railmux 0.2.0

Terminal UI to navigate, resume, and start Claude Code and Codex sessions

Railmux — session manager for Claude Code & Codex

A terminal UI to navigate, resume, and start Claude Code and Codex sessions across all your projects. Railmux lives in the left pane of a tmux window; the right pane shows the active agent. Each session runs in its own detached tmux session, so switching never interrupts in-progress responses or tool calls.

• Claude Code mode — reads ~/.claude/projects/*, lists sessions by project, resume with claude --resume
• Codex mode — reads ~/.codex/sessions/*, same sidebar workflow for Codex sessions
• Press m to cycle through the available modes

Why Railmux?

Without Railmux, managing multiple agent sessions means manually tracking tmux windows, remembering which session lives where, and copy-pasting session IDs. Sessions pile up across projects, context gets lost, and switching between them is friction.

Railmux replaces all of that with a single keystroke:

• One sidebar, all sessions — browse every Claude Code and Codex session across every project, filter by name, star favourites
• Instant switching — press Enter and the right pane attaches to a different background tmux session; every agent keeps running, no responses lost
• Zero manual bookkeeping — no more tmux ls | grep cc- or hunting through ~/.claude/projects/

Quick start

pip install railmux
# or: pip3 install railmux
railmux

Requires Python 3.9+, tmux, less, and at least one supported agent CLI on PATH. Claude Code and Codex are independent: a missing provider does not stop you from using the other one.

If tmux is missing, an interactive Railmux launch can offer to install it with Homebrew on macOS or apt-get on Debian/Ubuntu/WSL. Railmux shows the exact command and requires explicit confirmation (default: no); it never installs Homebrew itself or modifies the system during non-interactive runs. Other common Linux package managers receive a copyable installation command.

If you are not already inside tmux, Railmux launches its own tmux session. Run railmux --doctor for a privacy-safe dependency and environment report when setup does not behave as expected.

Keys

Navigation

Key	Action
↑ / ↓	Move selection within the focused pane
Tab / Shift-Tab	Cycle focus through Projects, Sessions, Running panes
Ctrl-B Tab	Toggle directly between the sidebar and Target pane
Esc	Move focus up: Running → Sessions → Projects
/	Filter the focused Projects, Sessions, or Running pane by name

Session actions

Key	Action
Enter	Resume or start the selected session
n	Start a fresh session in the current project
i	Popup with session details
r	Rename the focused session
s	Toggle star — starred sessions pinned to top with ⭐
k	Kill the running agent process (keeps session file)
d	Delete the focused session (prompts for confirmation)
t	Open a terminal in the active project directory
m	Cycle through available agent modes
␣	Preview stopped or switch running target (like single-click)
F8	Cycle agent layout: single → side-by-side → stacked
F9	Fullscreen the agent pane (toggle) for clean text selection
?	Full help popup with all keybindings
q or Ctrl-C	Quit with confirmation

+ New project works in both Claude Code and Codex modes. Browse to an existing directory and choose . (use this path), or type a new relative, absolute, or ~-based path. When no existing entry matches, select the explicit + create … row (it is focused automatically) and press Enter; railmux creates the directory before starting the agent.

The rename popup starts with the current title pre-filled. Press Ctrl-U to clear the entire input, Enter to save a non-empty title, or Esc to cancel.

Dual-agent layouts

Railmux distinguishes the Focused pane from the Target pane. The Focused pane receives keyboard input; the Target pane is where actions started from the sidebar take effect. They can differ while you browse the sidebar.

Open the first agent normally, then press F8 to cycle through single, side-by-side, and stacked layouts. Pane 2 can remain empty until you choose a session for it, and layouts that do not fit the terminal are skipped. Returning to single leaves Pane 2's agent running in the background.

