Find Undocumented API Endpoints in 5 Minutes

Undocumented (or “hidden”) API endpoints often called shadow APIs represent one of the biggest risks in modern web applications. These endpoints are not listed in official documentation, yet they still respond to requests. Attackers love them because they frequently lack proper authentication, rate limiting, or input validation.

The good news? You can discover many of them in under 5 minutes using free or low-cost modern tools. Website owners, developers, penetration testers, and security teams must stay vigilant regarding security of websites as well as data privacy of users who visit these websites, by addressing the presence of undocumented endpoints on websites. 

Why Undocumented Endpoints Matter

Many ends are undocumented because they perform sensitive functions (admin tools, debugging tools, internal tools, legacy versions), thereby exposing data to potential unauthorized access. They are therefore highly important to not leave open/available to the public for an extended amount of time as they present opportunities for data leakage, bypassing authentication, or remote code execution.

Fast 5-Minute Workflow

Step 1: Passive Discovery (1-2 minutes), discover undocumented or forgotten endpoints by browsing the target website (as would be done by an ordinary user), while capturing traffic to and from the target website. Focus on discovering hidden endpoints within javascript files, as this is where most undocumented endpoints are found.

Tools Recommended:
1. Browser Devtools (Chrome/Firefox) Open the Network Tab and filter your request type for either “XHR” or “Fetch” to display API calls.

2. The Burp Suite Community (Free version) will allow for Proxy All Traffic Through Burp and then can be used with either Find Scripts or JS Miner Extensions to automate identifying endpoints in JavaScript files.

3. LinkFinder (Open Source) Python Script to extract Endpoints from JavaScript File.

An example of using the LinkFinder would be: 
python3 linkfinder.py -i https://target.com/main.js -o cli

Step 2: Extract and analyze the Target API for patterns including but limited to:
1. /api/v1/internal/
2. /admin/, /debug/, /test/, /beta/
3. versioned Endpoints (/api/v2/) or (/api/v3/), 4)
4. unusual paths (/graphql /private /backup)

Step 3: Conduct active fuzzing/brute-forcing to find hidden or unlisted paths using a fast fuzzer with a good wordlist.
An excellent fast fuzzer is ffuf (written in Go and is extremely fast).

Below is an example of how you could set up your command in your terminal: 
ffuf -u https://target.com/FUZZ -w /path/to/api-wordlist.txt -mc 200,201,204,301,302 -ac -t 50

Additionally, the following wordlists are great for use in 2026:
1. httparchive_apiroutes
2. swagger-wordlist
3. the common API paths provided by SecLists 

Step 4: Pipe your results into Nuclei for a quick scan of the endpoints you discovered for vulnerabilities.

For example:  
nuclei -l discovered-endpoints.txt -t http/api/ -severity medium,high

This will allow you to discover issues like exposing .env files or debug modes, or missing authentication on an API endpoint

Top Modern Tools for Finding Undocumented Endpoints 

For rapid personal or small business usage, the combination of Browser DevTools + ffuf + Nuclei is the most effective and powerful free stack available.

Improving Outcomes with Practical Tips

1. Use a targeted wordlist to target APIs instead of a general wordlist from a directory.
2. Using '-mc' (Match status codes) and '-ac' (Automatically calibrate) with 'ffuf' allows you to filter out excess noise.
3. You should examine your Options requests associated with each of your endpoints that you located in the discovery process to see what methods can be used from those endpoints.  
4. You should verify whether each of your endpoints has multiple versions of itself (ex: /api/v1/ or  /api/v2/).  By not performing this step you could potentially find an undocumented and/or unsecure endpoint on older versions of those API endpoints.   
5. You should look through your javascript files as a lot of your hidden endpoints only exist in your minified javascript files.  
6. You should be conducting all of these tests in a controlled environment, meaning that you have a signed authorization to do so (ex: your own apps or hunting for vulnerabilities on your authorized testing limits).  

Potential Risks Associated with Undocumented Endpoints

If there are undocumented or unexposed endpoints, you could run into the following risks: 
1. Data Leakage (Customer PII, application config files, etc.) 
2. Unauthorized Login As Another User With Privileges Beyond What Is Allowed
3. Violations of regulations (GDPR, etc.)
4. Increased attack surface for your website or application

Conducting regular discovery of and inventory of all endpoints is an important part of maintaining effective website security and protecting your customer's data privacy.

Key Takeaways

1. Passive javascript analysis and fast fuzzing are good ways to find many undocumented endpoints in 5 minutes or less.
2. The winning combination for 2026 that will continue to be free: Burp Suite/DevTools → LinkFinder → ffuf → Nuclei.
3. The best results come from javascript files and common API path patterns.
4. Any previously-discovered hidden endpoints should be verified & secured; they should either be deleted, or have sufficient authentication and input validation to keep them secure.
5. You can continue to protect yourself from hidden endpoint risks by using an enterprise tool, such as Akto or Levo.ai, for continual shadow API discovery.

Developing a habit of quickly discovering endpoints will greatly reduce hidden risk within your web apps.