SubMon

Some say bug bounty isn't just about finding bugs, but being the "first" to find them. I'm building this tool to notify hunters when new subdomains appear.

Features

• You can add your favorite target: name + domain.
• Then you can either click scan or schedule a scan.
• When the scan finishes, you will get a discord alert.
• If you set up the scheduler, you will get a discord notification every time it finds new subdomains.

• Here you can see result from the last scan: which subdomain is new, which is missing.
• You will also see the title of that subdomain, but it might not be accurate.

Tech Stack

Backend: FastAPI

• ORM: SQLModel
• Data validation: Pydantic
• SQL DB: SQLite

Frontend: React

• ViteVibe coding

Scanning Tools

• subfinder
• dnsx
• httpx

Try It Yourself

• Making A Discord Webhook

Manual Install

cd backend

# install tools
go install -v github.com/projectdiscovery/subfinder/v2/cmd/subfinder@latest
go install -v github.com/projectdiscovery/dnsx/cmd/dnsx@latest
go install -v github.com/projectdiscovery/httpx/cmd/httpx@latest

# add GOPATH/bin to PATH
export PATH=$PATH:$(go env GOPATH)/bin
# save the above command to `~/.bashrc`
source ~/.bashrc  # or ~/.zshrc

# optional env vars for backend
export DB_NAME="database.db"
export DISCORD_WEBHOOK_URL="YOUR-DISCORD-WEBHOOK"

# create a virtual env
python -m venv venv
source venv/bin/activate
pip install -r requirements.txt

# run fastapi service
python -m app.main

# run worker in a new terminal
python -m app.services.worker

# check Swagger doc
http://localhost:8000/docs

# check ReDoc
http://localhost:8000/redoc

cd frontend

# run frontend
npm i
npm install node
npm run dev

Docker Compose (recommended)

From the project root:

# optional: create env file and set Discord webhook for alerts
cp .env.example .env
# then edit .env and set DISCORD_WEBHOOK_URL

# build and start frontend + backend + worker
docker compose up --build -d

Open:

• Frontend: http://localhost:5173
• API docs: http://localhost:8000/docs

# stop services
docker compose down

Workflow

flowchart TD
    U[User / Frontend] -->|Scan Target| A[FastAPI Backend]
    U -->|Schedule Scan| A

    A -->|Create or update ScanRun = queued| DB[(SQLite)]
    W[Worker Loop] -->|Poll queued jobs + enqueue due schedules| DB
    W -->|Pick next queued ScanRun| S[Scanner Pipeline]

    S --> SF[subfinder]
    SF --> DX[dnsx]
    DX --> HX[httpx]
    HX --> D[Diff with existing subdomains]

    D -->|Insert new subdomain| DB
    D -->|Mark missing subdomain| DB
    D -->|Send new findings| DIS[Discord Webhook]

    S -->|success / failed| W
    W -->|Update ScanRun status| DB

Loading

1. Frontend triggers scan or schedule endpoints.
2. API stores state in ScanRun (queued, running, success, failed).
3. Worker loops through queued and scheduled jobs.
4. Scanner runs subfinder -> dnsx -> httpx, diffs results, updates DB, and sends Discord alerts for new subdomains.

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• Release notes