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A metalsmith plugin for transforming source files' contents. Complements @metalsmith/layouts

metalsmith: core plugin npm: version ci: build code coverage license: MIT


  • renders source files' contents field with any existing or a custom Jstransformer templating engine
  • alters file extensions from transform.inputFormats to transform.outputFormat
  • can be used multiple times with different configs per metalsmith pipeline



npm install @metalsmith/in-place jstransformer-handlebars


yarn add @metalsmith/in-place jstransformer-handlebars

This plugin works with jstransformers but they should be installed separately. jstransformer-handlebars is just an example, you could use any transformer. To render markdown you could install jstransformer-marked. To render handlebars you would install jstransformer-handlebars. Other popular templating options include: Nunjucks, Twig, Pug, or EJS. See also this map to see which extensions map to which jstransformer.


Pass @metalsmith/in-place to metalsmith.use :

import inPlace from '@metalsmith/in-place'

// shorthand
metalsmith.use(inPlace({ transform: 'nunjucks' }))

// same as shorthand
    transform: jsTransformerNunjucks, // resolved
    extname: '.html',
    pattern: '**/*.{njk,nunjucks}*',
    engineOptions: {}

In the transformed file, you have access to { ...metalsmith.metadata(), ...fileMetadata }, so that the following build

metalsmith.metadata({ title: 'Default title', nodeVersion: process.version }).use(inPlace({ transform: 'handlebars' }))

for a file:

title: Article title
<h1>{{ title }}</h1>Node v{{ nodeVersion }}

would render <h1>Article title</h1>Node v16.20

Multiple transforms can be used to target different sets of files, or to reprocess the same files multiple times in the order they are metalsmith.use'd:

// this build will apply the marked transform to, the handlebars transform to index.hbs,
// and handlebars first, marked second to both,, and html-minifier to all (only in production)
  .env('NODE_ENV', process.env.NODE_ENV)
  .use(inPlace({ transform: 'handlebars', extname: null }))
  .use(inPlace({ transform: 'marked' }))

if (metalsmith.env('NODE_ENV') !== 'development') {
  metalsmith.use(inPlace({ transform: 'html-minifier' }))


In most cases, you will only need to specify the transform and engineOptions option.

  • transform (string|JsTransformer): required. Which transformer to use. The full name of the transformer, e.g. jstransformer-handlebars, its shorthand handlebars, a relative JS module path starting with ., e.g. ./my-transformer.js, whose default export is a jstransformer or an actual jstransformer: an object with name, inputFormats,outputFormat, and at least one of the render methods render, renderAsync, compile or compileAsync described in the jstransformer API docs
  • extname (string|false|null): optional. How to transform a file's extensions: ''|false|null to remove the last transform.inputFormat matching extension, .<ext> to force an extension rename.
  • engineOptions (Object<string, any>): optional. Pass options to the jstransformer that's rendering the files. The default is {}.
  • pattern (string|string[]): optional. Override default glob pattern matching **/*.<transform.inputFormats>*. Useful to limit the scope of the transform by path or glob to a subfolder, or to include files not matching transform.inputFormats.

Extension handling

By default in-place will apply smart default extension handling based on transform.inputFormats and transform.outputFormat. For example, any of the source files below processed through inPlace({ transform: 'handlebars' }) will yield index.html.

source output
src/index.hbs build/index.html
src/index.hbs.html build/index.html
src/index.html.hbs build/index.html

The example demonstrates that:

  • order of extensions doesn't matter, order of plugin execution does!: you can pick the final extension to match the most suitable editor syntax highlighting
  • a single in-place run only alters the rightmost extension matching transform.inputFormats
  • you may choose to include or omit the transform.outputFormat in the source file name (.html in this case).


Pass options to the jstransformer that's rendering your templates via engineOptions. The metalsmith.json:

  "source": "src",
  "destination": "build",
  "plugins": [
      "@metalsmith/in-place": {
        "transform": "ejs",
        "engineOptions": {
          "cache": false

..would pass { "cache": false } to jstransformer-ejs.

If you use Pug, make sure to pass engineOptions: { filename: true }. This will ensure the filename of each processed file is passed to the render method as expected by this engine.

Multiple transforms per file

Suppose a file tags.hbs that lists all the article tags used on your website

title: Tags
description: Browse articles by tag
<h1>{{ title }}</h1>
<p>{{ description }}</p>
{{#each tags}}
  <li><a href="/tags/{{ . }}">{{ . }}</a></li>

To reduce Handlebars noise, you could add metalsmith.use(inPlace({ transform: 'marked' }) to your build and change the filename to to generate markdown syntax with Handlebars!

title: Tags
description: Browse articles by tag

# {{ title }}

{{ description }}

{{#each tags}}
- [{{.}}](/tags/{{ . }})

More markdown here..

Caution: when using multiple templating transforms per file, make sure there is no conflicting syntax. For example markdown will transform blocks indented by 4 spaces to <pre> tags, and marked's smartypants can potentially garble the result.

Usage with @metalsmith/layouts

In most cases @metalsmith/in-place is intended to be used before @metalsmith/layouts. You can easily share engineOptions configs between both plugins:

import inPlace from '@metalsmith/in-place'
import layouts from '@metalsmith/layouts'

const engineOptions = {}
metalsmith // index.hbs.hbs
  .use(inPlace({ transform: 'handlebars', extname: '', engineOptions })) // -> index.hbs
  .use(layouts({ engineOptions })) // -> index.html

@metalsmith/layouts uses a similar mechanism targeting transform.inputFormats file extensions by default. The example requires files ending in .hbs.hbs extension, but if you don't like this, you can just have a single .hbs extension, and change the in-place invocation to inPlace({ engineOptions, transform, extname: '.hbs' }) for the same result.


To enable debug logs, set the DEBUG environment variable to @metalsmith/in-place*:

metalsmith.env('DEBUG', '@metalsmith/in-place*')

Alternatively you can set DEBUG to @metalsmith/* to debug all Metalsmith core plugins.