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Start the MITM proxy and configure environment variables for HTTP/HTTPS interception
Install with Codex or Claude Copy this prompt, paste it into Codex, Claude, or another assistant, and let it review the skill page and install it for you.
Based on SOC occupation classification
| name | mitm-start |
| description | Start the MITM proxy and configure environment variables for HTTP/HTTPS interception |
| disable-model-invocation | true |
| argument-hint | [port] |
| allowed-tools | Bash(bash *) Bash(curl *) Bash(npx *) |
Start the @withseismic/mitm proxy and configure the shell to route traffic through it.
npx @withseismic/mitm --headless &
The --headless flag runs the proxy and API server without the terminal UI. This is required when launching from scripts, CI, or Claude Code. Headless mode also auto-activates when no TTY is detected.
The proxy listens on two ports:
export HTTP_PROXY=http://127.0.0.1:8888
export HTTPS_PROXY=http://127.0.0.1:8888
Most HTTP clients (curl, node-fetch, axios, etc.) will respect these variables automatically.
curl -s http://localhost:8889/api/status | cat
Expected response:
{
"proxyRunning": true,
"proxyPort": 8888,
"ruleCount": {
"file": 0,
"api": 0,
"breakpoints": 0,
"blocks": 0,
"redirects": 0
},
"requestCount": 0
}
| Flag | Description |
|---|---|
--headless | Run without terminal UI (proxy + API only) |
--skip-setup | Skip interactive CA certificate setup |
--port <n> | Override default proxy port (8888) |
--api-port <n> | Override default API port (8889) |
Start, verify, and export env vars in one step:
source <(bash skills/mitm-start/scripts/proxy-up.sh)
This will start the proxy if not running, wait for it to come up (max 10s), and print export statements. Use source <(...) to apply the env vars to the current shell.
.certs/ on first run. You may need to trust this CA in your browser or OS to intercept HTTPS without warnings.127.0.0.1 only — not exposed to the network.kill %1 or find it with lsof -i :8888.Introduces the @withseismic/mitm proxy plugin — explains available skills, scripts, the REST API, rule engine, and traffic inspection. Use when a user asks what the MITM proxy can do, how to get started, or needs an overview of capabilities.
Inspect captured HTTP traffic from the MITM proxy. Use when the user wants to see what requests were made, filter traffic by URL, view request/response details, or analyze network activity.
Create and manage MITM proxy interception rules and transforms. Use when the user wants to intercept, modify, block, redirect, or mock HTTP traffic passing through the proxy.
Check MITM proxy status, rule counts, and request statistics. Use when the user asks if the proxy is running or wants to see current state.