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Open source · v1.8.6

The mainframe, in a browser tab

No emulator install. No thick client. Open a tab, connect to any TN3270 host, and work exactly like you would at a real 3270 terminal — then let AI Chat, chaos exploration and workflow recording do the heavy lifting.

Install and run Connect a host REST API

session · tn3270 model 2 · 24×80 
$ curl -fsSL https://3270Web.3270.io/install.sh | bash
› method     binary · docker · compose  [ask]
› listening  http://localhost:3270      [up]
› connect    mvs.example.com:992        [ok]
› negotiate  IBM-3278-2-E              [tn3270e]
› recording  12 actions captured       [rec]
›
Install steps1binary, Docker or Compose
Client software0any modern browser
Bundled fonts3IBM 3270 web faces
Export targetJSONreplayable by 3270Connect

Feature Highlights

  • AI Chat Mode

    Drive any 3270 session by typing plain English. The AI reads the current screen, proposes field fills and key presses, and waits for your approval before acting. Toggle Auto Mode to let it run hands-free. Bring your own AI: GitHub Copilot, Claude, OpenAI, Google AI, Ollama, or any OpenAI-compatible endpoint.

    AI Chat Mode

  • Chaos Exploration

    Auto-discover every navigation path on a host. Chaos mode fills fields with generated values, presses AID keys, and records every screen transition — then exports a reusable workflow JSON ready for load testing with 3270Connect.

    Chaos Mode

  • Workflow Recording & Playback

    Capture terminal actions as portable JSON. Replay them with a single click, step through them one action at a time in debug mode, or hand the file to any CI pipeline.

    Recordings and Playback

  • REST API

    Connect, read screens, submit input, and control chaos runs over HTTP. Wire 3270 sessions into any automation stack — scripts, pipelines, or custom tooling.

    REST API

  • Host Compatibility Profiler

    Probe any TN3270 host and capture its negotiated terminal model, protocol options, capabilities, and timing as a JSON document. Same schema as 3270Connect -profile, so profiles diff cleanly across tools and environments.

    Host Compatibility Profiler

  • Chaos Mind-Map Compare

    Diff two previously-exported chaos mind maps to surface field and transition divergence between hosts — ideal for migration-readiness checks against Rocket Enterprise Server stand-ins.

    Chaos Mind-Map Compare

  • IBM 3270 Terminal Fonts

    Three bundled 3270-style web fonts (Regular, Semi-Condensed, Condensed) make the browser session look like a real 3279 display on any platform — no install, no CDN fetch.

    Terminal Fonts

  • Command Palette

    Press Ctrl+K from anywhere — even mid-keystroke in the terminal — to search every menu and modal action, jump straight to a chaos or recording control, and switch themes without opening Settings.

    Command Palette

Screenshots

Connect screen

Connect to any TN3270 host, a saved profile, or a bundled sample app.

Session screen

A live session in the default Yorkshire Mainframe Terminal theme.

Command palette

++ctrl+k++ searches every action, including everything inside the menus.

AI chat side panel

The AI chat panel, ready to connect a provider. Drag its edge to resize.

Logging screen

The log viewer, available when Allow log access is enabled.

Sample app

Sample App 1 running against the bundled go3270 example server.

First Session

  1. Get 3270Web running — native Linux binary, Docker, or Docker Compose.
  2. Open 3270Web in your browser (http://localhost:3270).
  3. Enter your TN3270 host and port on the connect screen. No mainframe? Enter sampleapp:petstore for the bundled pet store — a counter, a back office and a command line on every screen. See Bundled Sample Applications.
  4. Use the terminal — keyboard shortcuts, PF keys, and field navigation all work as expected.
  5. Optional: hit Start recording to capture the session for replay later.

Install and Run    Full setup guide

What's in This Guide

Section What you'll find
Install and Run Run the native Linux binary, Docker image, or Docker Compose
User Accounts and Sign-In Turn on accounts, create the first administrator, manage people
Running a Shared Instance What one account is kept from another, API tokens, host allowlist, rate limits, the audit trail
Connect and Use 3270Web Host configuration, startup options, UI tour
Recordings and Playback Record, load, play, debug, and export workflows
Chaos Mode Automated screen exploration and load-test export
AI Chat Mode Conversational session control
AI Providers Point AI Chat at Copilot, Claude, OpenAI, Google AI, Ollama, or your own endpoint
Keyboard and Controls Full keyboard shortcut reference
Screen Size and Model Guide 3270 model limits and field size rules
REST API Endpoint reference for scripting and CI
Host Compatibility Profiler Probe a host once and capture its CompatibilityProfile JSON for cross-environment comparison
Chaos Mind-Map Compare Diff two exported mind maps to surface divergence between hosts
Terminal Fonts Bundled IBM 3270-style web fonts and how to switch between them
Compatibility Profile Schema Field-by-field reference for the shared profile JSON (v1.0.0)
Feature Roadmap Planned and in-progress features
Acknowledgements s3270 and the x3270 family, whose protocol work 3270Web is built on