If you’ve ever spent hours wrestling with webpack configuration just to get your project’s config files to load properly, you’re not alone. For years, most JavaScript and TypeScript teams defaulted to JSON for configuration—simple, easy to parse, but limited. TOML, the “Tom’s Obvious, Minimal Language,” changed that, offering a syntax that’s human-friendly, supports nested data structures, dates, and more. But until recently, getting webpack to process TOML files required jumping through hoops with custom loaders or workarounds. As a loader provider, we built our toml-loader specifically to solve that pain point, and today I’m walking you through how to use it step by step, no fancy tricks required. Loader
First, let’s cut through the noise: what exactly is a webpack loader, and why does toml-loader matter here? Webpack is a module bundler, right? It takes your project’s different files—JS, CSS, images, and yes, config files—and packages them into static assets the browser can use. By default, webpack only understands JavaScript and JSON. If you try to import a .toml file directly, you’ll get an error like “You may need an appropriate loader to handle this file type.” That’s where loaders come in: they act as transformers, converting non-JavaScript files into valid modules webpack can consume. TOML is great for config because it’s way easier to read than JSON for complex setups—no more nested curly braces everywhere, comments you can actually use, and support for things like arrays and datetimes natively. Our toml-loader simplifies integrating that workflow directly into your webpack pipeline, so you can start using TOML in your projects without rewriting your entire bundler config.
Now, let’s get to the practical stuff. The first step is installing the loader. This is a standard npm package, so you’ll pull it in just like any other webpack dependency. I always recommend installing it as a dev dependency, since it’s only used during development and build processes. Open up your terminal, navigate to your project root, and run:
npm install toml-loader –save-dev
Or if you prefer yarn, that works too:
yarn add toml-loader –dev
Easy enough, right? Before we dive into configuration, let’s make sure we have a test TOML file to work with. Let’s say you have a project that uses TOML for environment-specific configs, or maybe a feature flag setup. Create a file called config.toml in your project root, and add some sample content to test. Here’s a realistic example for a small web app:
Main app configuration
app_name = "My Awesome Project"
version = "1.2.0"
production = false
API settings
[api]
base_url = "https://dev-api.myawesomeproject.com"
timeout = 5000
features = ["user_profiles", "dark_mode", "notifications"]
Date of last config update
last_updated = 2024-03-15T12:00:00Z
This is a typical TOML file—clear, structured, with comments, nested data under the [api] table, arrays, and a datetime. Perfect for testing our loader.
Next up: configuring webpack to use toml-loader. This is where most people get tripped up, because webpack loaders need to be ordered correctly—they run from right to left (or bottom to top, depending on how you write them) in the rule. For toml-loader, the process is simple: first, webpack will use toml-loader to convert the .toml file into a JavaScript object, and then that object will be treated as a valid module you can import in your code.
Your webpack config file is usually named webpack.config.js, so open that up. We’re going to add a module.rules entry that tells webpack to apply toml-loader to all .toml files. Here’s a basic, working config:
module.exports = {
entry: ‘./src/index.js’,
output: {
filename: ‘bundle.js’,
path: __dirname + ‘/dist’,
},
module: {
rules: [
{
test: /.toml$/i,
use: ‘toml-loader’,
},
],
},
};
Wait, that’s it? Yeah, for basic use cases, that’s all you need. The test property uses a regular expression to match any file ending with .toml (the i flag makes it case-insensitive, just in case you have .TOML files somewhere). The use property tells webpack which loader to apply—here, it’s just our toml-loader, so webpack will handle that conversion automatically.
But let’s level this up a little, because most projects don’t just have one TOML file. What if you have environment-specific configs, like config.prod.toml and config.dev.toml? You can use webpack’s rule options to add conditions, or even use webpack’s DefinePlugin to swap config files based on the build environment. Another common use case is wanting to parse the TOML and export it as an ES module, which works out of the box with our loader, but you can also add options if you need to customize the output. For example, if you want the loader to return a JSON string instead of a JavaScript object (though that’s not common), you could write:
{
test: /.toml$/i,
use: [
{
loader: ‘toml-loader’,
options: {
type: ‘json’,
},
},
],
}
But honestly, the default is almost always what you want. The loader’s default behavior is to parse the TOML string into a plain JavaScript object, which is then exported as a module, so you can import it directly in your React, Vue, or vanilla JS code. Let’s test that. In your src/index.js file, add an import statement for your config.toml:
import config from ‘./config.toml’;
console.log(‘App Name:’, config.app_name);
console.log(‘API Base URL:’, config.api.base_url);
console.log(‘Enabled Features:’, config.api.features);
Now run your webpack build (npm run build, assuming you have a build script in your package.json), and check the output. You should see those values logged in the browser console when you run your bundled app. That’s the whole flow—webpack takes the .toml file, runs it through our loader, turns it into a JS object, and makes it available in your code.