In a split, focus an agent pane to make it the Target pane. After focus returns to the sidebar, single-click or ␣ acts in that pane without moving keyboard focus; double-click or Enter opens there and transfers focus. The status bar at the bottom-left shows the current layout and Target pane:

Symbol	Meaning
▣	Single pane
◧ / ◨	Side-by-side, targeting left / right
⬒ / ⬓	Stacked, targeting top / bottom

Agent borders turn green around the Focused pane. When focus is in the sidebar, the borders return to gray while the status symbol continues to show the Target pane. Ctrl-B Tab returns directly from either agent pane to the sidebar without changing that Target, then toggles back to it. Ctrl-B plus an arrow remains spatial: left/right moves across a side-by-side split, while up/down moves between stacked agent panes.

Finding running sessions

Plain text matches the visible session label, project, and provider without searching message content. Add project:<name> to restrict the list to one project. Claude Code and Codex keep independent Running filters, and blocked sessions move ahead of the other results.

Mouse

Action	Effect
Left-click (non-running)	Preview session history in the Target pane
Left-click (running)	Switch the Target pane to that session
Double-click	Open/attach in the Target pane and move focus there
Right-click	Context menu (Open, Preview, Info, Rename, Star, Kill, Term, Delete)

The terminal must report mouse buttons to applications for these actions to reach Railmux. Right-click reporting is sometimes a separate setting from ordinary mouse reporting; see FAQ 2.

History preview

For a stopped session, left-click or press ␣ to view conversation history in the Target pane without starting or resuming the agent. Preview is read-only: it cannot send a message or change the session. User and assistant messages, tool calls, and abbreviated tool output are colour-coded, while internal context and encrypted reasoning are hidden.

Preview opens at the latest activity in less; large sessions are limited to their latest 2,000 saved records. Press / to search, n/N to move between matches, and q to exit and restore the pane. Double-click to skip preview and open the session directly.

For a running session, single-click or ␣ switches the Target pane to it while focus stays in Railmux. For a stopped session, the same inputs open a read-only preview. Double-click or Enter opens either kind and transfers focus. The context-menu Preview action follows the single-click/␣ rule.

Status indicators

Each running session shows a coloured ● reflecting its current state:

• Green — idle (assistant last responded normally)
• Yellow — busy (assistant is processing)
• Red — blocked (waiting for tool approval)

An independent magenta ! marks an outcome that still needs attention, such as an abort or provider error. It does not replace the activity dot: a live session can be idle and still show !, while a stopped historical session keeps its neutral ○ marker alongside the badge. Session Info and Running Info show the available details.

A grass-green title identifies a live tmux session independently of its status; stopped sessions use a neutral hollow ○. The same grass green is used for the focused pane chrome and tmux status bar. The current cursor uses a deeper green background, while the session displayed in the agent pane remains marked in neutral slate after keyboard focus moves away.

Sessions and restarts

Each opened agent runs in a detached tmux session, so switching sessions does not interrupt it. To leave agents running when you quit Railmux, press s for soft quit in the confirmation popup; restarting the same Railmux instance then restores the usable workspace when those sessions are still available. A normal quit confirmation ends all running sessions instead.

If Railmux stops while a provider is still creating a new session, the Running pane may show it as unresolved. You can reopen or stop that agent, but Railmux will not offer to delete provider history until it can identify the session safely.

Configuration

Optional config at ~/.config/railmux/config.toml:

[claude]
# Path to the claude binary (default: "claude")
binary = "claude"

[codex]
# Path to the codex binary (default: "codex")
binary = "codex"
home = "~/.codex"

[projects]
# Show projects with no resumable sessions (default: false)
show_empty_projects = false

[live]
# How often to refresh the session list (ms)
poll_interval_ms = 1000

# Agent display mode (default: "swap").
# Set "nested" only when troubleshooting an unusual tmux environment.
agent_transport = "swap" # or "nested"

Most users should leave agent_transport unchanged. Railmux automatically uses the compatible nested display when the default swap mode is not safe for the current tmux environment.

Diagnostics

railmux --doctor

The doctor command works even when tmux is missing. It reports component versions, terminal capability hints, configuration health, and whether provider data directories are accessible. Its output is designed for issue reports: it does not include hostnames, usernames, session IDs, transcripts, credentials, environment values, configured commands, or raw custom paths.

