Sätteri

Sätteri is a Markdown and MDX processing pipeline with a Rust parser and AST layer, plus a JavaScript plugin layer.¹

It sits between the JavaScript Markdown ecosystem and the Rust Markdown ecosystem: JavaScript has the larger plugin ecosystem, Rust has faster parsers, and Sätteri tries to combine the useful parts of both.

• The parser and syntax trees live in Rust.
• Transforms are written in TypeScript or JavaScript.
• Markdown transforms run against MDAST.
• HTML transforms run against HAST.
• MDX uses a separate parser entry point with the same plugin model.
• Native binaries are available for common desktop/server platforms, with a WASI fallback for browser and edge runtimes.¹

Sätteri is not a faster unified thought its tree shapes are familiar if you know remark and rehype, but its plugin API is not compatible with existing remark/rehype plugins.¹

Plugins

A plugin is an object with a name and one or more visitors. defineMdastPlugin and defineHastPlugin wrap those objects for type inference before they are passed to markdownToHtml.²

MDAST visitors are keyed by Markdown node type. They receive the node and a context object used for mutations:

import { defineMdastPlugin, markdownToHtml } from "satteri";

const emojis = defineMdastPlugin({
  name: "emojis",
  text(node, ctx) {
    if (node.value.includes(":wave:")) {
      ctx.setProperty(node, "value", node.value.replaceAll(":wave:", "👋"));
    }
  },
});

const { html } = markdownToHtml("Hi :wave:", { mdastPlugins: [emojis] });

HAST visitors use a tag filter. That makes them a better fit for HTML-level work, such as adding attributes to external links.²

Mutation Context

Plugins mutate through context rather than by treating every node as ordinary JavaScript-owned data. The context supports common tree work: setting properties, reading text content, finding parents, finding sibling indexes, and inserting children.³

That matters for transforms that touch siblings. A “sectionize headings” transform, for example, needs to climb to the parent and rewrite the parent’s child list once. The Sätteri docs use a WeakSet for that pattern so the first heading under a parent performs the rewrite and later headings under the same parent do nothing.²

Options

CompileOptions is shared by markdownToHtml and mdxToJs. The important fields for plugins are mdastPlugins, hastPlugins, features, fileURL, and data.⁴

fileURL must be a URL, not a string. When supplied, plugins read it as ctx.fileURL, which makes path-aware transforms possible.⁴

data seeds a document-level data bag. The same object is passed through the compile and returned as result.data, so each compile should receive its own throwaway object rather than a shared mutable one.⁴

Terms

Uses

Sätteri looks useful for heading IDs, image URL rewriting, external link attributes, section grouping, metadata collection, and document-aware transforms.

It is a poor fit when the main requirement is reusing existing remark or rehype plugins unchanged. In that case, unified remains the simpler choice.

Questions

• How stable is Sätteri’s API across early releases?
• Which host frameworks expose all compile options directly?
• How expensive are JavaScript plugin crossings on large documents with many visited nodes?
• When is the Rust parser worth losing direct access to the existing unified plugin ecosystem?