Code Debugger
Commercial use OK
380+ models
No watermark
No sign-up needed
Model:
+ GPT-5, Claude, Gemini
Paste the code that's broken, paste the error or describe what's wrong, and get a fixed version + a plain-English explanation of what caused it. Works on 16+ languages and accepts stack traces directly.
What was wrong + how to prevent it next time
Advanced options
Result
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Find and fix bugs in your code with AI.
How to Use Code Debugger
1
Enter your input
Type text, upload a file, or describe what you want. No account needed.
2
Click generate
Our AI processes your request in seconds using the best open-source models.
3
Download & share
Download, copy, or share your result. Free for personal and commercial use.
Use this tool via API
Automate this tool from your own code. OpenAI-compatible REST endpoint, Bearer-token auth, no extra SDK required. Token costs match the web interface.
curl -X POST https://api.free.ai/v1/chat/ \
-H "Authorization: Bearer sk-free-..." \
-H "Content-Type: application/json" \
-d '{"model": "qwen-coder", "messages": [{"role": "user", "content": "Write a Python function that reverses a string."}]}'Code Debugger — FAQ
Paste broken code + the error message (or a description of what's wrong) and get back a fixed version plus a plain-English root-cause walkthrough. Works on 16+ languages and understands stack traces directly.
Yes. Self-hosted Qwen 3 Coder is free under the daily pool (~100 tokens per fix). Premium Claude Sonnet 4 / GPT-5 cost more but handle long-context multi-hundred-line files. The live quote shows the exact cost before you submit.
Four sections: Root cause (what actually broke), The fix (code block), Why the fix works, Prevent next time. You can toggle a side-by-side diff view comparing your original to the fixed version.
No — the fixer also needs the source code. Paste code into the first box, then the stack trace (or symptom description) into the error box. The error message is optional but highly recommended — it's how the AI localizes the bug fast.
Runtime errors (crashes, exceptions), compile/syntax errors, logic bugs (runs OK but wrong output), edge cases (works on most inputs, fails on some), performance bottlenecks, concurrency/race conditions, and network/API/integration issues. Pick the bug type for the most targeted prompt.
Python, JavaScript, TypeScript, Java, C++, C#, Go, Rust, Ruby, PHP, Swift, Kotlin, Shell/Bash, SQL, HTML/CSS, and more. Leave the picker on Auto-detect and the model figures it out from syntax.
Copilot is inside your editor. Free.ai Debug is browser-based — paste and go, no install. Use Copilot for in-flow suggestions; use Free.ai Debug when you want a focused root-cause explanation you can share with a teammate or PR description.
Stack Overflow makes you search. Free.ai Debug reads YOUR code and YOUR error together, so the fix is specific to your context — not a closest-match from 2013. For well-known errors ("cannot read property X of undefined") both work; for weird ones, Free.ai wins.
Click "Show diff" on the fixed-code panel. You see your original with removed lines in red and the model's changes in green, line-by-line. Great for review before pasting back into your codebase.
Code + error are sent to the model, processed, and discarded. Not stored, not used for training. For maximum privacy pick Qwen 3 Coder (self-hosted on our GPUs — your code never leaves our servers).
Up to 10,000 characters (~150 lines) on the self-hosted path. Premium long-context Claude/GPT handle 200K+ characters — upgrade when you're debugging a full-file regression.
Yes — POST a chat completion to /v1/chat/ with a system prompt describing your bug type and the code + error as the user message. See /api/ for the full spec.
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