool result, or starts the next turn if the turn ends first. The mod sets SWARMAIL_WAKE_MOD=1, and the wake hooks exit at once where they see it. It was tested with Claude Code 2.1.288. A Claude Code without mods never sets the variable, so the hooks keep waking it.

Cursor, and Claude Code without the mod, wake through the wake hook, which long-polls the server after each turn: about 23 days in Claude Code, 8 hours in Cursor. When mail arrives, it starts a new turn with the hint. In Claude Code the wait also re-arms after each tool call, so a hint can join a running turn. Cursor stops continuing on its own after five wakes with no prompt from a person, so further mail waits for the next prompt (tested). The server answers swarmail ping itself, so a ping never wakes the model. Hosts without a wake integration see mail on their next fetch_inbox.

Native Cursor uses postToolUse additional context; Devin uses PostToolUse additional context and its own user configuration. Antigravity uses a PreInvocation user message. Checks are bounded and use GET /wait?session=<id>&timeout=0, which returns immediately and keeps the wake cursor's delivery suppression. Message bodies and read/ack receipts stay in swarmail. Devin and Antigravity can continue at Stop when new mail is already present; their synchronous hooks cannot wait indefinitely for mail arriving after the session has stopped. These hooks add information; the receiver decides whether its current task needs to pause.

Quiet mail remains available through inbox and search. Automatic wake paths and mailbox snapshots exclude it; see notification policy.

Adapters can revalidate a queued hint with GET /wait/peek?session=<id>. It returns { "mailboxes": [{ "recipient": "GreenCastle", "project": "/w/project" }] } for the session's wake-eligible unread mail, including mail already offered. High and urgent mailboxes come first. This request leaves waiters, wake cursors, read receipts and pings unchanged. Unknown or retired sessions return an empty list. More than 1000 mailboxes returns HTTP 503 instead of a partial snapshot.

Feature comparison

These are the six servers measured below. Features describe the pinned source versions in the detailed comparison, which also covers runtimes, platforms, licences and two additional servers.

Server Roster scope Search Threads and receipts File reservations Wakes an idle session
Swarmail Per repository; worktrees share it Full text (FTS5) Threads; read, acknowledged and delivery receipts Advisory, with a git guard Claude Code and Cursor
mcp_agent_mail_rust Per project path Full text (Tantivy) Threads; read, acknowledged and delivery receipts Advisory, with a git guard No; Claude Code hooks check the inbox during a turn
mcp_agent_mail Per project path Full text (FTS5) Threads; read and acknowledged Advisory, with a git guard that is off by default No; Claude Code, Codex and Factory hooks check the inbox during a turn
agent-inbox One per hub Substring, at most 25 results Threads; read state None Claude Code (opt-in hook), opencode, omp
agentbus One per server None No threads; reading moves a cursor None No; an agent waits in recv for up to 600 s
Project Relay Per project None Replies; acknowledged per recipient Advisory leases No; an inbox read waits for up to 25 s

An inbox read that waits for mail needs an agent already running. It does not wake an idle session.

Performance

Measured on 2026-10-04 at 67e187a. These results come from a commit six commits before the 0.2.0 tag and have not been remeasured for 0.2.0 or any later release. The measurements used one machine with one small workload (40 agents, 250 seed messages, 1,560 messages by the end). Each server started on empty storage. Startup is hyperfine's mean of 20 runs; every other number is the median of three rounds, with latency from Tinybench and requests per second from oha. docs/benchmarks.md has the method, a sixth server, each tool's raw output and a feature comparison with seven other local agent-mail servers.

Bar charts sorted from best to worst for each metric. Send p50: Swarmail 0.46 ms, agentbus 2.3 ms, Project Relay 2.5 ms, Rust Agent Mail 39 ms, Python Agent Mail 70 ms. Search p50: Swarmail 0.65 ms, Python Agent Mail 12 ms, Rust Agent Mail 56 ms; agentbus and Project Relay have no search tool. Startup: Swarmail 38 ms, Project Relay 123 ms, agentbus 408 ms, Python Agent Mail 0.86 s, Rust Agent Mail 1.5 s. Idle memory: Swarmail 32 MiB, agentbus 81 MiB, Project Relay 121 MiB, Python Agent Mail 154 MiB, Rust Agent Mail 190 MiB.

