swimmers

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cargo install swimmers
swimmers-tui        # opens the aquarium — no server process to manage

A terminal aquarium for your tmux sessions. Each session becomes an animated fish whose behavior reflects its real-time state — swimming when active, bubbling when busy, dozing when idle. Backed by a Rust API server that discovers and manages tmux sessions, with a native TUI client that renders the whole thing as a fish bowl you can navigate, inspect, and control.

TL;DR

The Problem: You have a dozen tmux sessions running across a machine. Listing them with tmux ls gives you cryptic one-liners. You can't tell at a glance which sessions are busy, which are idle, which need attention, and which have errored out. Switching between them is a context-destroying exercise in remembering session names.

The Solution: Swimmers turns your tmux sessions into a visual fish bowl. Each session is an animated ASCII fish. Active sessions swim, busy ones blow bubbles, sleeping ones sink to the bottom, errored ones show x eyes. Select a fish to inspect its pane output, open it in your desktop terminal, or read the thought stream from your AI coding agents.

Why swimmers?

Installation

From crates.io

cargo install swimmers

That installs two binaries on your PATH:

• swimmers-tui — the aquarium TUI. By default it hosts the API in-process, so one command is enough to get started.
• swimmers — the standalone Axum HTTP/WebSocket API server. Use it when you want a long-running headless server, multiple TUI clients against one backend, or remote access over Tailscale. Run it as swimmers or, equivalently, swimmers serve.

No repo checkout required.

Prerequisites

From Source

git clone https://github.com/build000r/swimmers.git
cd swimmers
cargo build --release

Binaries land in target/release/swimmers (API server) and target/release/swimmers-tui (TUI client). You can also run cargo install --path . from inside the checkout.

Quick Start

After cargo install swimmers, both swimmers and swimmers-tui are on your PATH. No clone required.

1. Open the TUI

   swimmers-tui
   

   The TUI hosts the API in-process by default — no separate server to start, no port to worry about, no handshake message while you wait for something to boot. Quit with q and the whole thing exits cleanly.

2. Create some tmux sessions if you don't have any yet

   tmux new-session -d -s dev
   tmux new-session -d -s logs
   tmux new-session -d -s deploy
   

   They appear in the aquarium within seconds.

3. Navigate — arrow keys to select a fish, Enter to open the session in your terminal, q to quit the TUI.

External server mode

Set SWIMMERS_TUI_URL to run the API as a separate process (for multi-client access, remote access over Tailscale, or integration with the REST endpoints from curl/browser). The TUI switches to HTTP transport and, for loopback URLs, auto-spawns a sibling swimmers binary if one isn't already listening — using a readiness pipe instead of polling, so the handoff is invisible.

SWIMMERS_TUI_URL=http://127.0.0.1:3210 swimmers-tui

To run the API explicitly as a standalone headless server:

swimmers          # same as `swimmers serve`
# or
swimmers serve    # explicit form for service managers and docs

Ctrl-C stops it. kill $(lsof -ti:3210) works for a backgrounded instance.

Bind Address and Network Access

Bind addresses only apply to the standalone swimmers / swimmers serve binary. Embedded mode (swimmers-tui with no SWIMMERS_TUI_URL) binds no socket at all.

By default the server binds to 127.0.0.1:3210 (loopback only).

Loopback (default, no auth required)

swimmers                                            # binds 127.0.0.1:3210
SWIMMERS_TUI_URL=http://127.0.0.1:3210 swimmers-tui # opt into external HTTP transport

External / Tailscale access

Set SWIMMERS_BIND to expose the server on a non-loopback interface. The server refuses to start if you pair a non-loopback bind with AUTH_MODE=local_trust; for external exposure, switch to AUTH_MODE=token and set AUTH_TOKEN.

# Bind to all interfaces (e.g., for Tailscale access from another machine)
SWIMMERS_BIND=0.0.0.0 \
AUTH_MODE=token \
AUTH_TOKEN=your-secret-token \
swimmers

# Bind to a specific Tailscale IP
SWIMMERS_BIND=100.101.123.63 \
AUTH_MODE=token \
AUTH_TOKEN=your-secret-token \
swimmers

# Point the TUI at the remote server
SWIMMERS_TUI_URL=http://100.101.123.63:3210 \
AUTH_MODE=token \
AUTH_TOKEN=your-secret-token \
swimmers-tui

For any non-loopback bind, use AUTH_MODE=token with AUTH_TOKEN. OBSERVER_TOKEN is optional when you also want a read-only credential for browser or observer clients.

Environment Variables

When SWIMMERS_NATIVE_APP=ghostty, the API uses Ghostty's AppleScript support to create or replace a left-side preview split for the selected tmux session. This path requires Ghostty 1.3.0+ on macOS with automation access enabled.

While the TUI is running, press n or click the top-right native-open label to switch between iTerm and Ghostty without restarting the API.

The optional browser terminal renderer also honors SWIMMERS_FRANKENTUI_PKG_DIR (or FRANKENTUI_PKG_DIR) to override the auto-detected frankentui/pkg asset path.

