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Connect and Use 3270Web

This page explains connection setup and the full Settings modal from a user perspective.

Connect to a Host

You can connect to:

  • hostname:port (example: mainframe.example.com:23)
  • IPv4:port (example: 10.0.0.5:23)
  • IPv6:port (example: [::1]:23)
  • sampleapp:<id> for bundled sample targets

If autoconnect is enabled, 3270Web will connect automatically on startup.

Open Settings

  1. Click the Settings icon in the toolbar.
  2. Use tabs to switch sections.
  3. Edit values.
  4. Click Save settings.
  5. If prompted, restart 3270Web to apply startup-level changes.

You can also use:

  • Refresh to reload current values
  • Reset to defaults inside each settings section
  • Maximize for easier editing of long values

Toolbar Callouts

Toolbar screenshot

  1. Disconnect
  2. Logs
  3. Settings
  4. Start recording
  5. View recording (when a recording is loaded)

Settings Modal Callouts

Settings modal screenshot

  1. Refresh values
  2. Maximize/restore modal
  3. Close settings
  4. Section tabs
  5. Active section content
  6. Reset section to defaults
  7. Save settings

Settings Sections (Full)

Connectivity

Controls how 3270Web reaches the host.

Includes:

  • Port, connect timeout
  • IPv4/IPv6 preference
  • Proxy settings
  • callback/script port and socket options

Use this section when you need alternate network routing or script protocol listeners.

TLS/Security

Controls TLS certificate and protocol behavior.

Includes:

  • Certificate verification toggle
  • Min/max TLS protocol
  • Client certificate and key files
  • CA file/directory/chain
  • Accepted hostname and client certificate name

Use this when connecting to secured hosts with custom certificate requirements.

Emulation

Controls terminal identity and data representation.

Includes:

  • Terminal model (3278/3279 variants)
  • Host code page
  • Terminal/device/user identity options
  • NVT mode and oversize behavior

This section directly affects screen size, field positions, and recording reliability.

Automation/Startup

Controls startup and command automation behavior.

Includes:

  • Exec command override
  • Login macro
  • HTTPD binding
  • Minimum required s3270 version

Use this for scripted startup flows and custom launch behavior.

Diagnostics

Controls trace and diagnostic output.

Includes:

  • Trace enable/disable
  • Trace file and max size
  • Help/version/unit-test environment flags

Use this section when troubleshooting host interaction issues.

App

Controls application-level UI features.

Includes:

  • Allow log access
  • Use keypad (show virtual keypad by default)
  • Terminal Font dropdown — pick from the three bundled IBM 3270-style fonts (Regular, Semi-Condensed, Condensed). See Terminal Fonts for usage notes.

Use this section to control log visibility and default keyboard UI behavior.

Chaos

Controls chaos exploration defaults.

Includes:

  • CHAOS_MAX_STEPS
  • CHAOS_TIME_BUDGET_SEC
  • CHAOS_STEP_DELAY_SEC
  • CHAOS_SEED
  • CHAOS_MAX_FIELD_LENGTH
  • CHAOS_LEARNED_INPUT_REUSE_BIAS (default 1.0) — weight applied to known-good input values when generating new field writes.
  • CHAOS_LEARNED_KEY_REUSE_BIAS (default 1.0) — how often the engine retries AID keys that have previously caused a transition versus exploring untried keys.
  • CHAOS_EXPORT_SUCCESS_BALANCE (default 1.0) — when exporting the chaos workflow JSON, balances steps drawn from successful transitions against exploratory steps.
  • CHAOS_OUTPUT_FILE
  • CHAOS_EXCLUDE_NO_PROGRESS_EVENTS

Use this section to tune how aggressively chaos mode explores screens and where optional output should be written. See Chaos Mode for a deeper walkthrough of the bias settings.

UI Conveniences

A few quality-of-life behaviours worth knowing about:

  • Collapsible toolbar sections — the Recording and Chaos toolbar groups collapse with a chevron and remember their state, so a busy toolbar can be trimmed to just the controls you care about.
  • Required hostname input — the connect form marks the hostname field as required and announces missing-value errors to assistive tech, so it is harder to accidentally submit an empty form.
  • Saved host deletion confirmation — removing a saved host profile pops a confirmation modal; the destructive action cannot fire on a single mis-click.
  • Destructive disconnect styling — the Disconnect toolbar button is visually tagged as destructive (warning tint at rest) so it is distinct from the safer navigation buttons next to it.
  • Toast notifications — short-lived theme-aware toasts surface the result of background actions (save, export, error) without taking focus.

Log Access

If log access is enabled in settings, you can open the Logs modal from the toolbar and:

  • Turn verbose logging on/off
  • Refresh logs
  • Copy/download logs
  • Clear logs

Best Practices

  • Keep one known-good model/code page profile per host environment.
  • Apply TLS changes carefully and verify certificate paths.
  • Prefer debug playback for new recordings before running full play mode.