Wait a second, though—what about common pitfalls I’ve seen teams run into when using toml-loader? Let’s talk about those, because as a loader provider, I’ve fielded a lot of questions about this. First, loader order: if you’re using multiple loaders, like babel-loader or css-loader along with toml-loader, make sure toml-loader is the last one in the use array, right? Because loaders execute from last to first. For example, if you were processing a TOML file that exports something you wanted to pass through another transformer, you’d arrange them like this:
use: [‘another-loader’, ‘toml-loader’]
No, wait—no, that’s reversed. Let me clarify: webpack runs loaders in the order they’re listed in the use array, from bottom to top. So if you have use: [ ‘a-loader’, ‘b-loader’ ], webpack will process the file first with b-loader, then with a-loader. So for toml-loader, you almost always want it to be the first (last in the array) so it converts the TOML before any other loaders touch it. That’s a common mix-up, so keep that in mind.
Another pitfall: typos in the test regex. If your test is missing the $ at the end, like /.toml/, it will match any file that has .toml anywhere in the name, like myconfig.toml.backup, which you probably don’t want. Adding the $ makes it match only files that end with .toml, which is what you want. Also, case sensitivity: the i flag is safe to include, since TOML file extensions are almost always lowercase, but it doesn’t hurt to have it.
What if you need to process TOML files from node_modules? Wait, no—you shouldn’t import TOML files from node_modules, but if for some reason you have a custom package that exports a TOML file, you’ll need to adjust your rule to exclude node_modules, like this:
{
test: /.toml$/i,
exclude: /node_modules/,
use: ‘toml-loader’,
}
That keeps webpack from processing any TOML files inside dependencies, which avoids conflicts.
Now, let’s talk about why our toml-loader is the right choice here, not just any random toml npm package. A lot of people confuse the toml npm parser with a webpack loader. The toml package just parses TOML strings into JS objects, but that doesn’t integrate with webpack’s module system. Our loader wraps that parser and handles all the webpack-specific bits: caching, error handling, module exporting, and compatibility with all webpack versions back to webpack 4, so you don’t have to worry about version mismatches. We also regularly test our loader with the latest TOML spec, so it supports all the latest features, like inline tables, multi-line strings, and the new datetime formats added in TOML 1.0.
Wait, let’s test a more advanced example to show how flexible this is. Suppose you want to import a TOML file and only use a specific section of it, or validate the config before it’s exported. Our loader also supports custom transform functions, if you need that. For example, if you want to validate that the API timeout is a number between 1000 and 30000, you can add a transform option in the loader config:
{
test: /.toml$/i,
use: [
{
loader: ‘toml-loader’,
options: {
transform: (parsedToml) => {
if (parsedToml.api.timeout < 1000 || parsedToml.api.timeout > 30000) {
throw new Error(Invalid API timeout: ${parsedToml.api.timeout}. Must be between 1000 and 30000.);
}
return parsedToml;
},
},
},
],
}
That’s a game-changer for larger projects, where config validation is non-negotiable. You can run any custom logic on the parsed TOML before it’s exported as a module, so you catch errors at build time instead of runtime.
Now, let’s address a common question: can I use toml-loader with webpack 5? Absolutely. We built our loader to be compatible with all modern webpack versions, including webpack 5’s asset modules, but we keep the core functionality simple so it works in legacy projects too. If you’re using webpack 5, you can even pair our loader with asset modules if you want to handle TOML files as assets instead of modules, but that’s an advanced use case. Most teams will stick with the standard module approach we outlined earlier.
I’ve seen so many teams waste time writing custom code to load TOML in webpack projects, or struggle with loaders that are unmaintained or broken. When we built our toml-loader, we did it because we were tired of seeing developers re-invent the wheel. We’ve spent months refining it, fixing edge cases, and supporting the community, so you can rely on it to work consistently across all your projects.
If you’re still having trouble getting set up, or you need custom features for your enterprise project, our team works with teams of all sizes to customize loaders for specific use cases—whether that’s adding support for encrypted TOML files, integrating with your internal config management system, or optimizing build times for large projects with hundreds of TOML files. We don’t just sell loaders; we partner with teams to make their build processes smoother, so you can focus on building your product instead of wrestling with bundler configurations.
If you’re ready to upgrade your webpack workflow with TOML and our toml-loader, or if you need a custom loader solution for your project, get in touch with our team today to discuss your needs and see how we can help.
Wheel Loader References
Webpack Contributors. webpack: Module Bundler.
Preston-Werner, T. TOML: Tom’s Obvious, Minimal Language.
toml-loader Maintainers. toml-loader: Webpack Loader for TOML Files.
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