# Fastai

> fast.ai deep learning library. Use for practical deep learning.

- Skill: `majiayu000/fastai` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add majiayu000/fastai`
- Raw SKILL.md: https://api.skillmd.com/api/skills/majiayu000/fastai/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: majiayu000 (https://skillmd.com/u/majiayu000)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/majiayu000/fastai

---


# fastai

fastai is a layered API on top of PyTorch. It popularized **Transfer Learning** and good defaults (One Cycle Policy).

## When to Use

- **Learning DL**: The best course/library for beginners ("Practical Deep Learning for Coders").
- **Quick Baselines**: Get state-of-the-art results in 5 lines of code.

## Core Concepts

### Defaults

fastai chooses the best learning rate finder, optimizer (AdamW), and augmentations for you.

### Layered API

You can use the high-level `Learner` or peel back layers to raw PyTorch.

## Best Practices (2025)

**Do**:

- **Watch the Course**: Jeremy Howard's course updates annually and is world-class.
- **Use `nbdev`**: fastai's literate programming environment is powerful.

**Don't**:

- **Don't get stuck**: If you need something very custom, drop down to PyTorch.

## References

- [fast.ai](https://www.fast.ai/)