Open-Source JSONL Viewer for Fine-Tuning Datasets

Melvin Vivas · X post · 2026-06-27 · Open on X

Topics: Fine-tuning & Model Customization, AI Dev Tools & Productivity, Portfolio Projects · Level: beginner

Summary

The creator built an open-source viewer and editor for .jsonl files using GLM 5.2 in Cursor. Fine-tuning and training datasets for local LLMs usually come in JSONL format, and he couldn't find a good viewer, so he made one.

Key points

• Fine-tuning and training datasets are usually stored as .jsonl (one JSON object per line).
• donvito/jsonl-viewer lets you view and edit .jsonl files.
• It was built with GLM 5.2 inside Cursor, an example of using AI to build your own small tools.
• Checking your dataset by eye before fine-tuning a local LLM helps catch formatting errors.

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
• GLM 5.2 · tool · huggingface.co · free
  A GLM-family LLM (the transcript says 'GLM-5-2') that the demo ranked as a strong, affordable model for coding and design.
  Also in: Qwen3.8-Max on the Frontend Code Arena cost-performance frontier (Melvin Vivas on X · notes), Models That Work With the Hermes Agent for Personal Productivity (Melvin Vivas on X · notes), Open Model GLM 5.2 Helped Mitigate OpenAI-Caused Cyberattack (Melvin Vivas on X · notes), AI News Roundup: Claude Fable 5, Scientist AI, ZCode, NVIDIA RL (Melvin Vivas on X · notes) and 27 more
• Cursor · tool · x.com · free · recommended by both Bashiri Smith & Melvin Vivas
  AI-native code editor (VS Code with AI built in).
  Also in: GLM 5.3 and GLM 5.3 Flash now in Cursor (Melvin Vivas on X · notes), Grok Bot Can Now Hand Off Coding Tasks to Cursor (Melvin Vivas on X · notes), Why Plan Mode Still Matters in AI Coding Assistants (Codex, Claude, Cursor) (Melvin Vivas on X · notes), Why Plan Mode Still Matters in AI Coding Agents (Codex, Claude, Cursor) (Melvin Vivas on X · notes) and 121 more

Try this

• Use a JSONL viewer to inspect your training data before fine-tuning a local LLM.
• Build your own dev tool (like a JSONL dataset viewer/editor) with an AI coding assistant when existing tools fall short.