Free JSONL Viewer for Inspecting Fine-tuning Datasets
Melvin Vivas · X post · 2026-08-11 · Open on X
Topics: Fine-tuning & Model Customization, AI Dev Tools & Productivity · Level: beginner
Summary
The creator shares a free, open-source tool he built for viewing and editing .jsonl files. JSONL is the usual format for fine-tuning and training datasets. He built it because he couldn't find a decent viewer, and recommends it to anyone fine-tuning models.
Key points
- Fine-tuning and training datasets are usually stored as .jsonl (one JSON object per line).
- Good JSONL viewers are hard to find, so the creator built his own.
- donvito/jsonl-viewer lets you view and edit .jsonl files.
- The tool is free and on GitHub.
- Inspect and clean your dataset rows before you start training.
Resources mentioned
- donvito/jsonl-viewer · repo · github.com · free
Open-source tool for viewing and editing .jsonl files (fine-tuning datasets) and agent traces from Codex, Claude Code, Pi and Hermes.
Also in: jsonl-viewer: Live Traces for Codex Orchestrator and Subagents (Melvin Vivas on X · notes), See live Codex traces with the jsonl-viewer tool (Melvin Vivas on X · notes), Melvin Vivas's open-source AI tools, built with Codex (Melvin Vivas on X · notes), Analyzing Codex Traces with jsonl-viewer (Melvin Vivas on X · notes) and 12 more
Try this
- Use a JSONL viewer to inspect and edit your fine-tuning dataset before training.
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