## TL;DR
The RST writer walks the notebook through mistune, and an output node type it does not know (a newer widget output, a custom mimebundle) raises 'unknown node type'. Identify the cell whose output triggers it by converting with outputs stripped versus kept, then either clear that cell's outputs or pin a mistune version whose RST renderer knows the node. RST is a narrow format; rich outputs often do not survive it.

```text
nbconvert to rst failed with unknown node type error in mistune
```

## Use this when
- RST export fails with mistune complaining about an unknown node type.
- HTML export of the same notebook works.
- The notebook has widget or custom-mimetype outputs.

## Not for this skill when
- The export fails on templates. That is a template problem.
- RST generates but renders oddly. That is renderer fidelity.

## Steps
1. Bisect: export with `--clear-output` first. Verify: it succeeds, proving an output node is the trigger.
2. Re-add outputs in halves to find the offending cell. Verify: you can name the cell and its output type.
3. Clear or simplify that cell's outputs (replace widget output with a static figure). Verify: the export passes.
4. Alternatively, pin mistune to a version whose RST support covers your nodes. Verify: the export passes with outputs kept.
5. Re-run the full RST export. Verify: the .rst is written without node errors.

## Variant phrasings
### nbconvert rst unknown node type
Short form. An output node mistune cannot render.

### mistune error nbconvert rst
Library phrasing. Bisect the outputs.

### rst export failed jupyter
General phrasing. RST is narrow; simplify outputs.

Compatibility: nbconvert 6/7 with mistune 2/3. Node coverage differs by mistune version.

## Why it happens
RST is a much narrower format than HTML: it has no native concept of interactive widgets or arbitrary mimebundles. nbconvert's RST path leans on mistune's renderer, which only knows the node types its authors implemented. A notebook that is fine as HTML can contain output nodes that are simply unrepresentable in RST, and mistune reports that honestly as an unknown node.

## Edge cases / pitfalls
- Pinning mistune for one export can break other tools that need a newer mistune. Isolate the export env if needed.
- Stripping outputs loses information in the .rst. Prefer simplifying the output over deleting it.
- Custom mime types from extensions are the usual unknown nodes. Check what extensions the notebook uses.
- If RST is a hard requirement, design notebooks for it: static figures and text tables only.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_jibzfkjp9Ixktf4HX7dHkg