StepFun open-sources onPanda: token-level LLM annotation and inspection tool
teortaxesTex · x · 2026-09-23
StepFun open-sourced onPanda, the tool it uses internally for LLM data annotation and model inspection — born from diyerxx's two-year effort building a token-level visualization & control web app (mobile-friendly). Workflow: find an error, correct the token, let the model continue.
Data annotation
- 52% lower median annotation time vs. manual post-editing
- SFT + preference data in one workflow, high on-policy fidelity (ΔPPL <1% vs. the model's resampling baseline)
- Precise token-level supervision with paired positive/negative examples; agent-trajectory annotation across image, audio, and video
Model inspection & debugging
- Inspect token probabilities and top-k alternatives, steer decoding token by token
- Explore SVG generation, web development, and agent tasks directly in the browser
Online demo and paper linked in the post.
Related event: StepFun Open-Sources onPanda for Faster Alignment Data Labeling(3 posts)→
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