PyFuzz: Enhancing the API Fuzzer

Hey there, fellow tech enthusiasts! Following up on my previous post about PyFuzz, I wanted to share some recent enhancements I've made to the tool. These updates aim to make PyFuzz more robust, flexible, and user-friendly for API endpoint enumeration. Let's dive into what's new.

Why the Enhancements?

After using PyFuzz for a while and receiving feedback from the community, I realized there were areas where the tool could be improved. Specifically, I wanted to:

Handle rate limiting more gracefully to avoid overwhelming target servers.
Provide more control over which HTTP status codes are considered successful.
Improve error handling to make the tool more resilient during scans.

With these goals in mind, I set out to implement the following features.

New Features

1. Rate Limiting

APIs often implement rate limiting to prevent abuse. Previously, PyFuzz didn't account for this, which could lead to 429 Too Many Requests errors. To address this, I've added a rate-limiting feature that introduces a brief delay between requests:

# Optional: In a future CLI-enhanced version
python fuzz.py --rate 5

This helps stay within acceptable request thresholds for most APIs, preventing you from getting temporarily blocked during testing.

2. Customizable Success Status Codes

Not all APIs use standard 200 OK responses for successful endpoints. Some might return 302, 403, or even 500 in specific cases. So, I added internal logic to only print non-404 responses, and in the future, this will be customizable:

# Hypothetical future CLI version
python fuzz.py --success-codes 200,302,403

Right now, the fuzzer prints everything that's not a 404 — which keeps the output focused on potentially interesting endpoints.

3. Enhanced Error Handling

Previously, a single timeout or bad response could disrupt the scan. That's been fixed with a more robust approach:

Timeout? Retry once.
ConnectionError? Retry.
JSON decode error? Gracefully fallback and log.
Keyboard interrupt? Clean exit.

This made PyFuzz far more usable in real-world conditions where network reliability isn't guaranteed.

🧩 Tricky Struggles Along the Way

No devlog is complete without a few hiccups. Some of the challenges I ran into:

→ Logging vs Output

At first, I had everything printing to the terminal — but it quickly became noisy. I had to split meaningful user-facing output from internal logs using the logging module. This was a learning curve, but totally worth it for cleaner results.

→ Tqdm Progress Woes

Getting tqdm to play nicely with multithreaded execution took a bit of trial and error. Ensuring the progress bar didn't glitch while threads were printing was annoying — had to rework the way results were collected and printed after the scan finished.

→ Rate Limit Detection

Catching 429 responses is one thing — but deciding what to do next was another. I settled on a simple sleep+retry for now, but smarter backoff handling is still on the roadmap.

→ JSON Hell

Some endpoints returned HTML even with a 200 status code, which made .json() crash. Wrapping that in a try/except was simple, but it reminded me that not all "working" endpoints are nice or predictable. It's the real world, after all!

How to Use the Enhanced PyFuzz

Step 1: Clone the Repository

git clone https://github.com/Kushal-39/PyFuzz----simple-python-api-fuzzer.git
cd PyFuzz----simple-python-api-fuzzer

Step 2: Install Dependencies

pip install requests tqdm

Step 3: Run the Script

python fuzz.py

You'll be prompted to enter the base URL. The script will read your wordlist, check for valid endpoints, and only display useful results — no clutter.

Looking Ahead

These changes have made PyFuzz much more practical for day-to-day API recon. In future updates, I'm planning to:

Add CLI support using argparse
Export results to JSON or TXT
Add method fuzzing support (POST, PUT, etc.)
Maybe even add proxy and header options

Final Thoughts

This round of enhancements made PyFuzz feel more like a proper tool and less like a one-off script — and that's a great feeling. The journey from "it works on my machine" to "it works reliably for everyone" is always longer than expected, but hugely satisfying.

Thanks for following along the journey. If you try it out, have ideas, or want to nerd out about API fuzzing — feel free to reach out. The project's open-source and always evolving.

As always: use responsibly, fuzz ethically. Your freedom is worth more than a CVE!

PyFuzz: Enhancing the API Fuzzer with New Features