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# Tutorial: a TOML format extension

By the end of this tutorial you have `@acme/jx-toml`, a standalone npm package that teaches every Jx host (build, dev server, Studio, runtime) to treat `.toml` files as content, with **no changes to any core package**. It is the worked example from the extensions spec, built step by step. Plan on about half an hour.

**Prerequisites**: you have read [The anatomy of an extension](/docs/extending/extensions/anatomy) and [Formats](/docs/extending/extensions/formats), and you have a Jx site project to test against ([Your first project](/docs/start/first-project)).

## 1. Scaffold the package

Create a package with a `jx` field pointing at the manifest, and export the manifest and class descriptor alongside the code:

```json shiki
```

The `"jx"` field is how hosts find the manifest; the `exports` entries make the JSON files importable by path, which matters once the package is consumed from `node_modules`.

## 2. Write the manifest

`jx-extension.json` at the package root enumerates what the package provides (here, a single class):

```json shiki
```

The manifest is pure data: it names things, and behavior lives in the class descriptors it points to. The class key `Toml` becomes the `$prototype`-visible name in every project that enables the extension.

## 3. Declare the format class

`src/Toml.class.json` is an ordinary Jx class descriptor. Its top-level `format` block is the [admission block](/docs/extending/extensions/classes) that puts it into file-extension dispatch:

```json shiki
```

`documentKinds: ["content"]` admits `.toml` as a content-collection source only. It does not enter pages/components discovery the way the parser's Markdown format does.

Note

`$implementation`
 says 
`./toml.js`
 while the source file is 
`toml.ts`
, the TypeScript convention of importing by emitted name. The first-party classes do the same (
`Markdown.class.json`
 points at 
`./markdown.js`
); Bun resolves it to the 
`.ts`
 source.

## 4. Declare the constructor and runtime access

Next, the class's `$defs` describe its instance surface, the standard external-class contract of a `config`-taking constructor plus an instance `resolve()`:

```json shiki
```

This is what makes `{ "$prototype": "Toml", "src": "./x.toml" }` work as a state entry at runtime.

## 5. Declare the parse capability

[Capability methods](/docs/extending/extensions/capabilities) are static methods declared by well-known `role` values, alongside `resolve` in `$defs.methods`:

```json shiki
```

`timing` includes `"client"` because TOML parsing needs no filesystem. Declaring it lets Studio parse in-process instead of round-tripping through the dev server.

## 6. Declare the content capabilities

`discover` lists entry files for a content source; `load` parses one source into entries. Both are node-only, so `timing` stops at `"server"`:

```json shiki
```

## 7. Implement the statics

The spec leaves `src/toml.ts` to you, and so does this tutorial, because the contract is the interesting part. Per the [host introspection contract](/docs/extending/extensions/anatomy), hosts import `$implementation` and take the export named by the class `title`. So `toml.ts` must export a `Toml` object (or class) whose static methods carry the declared identifiers: `parse` turning TOML source into an object with any TOML library, `discover` globbing `.toml` files under the source directory, `load` reading one file into content entries, and instance `resolve()` for runtime state access.

If you later want Studio saves or export sidecars for your format, add a `serialize` capability the same way. The parser's `Markdown.class.json` declares one; this example, like the spec's, elides it.

## 8. Use it in a project

A project enables the extension with one line, then names the format on a content type:

```json shiki
```

(`@jxsuite/parser` stays in the list because the `content` section itself belongs to it; your package contributes only the format.)

Run `jx schema` to regenerate the project's entry schema documents. This extension ships no [schema fragment](/docs/extending/extensions/schema-composition) (it contributes no `project.json` section), but the generator still picks up the class, so `"format": "Toml"` validates in the regenerated format-name enum.

You should now see the whole surface light up: the content loader discovers and loads `.toml` entries through your class, `ContentCollection`/`ContentEntry` queries work unchanged, pages can declare `{ "$prototype": "Toml", "src": "./x.toml" }` state for runtime access, and Studio lists `.toml` files (add a `$studio` block to the descriptor to refine its icon and editing modes).

## What you built

One package, three JSON files, and one implementation module: a manifest naming a class, a descriptor whose `format` block and capability roles tell every host what the class can do, and statics the hosts invoke, with no host knowing anything TOML-specific.

## Next steps

- [Tutorial: a guestbook extension](/docs/extending/extensions/tutorial-guestbook): the same pattern extended to project sections, tables, and a server mount.
- [Formats](/docs/extending/extensions/formats): everything the `format` block can declare, including `exportTarget` and `remote`.
- [Content collections](/docs/framework/site/content-collections): the user-facing model your format now feeds.

✕

Start here[Overview](/docs/start/)Get started[Install Jx Studio](/docs/start/install/)[Your first project](/docs/start/first-project/)[A tour of Jx Studio](/docs/start/studio-tour/)Tutorials[Tutorial: interactive component](/docs/start/first-component/)[Tutorial: blog with collections](/docs/start/first-collection/)[Video tutorials](/docs/start/videos/)Coming from another tool[Coming from WordPress](/docs/start/coming-from-wordpress/)[Coming from Webflow or Framer](/docs/start/coming-from-webflow/)[Coming from Wix or Squarespace](/docs/start/coming-from-wix/)[Coming from Lovable or Builder.io](/docs/start/coming-from-ai-builders/)Studio[Overview](/docs/studio/)[The desktop app](/docs/studio/desktop/)The workspace[Overview](/docs/studio/interface/)[Welcome screen](/docs/studio/interface/welcome-screen/)[Editors and views](/docs/studio/interface/modes/)[The canvas](/docs/studio/interface/canvas/)[Documents and panes](/docs/studio/interface/tabs/)[Quick 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guestbook](/docs/extending/extensions/tutorial-guestbook/)[First-party extensions](/docs/extending/extensions/first-party/)Embedding[Overview](/docs/extending/embedding/)[Hosting the Studio assets](/docs/extending/embedding/hosting/)[Writing a platform adapter](/docs/extending/embedding/platform-adapter/)[The backend protocol](/docs/extending/embedding/backend-protocol/)[Dev server internals](/docs/extending/embedding/dev-server/)[Embedding the runtime in your app](/docs/extending/embedding/runtime-host/)[Writing assistant tools](/docs/extending/embedding/assistant-harness/)UI kit[The Jx UI kit](/docs/extending/ui-kit/)Reference[Protocol routes](/docs/extending/reference/studio-routes/)[Implementation status](/docs/extending/reference/implementation-status/)[Spec changelog](/docs/extending/reference/spec-changelog/)[Standards alignment](/docs/extending/reference/standards/)Contributing[Working in the monorepo](/docs/extending/contributing/monorepo/)[Contributing to these 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