FAQ

1. How do I copy text from the agent pane?

Under tmux the sidebar and agent share the screen, and over SSH your clipboard lives on the local machine.

OSC 52 (iTerm2, kitty, WezTerm, Alacritty, foot, Windows Terminal): drag-select in the agent pane copies to the local clipboard automatically, even over SSH, no Shift needed. (iTerm2: enable Settings → General → Selection → "Applications in terminal may access clipboard".)

Without OSC 52 (Terminal.app, etc.): press F9 to fullscreen the agent → Shift‑drag to select → Cmd+C / Ctrl+C to copy → F9 to return.

Ctrl-B z also toggles fullscreen (built into tmux) but zooms whichever pane has focus — it may fullscreen the sidebar instead of the agent.

2. Mouse buttons or F8/F9 don't work — what's wrong?

These are usually terminal‑side settings, not tmux or railmux.

Mouse: enable your terminal's “Report mouse events” or “Mouse reporting” setting. Railmux already enables tmux mouse support for its own sessions, but it cannot receive an event that the terminal keeps for its own UI.

Right-click may have a separate forwarding switch. In iTerm2, open Settings → Pointer → General, then enable “Right click reported to apps, does not open menu.” Without it, iTerm2 opens its own menu instead of sending the click to Railmux.

VS Code and Cursor users can change Terminal › Integrated: Right Click Behavior when the editor's own menu prevents right-click from reaching Railmux. copyPaste is the recommended starting point: Railmux handles right-click while its mouse-aware sidebar is active, and the editor retains its convenient copy/paste behavior elsewhere in the terminal. Cursor exposes the same VS Code setting. Configure it in User Settings JSON:

{
  "terminal.integrated.rightClickBehavior": "copyPaste"
}

Use nothing instead if your editor version still intercepts right-click or you prefer all right-click events to pass directly to terminal applications.

F8 (layout) and F9 (fullscreen): the operating system or terminal may consume function keys before tmux sees them. On macOS, either hold Fn when pressing the key or enable System Settings → Keyboard → “Use F1, F2, etc. keys as standard function keys”; also remove any Mission Control shortcut using the same key. On Windows laptops, Fn+Esc commonly toggles Fn Lock. If the terminal has its own shortcut or key-mapping editor, remove the conflicting mapping or configure it to send the corresponding F8/F9 function-key sequence to the terminal session.

3. Using railmux over SSH

railmux works over SSH out of the box, including mouse scrolling in the agent pane. These tweaks improve responsiveness and scrollback:

Server (~/.tmux.conf on the remote machine):

set -sg escape-time 0         # eliminate delay after Escape key
set -g  history-limit 10000   # generous scrollback per pane

Client (~/.ssh/config on your local machine):

Host your-server
    Compression yes           # smoother tmux pane scrolling over SSH

If the connection is so slow that the sidebar can't refresh one frame per second, skip the mouse and use keyboard navigation — ↑↓ / Tab / Enter cover every operation and don't depend on a fast redraw.

4. Will automated review sessions pollute my session list?

Codex: sessions created by codex exec (headless automation, pre‑commit hooks, CI) are filtered automatically — railmux only shows interactive sessions (codex-tui, codex_cli_rs).

Claude Code: for one-shot automated reviews, disable session persistence so the consultation never appears in /resume:

# Print mode only; the review is not saved as a resumable session
claude -p --no-session-persistence "review this diff"

(--no-session-persistence is a Claude Code print-mode option.)

5. pip reports "externally-managed-environment"

Create a virtual environment, then install Railmux with that environment's pip. This works on macOS, Linux, and WSL without modifying the system Python:

python3 -m venv ~/.venvs/railmux
source ~/.venvs/railmux/bin/activate
pip install railmux

pipx install railmux is an optional convenience for a globally available CLI; it is not required on macOS or any other platform.

Acknowledgements

The tmux sidebar idea and initial architecture came from regmi-saugat/ccmgr. railmux extends it with Codex support, session history preview, starring, in-app renaming, mouse interaction, and a status bar integrated into the tmux status line.

Contributing

Contributions are welcome; see CONTRIBUTING.md.