Make Targets

If you are working from a source checkout, the Makefile has convenience targets:

make tui                # Launch swimmers-tui (embedded mode by default)
make web                # Start the standalone server and print local browser URLs
make server             # Run only the standalone API server
make tui-check          # Wait for an existing API (external mode only), then exit
make tui-smoke          # Run shell-level bootstrap tests on the run-tui.sh shim
make cargo-cov-lcov     # Generate lcov coverage report

Configuration

Swimmers reads all configuration from environment variables. There is no config file. Defaults are sane for local use:

# Minimal local usage (everything defaults)
swimmers

# External access with token auth
SWIMMERS_BIND=0.0.0.0 \
AUTH_MODE=token \
AUTH_TOKEN=your-secret-token \
swimmers

Repo Themes

Drop a .swimmers/colors.json in any repo directory to override session colors and the repo's default sprite. The TUI discovers themes automatically, and the header [auto] sprite mode uses the repo default before falling back to the built-in default.

{
  "sprite": "jelly",
  "palette": {
    "body": "#B89875",
    "outline": "#3D2F24",
    "accent": "#1D1914",
    "shirt": "#AA9370"
  }
}

Valid sprite values are fish, balls, and jelly. The header sprite toggle can still force a global override for the current TUI session.

Architecture

Default: embedded mode

swimmers-tui hosts the API in the same process. No port, no handshake, no second binary. All the subsystems below run in one Tokio runtime alongside the render loop.

┌──────────────────────────────────────────────────────────────┐
│                         swimmers-tui                         │
│  Aquarium view  |  Thought rail  |  Mermaid viewer           │
│  Keyboard/mouse navigation  |  Native terminal handoff       │
│──────────────────────────────────────────────────────────────│
│  InProcessApi (TuiApi trait) — zero HTTP, zero JSON          │
│──────────────────────────────────────────────────────────────│
│  SessionSupervisor, SessionActor, Thought subsystem,         │
│  FileStore — the same subsystems the standalone server       │
│  runs, just in the same process.                             │
└───────────────────────────┬──────────────────────────────────┘
                            │ PTY / shell exec
                            ▼
┌──────────────────────────────────────────────────────────────┐
│                         tmux server                          │
└──────────────────────────────────────────────────────────────┘

External mode (SWIMMERS_TUI_URL)

Set SWIMMERS_TUI_URL to split the API into its own process. Multiple TUIs, headless setups, remote access, and direct REST/curl use all take this path. For loopback URLs the TUI auto-spawns a sibling swimmers binary using a readiness-pipe handshake (no curl polling).

┌──────────────────────────────────────────────────────────────┐
│                     swimmers-tui (client)                     │
│  Aquarium view  |  Thought rail  |  Mermaid viewer           │
│  Keyboard/mouse navigation  |  Native terminal handoff       │
└───────────────────────────┬──────────────────────────────────┘
                            │ HTTP (REST JSON)
                            │ auto-spawns `swimmers` for loopback
                            │ URLs via readiness-pipe handshake
                            ▼
┌──────────────────────────────────────────────────────────────┐
│            swimmers  (a.k.a. `swimmers serve`)                │
│  Axum router  |  Auth middleware  |  Prometheus /metrics      │
├──────────────────────────────────────────────────────────────┤
│  SessionSupervisor                                           │
│    ├─ tmux discovery loop                                    │
│    ├─ lifecycle broadcasts                                   │
│    └─ persistence checkpoints                                │
│  SessionActor (per session)                                  │
│    ├─ PTY I/O via portable-pty                               │
│    ├─ replay ring buffer                                     │
│    ├─ state detection (idle/busy/error/attention)             │
│    └─ ScrollGuard (redraw burst coalescing)                  │
│  Thought subsystem                                           │
│    ├─ bridge runner (daemon mode)                             │
│    └─ loop runner (in-process mode)                           │
├──────────────────────────────────────────────────────────────┤
│  FileStore (data/swimmers/)  — flat-file persistence         │
└───────────────────────────┬──────────────────────────────────┘
                            │ PTY / shell exec
                            ▼
┌──────────────────────────────────────────────────────────────┐
│                         tmux server                          │
│  Sessions  |  Windows  |  Panes                              │
└──────────────────────────────────────────────────────────────┘

API Endpoints

Running in Background

nohup

nohup swimmers > swimmers.log 2>&1 &

systemd (Linux)

sudo tee /etc/systemd/system/swimmers.service << 'EOF'
[Unit]
Description=Swimmers Terminal Manager
After=network.target

[Service]
Type=simple
User=your-username
Environment=SWIMMERS_BIND=127.0.0.1
Environment=PORT=3210
ExecStart=/home/your-username/.cargo/bin/swimmers
Restart=on-failure
RestartSec=5

