loopback

Self-hosted webhook testing tunnel like ngrok but with replay, inspection, programmable transformations... AND a chaos mode that randomly delays, drops, or corrupts requests.

Language: Elixir
Constraint: Hostile UI
Stack: Phoenix, LiveDashboard, GenServer, Bandit

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Features

• Public URL tunnel to local HTTP server
• Request replay and inspection UI
• Programmable transformations (Lua/Elixir scripting)
• Chaos mode: random delays, drops, corruption
• Phoenix LiveDashboard for monitoring
• Request history with search and filter
• Webhook signature verification helpers

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Development Plan

1. Phase 1: Phoenix app scaffold with LiveDashboard
2. Phase 2: Tunnel core — public URL → local forward
3. Phase 3: Request capture and storage (ETS + persistence)
4. Phase 4: Inspection UI (LiveView)
5. Phase 5: Replay engine (exact + modified replays)
6. Phase 6: Programmable transformations
7. Phase 7: Chaos mode GenServer (configurable probabilities)
8. Phase 8: Webhook signature verification helpers

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Getting Started

Prerequisites

• Elixir toolchain

Build

cd loopback
mix deps.get
mix compile

Run

mix phx.server

Create a tunnel

With the server running, open an IEx shell and create a tunnel:

Loopback.Tunnels.create_tunnel("http://localhost:3000")
# => {:ok, %Loopback.Tunnels.Tunnel{id: "0001", target_url: "http://localhost:3000", ...}}

Requests to http://localhost:4000/t/:tunnel_id/*path are forwarded to the tunnel's target_url.

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Architecture

See PLAN.md for detailed architecture decisions and implementation notes.

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License

Apache-2.0

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