Embed the Wit parser

Run the Wit pipeline inside your own program — parse a document, feed it your own data, get HTML back — with no CLI, no subprocess, and no config file. This is for developers.

Step 1 — Install

Add the three packages you need:

npm install @witlang/parser @witlang/runtime @witlang/render-html

Step 2 — Run the whole pipeline

The pipeline is parse, then loadExternalData (only if the document loads external data), then resolve, expand, and finally a renderer. Verified end to end:

import { parse } from &#39;@witlang/parser&#39;;
import { loadExternalData, resolve, expand } from &#39;@witlang/runtime&#39;;
import { renderHtml } from &#39;@witlang/render-html&#39;;

const src = `@load meta load@
@load sales load@

@h1 Release @meta.version h1@
Cut @meta.date.

@table |rows @sales|
`;

// Feed data through the same seam the CLI uses. A plain dictionary pairs each
// alias with an already-resolved value; keys must match the @load aliases.
const doc = loadExternalData(parse(src, &#39;report.wit&#39;), {
  meta:  { version: &#39;0.4.0&#39;, date: &#39;2026-07-05&#39; },
  sales: [{ site: &#39;Dunmore&#39;, lit: &#39;yes&#39; }, { site: &#39;Harbour&#39;, lit: &#39;no&#39; }],
});

const html = renderHtml(expand(resolve(doc)), { mode: &#39;document&#39;, title: &#39;Release&#39; });

Result.

html is a full page whose body contains <h1>Release 0.4.0</h1><p>Cut 2026-07-05.</p> and a table with the two sales rows — verified. Pass mode: 'fragment' for embedding, or supply css to override the inlined theme.

The data seam

A data source is either a plain dictionary or a loader function. The dictionary form is simplest; a function of the shape (req) => value — where req carries the alias, its arguments, and a source location — fetches lazily per alias.

Multi-file documents

If the source uses reference, pass resolve options with a rootPath and a synchronous fileReader that takes an absolute path and returns the file's text. A single-file document needs no options.

Pitfalls

No load line, no data. Without the matching @load line the dictionary key is never consulted, and the reference stays unresolved.
References need a root. Calling resolve on a document that uses reference without a rootPath throws — the resolver refuses to silently drop references.