Configuration

Postbin Ultra is configured entirely through the in-app Settings dialog (open with , or click the cog in the top bar). Settings are persisted as JSON in a platform-standard config directory and applied on Save without restarting the capture server.

#Settings file

Platform Path
macOS ~/Library/Application Support/PostbinUltra/settings.json
Linux $XDG_CONFIG_HOME/postbin-ultra/settings.json (defaults to ~/.config/postbin-ultra/settings.json)
Windows %APPDATA%\PostbinUltra\settings.json

The file is written atomically — Postbin writes to a sibling .tmp and renames into place, so a crash mid-write never leaves you with a half-written file. Missing or unreadable file → defaults are used and the file is recreated on next Save. Unknown fields (e.g. ui_port from pre-2.0 installs) are silently dropped.

#Settings → Capture

Field Default Notes
Bind address 127.0.0.1 IP the capture server listens on. 0.0.0.0 to accept from anywhere on the network — only do this on a trusted LAN.
Port 9000 TCP port. The supervisor walks up to 50 ports looking for the next free one if this is busy; the actual bound port is shown in the top bar. 0 means "any free port."
Buffer (requests) 1000 Bounded ring buffer size. Once full, the oldest request is evicted. Larger values use more RAM but let you scroll back further.
Max body size 10485760 (10 MiB) Bodies larger than this are truncated. Truncated bodies show a [truncated] warning in the row and the detail header; forwarding is skipped to avoid corrupting upstream's view.

Saving Bind / Port reconfigures the running capture server in place — no restart needed.

#Settings → Forward

Field Default Notes
Forward each captured request upstream off Master toggle for proxy mode. When on, every captured request is also relayed to the upstream and the upstream's response is shown back to the client.
Upstream URL — The base URL. Captured request's path + query are appended.
Timeout 30 s Per-request timeout for the upstream.
Skip TLS verification (dev only) off Accept self-signed certs.

Full guide: Forward + replay.

#Settings → Appearance

Three big tappable cards:

Theme also cycles with t when no input has focus.

#Settings → Advanced

Field Default Notes
Log file (none) Path to a file Postbin appends every captured request to as JSON-lines (one request per line). Useful for piping captures into another tool or feeding them to a coding agent watching alongside you.
Skip update check on startup off When off, Postbin makes a single GitHub API call at launch to look for newer releases. Off-by-default since the call is best-effort and silently swallows any failure.
Check for updates (button) Manual check on demand — opens the release page in your browser if a newer version exists.

#Hot-reload semantics

Most fields take effect immediately on Save:

The settings file is rewritten atomically on every Save.

#Resetting

Reset to defaults in the Settings dialog wipes every field back to the table above. Cancel discards your in-flight edits. There's no undo on Save — the previous settings are overwritten.

#Per-request size budget

Captured requests live in RAM in a Vec<CapturedRequest> capped at the Buffer (requests) size. A naive upper-bound on memory is buffer_size × max_body_size + headers. With defaults that's 1000 × 10 MiB = 10 GiB worst case, but real workloads usually average a fraction of max body. Adjust both knobs to suit.

#Next