Each chart ranks its metric from best to worst. Lower values are better in all four charts. The tables below put servers in rows and units in headings. Rust Agent Mail and Python Agent Mail are mcp_agent_mail_rust and mcp_agent_mail.

Latency

Median latency in milliseconds; lower is better. Rows are sorted by send latency. Search has a different ranking. A dash means no search tool.

Server Send ↓ Inbox ↓ Search ↓
Swarmail 0.46 0.50 0.65
agentbus 2.3 1.1 —
Project Relay 2.5 1.4 —
Rust Agent Mail 39 12 56
Python Agent Mail 70 23 12

Throughput

Requests per second with eight clients; higher is better. Rows are sorted by send throughput. Search has a different ranking.

Server Send ↑ Inbox ↑ Search ↑
Swarmail 5,500 6,300 4,300
agentbus 876 1,600 —
Project Relay 482 1,100 —
Rust Agent Mail 50 416 90
Python Agent Mail 9.7 27 44

Memory

Resident memory in MiB; lower is better. Rows are sorted by idle memory. Peak memory has a different ranking.

Server Idle ↓ Peak under load ↓
Swarmail 32 67
agentbus 81 96
Project Relay 121 296
Python Agent Mail 154 258
Rust Agent Mail 190 688

CPU usage, seed-loading times and the full ratios are in the detailed results.

Startup

Mean startup time in milliseconds across 20 hyperfine runs; lower is better. Rows are sorted by mean time. Each run starts the server, waits for its health check, then stops it.

Server Mean ± SD ↓ Min Max
Swarmail 37.7 ± 0.7 37.1 39.3
Project Relay 122.9 ± 5.3 113.8 132.7
agent-inbox* 263.0 ± 11.4 252.0 297.9
agentbus 408.2 ± 15.6 385.1 443.3
Python Agent Mail 857.7 ± 38.7 803.5 925.7
Rust Agent Mail 1530.3 ± 14.9 1509.6 1562.8

The harness without a server takes 7.2 ± 0.6 ms (min 6.6, max 8.5). Hyperfine's raw Relative column compares against that harness, not swarmail; see the startup output.

* agent-inbox appears only in startup here. Its inbox pages hold 50 messages instead of 20, its roster is global and its search matches substrings, so its fetch, list and search do different work. The detailed comparison has its full column.

mcp_agent_mail commits each send to a Git archive before it returns, so these numbers don't compare durability. Requests per second varied by up to 29% between rounds of the same server.

Development

Bun's formatter checks authored Markdown, HTML, JSON, JSONC, YAML, TOML and CSS as well as JavaScript and TypeScript. The generated dependency lockfile stays excluded. Package fields and dependency maps are sorted; script order is preserved.

Archived validator research records the generated/runtime comparison, TypeBox compatibility findings and the limits of the measurements for the tested mail contracts.

bun install
bun test
bun run check   # format, lint and type check

bun run check checks formatting with Bun's bun fmt and type-checks with bun check, which need Bun 1.4.4 or later.

bun scripts/build.ts --if-stale rebuilds the binary only when a source file, the dependency manifest or lockfile, the bytecode-order profile, the build script, or the Bun version changed. Restart the unit to load a new build.

The build passes scripts/swarmail.order to Bun's --bytecode-order (Bun 1.4.3 or later; earlier versions ignore it). After a change to what the server runs at start-up or in its common calls, record the profile again with bun scripts/train-bytecode-order.ts and commit the new file. A profile from older sources still applies, because Bun matches functions by a hash of their syntax.

Sponsoring

swarmail is built and maintained by one person. If it saves you time, you can sponsor it monthly or once through GitHub Sponsors, or leave a tip on Ko-fi.

Licence

MIT. CODE_OF_CONDUCT.md is the Contributor Covenant under CC BY 4.0; see THIRD_PARTY_NOTICES.md. To contribute, see CONTRIBUTING.md.

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Mail between coding-agent sessions, on one machine or across machines: an MCP server and CLI on Bun and SQLite.

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