[Install]
WantedBy=multi-user.target
EOF

sudo systemctl daemon-reload
sudo systemctl enable --now swimmers

macOS LaunchAgent

mkdir -p ~/Library/LaunchAgents

cat > ~/Library/LaunchAgents/com.swimmers.plist << 'EOF'
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN"
  "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>com.swimmers</string>
    <key>ProgramArguments</key>
    <array>
        <string>/Users/your-username/.cargo/bin/swimmers</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
    <key>KeepAlive</key>
    <true/>
    <key>StandardOutPath</key>
    <string>/tmp/swimmers.log</string>
    <key>StandardErrorPath</key>
    <string>/tmp/swimmers.err</string>
</dict>
</plist>
EOF

launchctl load ~/Library/LaunchAgents/com.swimmers.plist

How swimmers Compares

When to use swimmers:

• You run many tmux sessions and want a visual overview
• You use AI coding agents and want to see their thought streams
• You want to monitor remote sessions from a local TUI

When swimmers is not the right tool:

• You only use one or two tmux sessions (tmux is fine on its own)
• You need a tmux session template/layout manager (use tmuxinator)

Troubleshooting

TUI cannot reach the API

This only applies to external mode (SWIMMERS_TUI_URL set). Embedded mode (the default) does not talk to a network at all.

# Check if the API is running
curl -s http://127.0.0.1:3210/v1/sessions

# Start it
swimmers          # or: swimmers serve

If you want to avoid the external-mode setup entirely, unset SWIMMERS_TUI_URL and run swimmers-tui directly — it hosts the API in-process.

TUI gets 401 or 403

The API is running with token auth. Set your credentials:

AUTH_MODE=token AUTH_TOKEN=your-token swimmers-tui

No sessions showing in the aquarium

Create at least one tmux session:

tmux new-session -d -s dev

Port already in use

lsof -ti:3210 | xargs kill
swimmers

Cargo build fails

rustup update stable
cargo clean
cargo build --release

Limitations

• tmux only — swimmers does not manage screen, zellij, or plain terminal sessions
• Browser UI is terminal-first — the web surface is for remote attach/control; the animated aquarium remains native-only
• Single-machine sessions — the API manages tmux sessions on the machine it runs on; it does not aggregate sessions across multiple hosts
• No session templating — swimmers discovers existing tmux sessions but does not define layouts or startup commands (use tmuxinator for that)
• macOS and Linux only — tmux does not run on Windows, so neither does swimmers

FAQ

Why "swimmers"?

Sessions are fish. The TUI is an aquarium. Fish swim. Sessions swim between states.

Does it need Docker?

No. Single binary, flat-file persistence, talks to tmux directly.

Can I run the API without the TUI?

Yes. Run swimmers (or swimmers serve) on its own and use the REST endpoints directly, open the browser UI, or point a TUI at it via SWIMMERS_TUI_URL.

What happens when I close the TUI?

Your tmux sessions always keep running — the aquarium observes tmux, it doesn't own it.

In embedded mode (default), closing the TUI tears down its in-process API too, since they're the same process. The next swimmers-tui launch rediscovers tmux from scratch. In external mode (SWIMMERS_TUI_URL set), the standalone swimmers server keeps running independently; reopen the TUI to reconnect.

Can multiple TUIs connect to the same API?

Yes, via external mode. Run a standalone swimmers server and point each TUI at its URL via SWIMMERS_TUI_URL. Embedded mode is single-tenant by design — the API only exists inside that TUI process.

How does state detection work?

The SessionActor monitors each session's PTY output and classifies it into states (idle, busy, error, attention) based on shell activity patterns. Rest states (drowsy, sleeping, deep sleep) layer on top based on inactivity duration.

What is the thought rail?

A side panel in the TUI that displays AI agent thought streams. When a session runs Claude Code, Codex, or similar tools, their internal reasoning appears in the thought rail next to the aquarium view.

Is LocalTrust auth safe?

On loopback (127.0.0.1), yes — only processes on the same machine can reach the port. When you set SWIMMERS_BIND to a non-loopback address, the server refuses to start under AUTH_MODE=local_trust. Use AUTH_MODE=token with a strong AUTH_TOKEN for any external exposure.

Vision

See docs/VISION.md for the project's mission, competitive positioning, and strategic non-goals.

Design Philosophy

Sessions are living things. The aquarium metaphor is not decoration. It encodes session state into spatial position, animation speed, and sprite shape so you can assess a fleet of sessions with a glance instead of reading text.

The API is the truth. The TUI is a client. The API discovers tmux sessions, tracks their state, and serves snapshots. You can point multiple TUIs at the same API, run the API headless, or build your own client against the REST endpoints.

No infrastructure required. No database, no Docker, no message broker. The server binary talks to tmux directly via portable-pty, persists state to flat files under data/swimmers/, and serves HTTP on a single port.

Thoughts are first-class. The thought subsystem streams AI agent context (from Claude Code, Codex, etc.) into a side panel. Sessions that run AI coding agents surface their internal monologue alongside the terminal output.

About Contributions

Please don't take this the wrong way, but I do not accept outside contributions for any of my projects. Feel free to open issues — bug reports in particular are welcome. PRs are fine as a way to illustrate a proposed fix, but I won't merge them directly; I'll have Claude or Codex review and independently decide whether and how to address them.

License

MIT. See LICENSE.