JSONL Training File Validator
Paste a JSONL training file, find broken lines and message-role mistakes, then export the valid records.
Also useful for: jsonl validator fine-tuning jsonl validator openai jsonl validator JSONL Training File Validator
JSONL Training File Validator
Runs in your browser. Inputs are not uploaded.JSONL Training File Validator Example Run
Catch provider-blocking training rows before upload.
Sample inputs
{"messages":[{"role":"system","content":"Be concise."},{"role":"user","content":"Write a subject line."},{"role":"assistant","content":"Launch notes inside"}]}
{"messages":[{"role":"customer","content":"Bad role"}]}
{"prompt":"Product: rain jacket","completion":" Waterproof shell for wet commutes."}
{bad json}
Generated result
Summary: 2 valid records out of 4 non-empty lines. 2 errors, 1 warning.
Stats
- Records: 4
- Valid Records: 2
Issues
- Critical, line 2: Message 1 has unsupported role "customer".
- Critical, line 4: Line is not valid JSON. Expected property name or '}' in JSON at position 1 (line 1 column 2)
- Warning, line 2: Chat record has no assistant message.
Output
{"messages":[{"role":"system","content":"Be concise."},{"role":"user","content":"Write a subject line."},{"role":"assistant","content":"Launch notes inside"}]}
{"prompt":"Product: rain jacket","completion":" Waterproof shell for wet commutes."} What the JSONL Training File Validator Checks
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One JSON object per line
Every non-empty row is parsed independently, so one broken line does not hide the rest of the file.
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Chat message shape
The validator checks messages arrays, role values, and content fields expected by common chat fine-tuning formats.
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Prompt/completion fallback
Older completion-style records are accepted when both prompt and completion are strings.
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Clean export boundary
Rows with syntax or structural errors are left out of the downloadable clean JSONL output.
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Local privacy
Training examples, prompts, and uploaded text stay in the browser while the report is built.
JSONL Training File Validator Questions
- Q: Does the JSONL training file validator upload my training data? A: No. Inputs are processed in your browser, and pasted content is not sent to analytics or a server.
- Q: What should I paste into the JSONL training file validator? A: Paste JSONL with one training record per line. Chat-style records should contain a messages array; older records can use prompt and completion strings.
- Q: What can I copy or download? A: You can copy the issue report or download a clean JSONL file containing only rows without blocking errors.
- Q: What does the JSONL training file validator not verify? A: It does not judge answer quality, dataset balance, token limits, or whether a provider will keep the same fine-tuning rules forever.
Related Tools
Updates
- v1.0.0 New 2026-05-17: Added browser-side validation for chat and prompt/completion records.