procsi

Procsi is a terminal-based, project-scoped HTTP proxy with a powerful CLI & MCP server. Quickly intercept, inspect & rewrite HTTP traffic from the comfort of your terminal or favourite AI agent.

Feature Highlights

• Project-scoped — each project gets its own .procsi/ directory with a separate daemon, database, CA cert and interceptors
• MCP server — AI agents get full access to your captured traffic and can search, filter, inspect, mock — all via tool calls.
• Interceptors — mock, modify or observe traffic by writing typescript. Agent can do this over MCP meaning you can express complex scenarios in natural language!

Quick Start

npm install -g procsi

# Configure environment e.g. HTTP_PROXY
eval "$(procsi on)"

# Send a request
curl https://api.example.com/users

# Open UI
procsi tui

# Add MCP server to your AI tool
claude mcp add procsi -- procsi mcp

Browser Interception

Launch any browser pre-configured to route through procsi — no manual proxy setup, no certificate warnings:

# Auto-detect and launch your default browser
procsi browser

# Open a specific URL
procsi browser https://example.com

# Choose a specific browser
procsi browser --browser firefox
procsi browser --browser brave

Each browser session gets its own isolated profile and is automatically attributed in the TUI (e.g. source: chrome). Close the browser or press Ctrl+C to stop — the temp profile is cleaned up automatically.

Supported browsers:

| Engine | Browsers | | -------- | ------------------------------------------- | | Chromium | Chrome, Brave, Edge, Vivaldi, Arc, Chromium | | Firefox | Firefox, Zen Browser, LibreWolf |

Project Scoping

procsi doesn't use a global system proxy. Each project gets its own .procsi/ directory in the project root (detected by .git or an existing .procsi/):

your-project/
├── .procsi/
│   ├── interceptors/   # TypeScript interceptor files
│   ├── config.json     # Optional project config
│   ├── proxy.port      # Proxy TCP port
│   ├── control.sock    # IPC socket
│   ├── requests.db     # Captured traffic
│   ├── ca.pem          # CA certificate
│   └── daemon.pid      # Process ID
└── src/...

Separate daemon, database, certificates etc. You can run procsi in multiple projects at the same time without them interfering with each other.

For non-project contexts or custom setups, use --config to point directly at a data directory (no .procsi appended):

procsi --config /tmp/my-procsi-data on

See CLI Reference for the full resolution order (--config > --dir > auto-detect).

MCP Integration

procsi has a built-in MCP server that gives AI agents full access to your captured traffic and interceptor system.

Setup

Claude Code:

claude mcp add procsi -- procsi mcp

Codex:

codex mcp add procsi -- procsi mcp

Cursor — add to .cursor/mcp.json:

{
  "mcpServers": {
    "procsi": {
      "command": "procsi",
      "args": ["mcp"]
    }
  }
}

Other MCP clients (Windsurf, etc.) — add to your client's MCP config:

{
  "mcpServers": {
    "procsi": {
      "command": "procsi",
      "args": ["mcp"]
    }
  }
}

The proxy must be running (eval "$(procsi on)") — the MCP server connects to the same daemon as the TUI.

Available Tools

| Tool | Description | | ---------------------------- | ---------------------------------------------------- | | procsi_get_status | Daemon status, proxy port, request count | | procsi_list_requests | Search and filter captured requests | | procsi_get_request | Full request details by ID (headers, bodies, timing) | | procsi_search_bodies | Full-text search through body content | | procsi_query_json | Extract values from JSON bodies via JSONPath | | procsi_count_requests | Count matching requests | | procsi_clear_requests | Delete all captured requests | | procsi_list_sessions | List active proxy sessions | | procsi_list_interceptors | List loaded interceptors with status and errors | | procsi_reload_interceptors | Reload interceptors from disk |

See full MCP documentation for filtering, output formats, and examples.

Interceptors

TypeScript files in .procsi/interceptors/ that intercept HTTP traffic as it passes through the proxy. They can return mock responses, modify upstream responses, or just observe.

import type { Interceptor } from "procsi/interceptors";

export default {
  name: "mock-users",
  match: (req) => req.path === "/api/users",
  handler: async () => ({
    status: 200,
    headers: { "content-type": "application/json" },
    body: JSON.stringify([{ id: 1, name: "Alice" }]),
  }),
} satisfies Interceptor;

See full interceptors documentation for modify, observe, querying past traffic, handler context, and how they work.

How It Works

┌─────────────────────────────────────────────────────────────┐
│  Your Shell                                                 │
│  ┌─────────────────────────────────────────────────────┐   │
│  │  curl, wget, node, python...                        │   │
│  │          │                                          │   │
│  │          ▼                                          │   │
│  │  HTTP_PROXY=localhost:54321                         │   │
│  └─────────────────────────────────────────────────────┘   │
│                          │                                  │
└──────────────────────────┼──────────────────────────────────┘
                           ▼
┌─────────────────────────────────────────────────────────────┐
│  procsi daemon                                                │
│  ┌─────────────┐    ┌─────────────┐    ┌─────────────┐     │
│  │ MITM Proxy  │───▶│   SQLite    │◀───│ Control API │     │
│  │  (mockttp)  │    │  requests   │    │ (unix sock) │     │
│  └─────────────┘    └─────────────┘    └─────────────┘     │
└─────────────────────────────────────────────────────────────┘
                           ▲
                           │
┌──────────────────────────┼──────────────────────────────────┐
│  procsi tui                │                                  │
│  ┌───────────────────────┴─────────────────────────────┐   │
│  │ ● POST /api/users   │ POST https://api.example.com  │   │
│  │   GET  /health      │ Status: 200 │ Duration: 45ms  │   │
│  │   POST /login       │                               │   │
│  │                     │ Request Headers:              │   │
│  │                     │   Content-Type: application/  │   │
│  └─────────────────────┴───────────────────────────────┘   │
└─────────────────────────────────────────────────────────────┘

eval "$(procsi on)" starts a daemon, sets HTTP_PROXY/HTTPS_PROXY in your shell, and captures everything that flows through. eval "$(procsi off)" unsets them. The TUI connects to the daemon via Unix socket.

Environment Variables

eval "$(procsi on)" sets these in your shell (eval "$(procsi off)" unsets them):

| Variable | Purpose | | --------------------- | ------------------------------------ | | HTTP_PROXY | Proxy URL for HTTP clients | | HTTPS_PROXY | Proxy URL for HTTPS clients | | SSL_CERT_FILE | CA cert path (curl, OpenSSL) | | REQUESTS_CA_BUNDLE | CA cert path (Python requests) | | CURL_CA_BUNDLE | CA cert path (curl/Python fallback) | | NODE_EXTRA_CA_CERTS | CA cert path (Node.js) | | DENO_CERT | CA cert path (Deno) | | CARGO_HTTP_CAINFO | CA cert path (Rust Cargo) | | GIT_SSL_CAINFO | CA cert path (Git) | | AWS_CA_BUNDLE | CA cert path (AWS CLI) | | CGI_HTTP_PROXY | Proxy URL (PHP CGI, HTTPoxy-safe) | | PROCSI_SESSION_ID | UUID identifying the current session | | PROCSI_LABEL | Session label (when -l flag used) |

Additionally, procsi on sets PYTHONPATH, RUBYOPT, and PHP_INI_SCAN_DIR to load runtime-specific override scripts that ensure edge-case HTTP clients trust the proxy CA.

Configuration

Create .procsi/config.json to override defaults:

{
  "maxStoredRequests": 5000,
  "maxBodySize": 10485760,
  "maxLogSize": 10485760,
  "pollInterval": 2000
}

See full configuration documentation for details on each setting.

Supported HTTP Clients

Anything that respects HTTP_PROXY works. procsi sets the right CA cert env vars for each runtime automatically.

Works automatically (env vars only):

| Client | Support | | ------------------- | ------------------------------- | | curl | Automatic | | wget | Automatic | | Go (net/http) | Automatic | | Rust (reqwest) | Automatic | | .NET (HttpClient) | Automatic | | Deno | Automatic (DENO_CERT) | | Bun | Automatic (SSL_CERT_FILE) | | Git | Automatic (GIT_SSL_CAINFO) | | AWS CLI | Automatic (AWS_CA_BUNDLE) | | Cargo | Automatic (CARGO_HTTP_CAINFO) |

Works with procsi overrides (injection scripts):

| Client | Mechanism | | ---------------------------- | --------------------------------------- | | Node.js (fetch, axios, etc.) | NODE_OPTIONS --require preload script | | Python (requests, httplib2) | PYTHONPATH sitecustomize.py | | Ruby (Net::HTTP, gems) | RUBYOPT -r OpenSSL CA patch | | PHP (curl, streams) | PHP_INI_SCAN_DIR custom INI |

Not currently supported (needs system-level config):

| Runtime | Reason | | ------------- | -------------------------------------------- | | Java/JVM | Needs -javaagent or JVM trust store config | | Swift | Uses macOS Keychain only | | Dart/Flutter | Requires code changes for proxy | | Elixir/Erlang | Requires code changes for proxy |

TUI

j/k to navigate, Tab to switch panels, / to filter, e to export, Enter to inspect bodies, q to quit. Mouse support included.

See full TUI documentation for all keybindings and export features.

Documentation

• CLI Reference — all commands, flags, and examples
• Interceptors — mock, modify, observe, query traffic, handler context
• MCP Integration — tools, filtering, output formats, examples
• TUI — keybindings, export features
• Configuration — .procsi/config.json options

Development

git clone https://github.com/mtford90/procsi.git
cd procsi
npm install

npm run build        # Compile TypeScript
npm test             # Run all tests
npm run typecheck    # Type checking only
npm run lint         # ESLint
npm run dev          # Watch mode

Troubleshooting

Certificate errors

procsi sets common CA environment variables automatically, but some tools need manual configuration:

cat .procsi/ca.pem

Daemon won't start

Check if something else is using the socket:

procsi status
procsi daemon stop
eval "$(procsi on)"

Requests not appearing

Your HTTP client needs to respect proxy environment variables.

There are workarounds implemented for node - e.g. fetch override. Other libraries in different environments may need a similar treatment.

Acknowledgements

procsi is built on top of MockTTP by Tim Perry, the same MITM proxy engine that powers HTTP Toolkit.

Licence

AGPL-3.0-or-later