TOML

Use Bun’s built-in support for TOML files through both runtime APIs and bundler integration

In Bun, TOML is a first-class citizen alongside JSON, JSON5, and YAML. You can:

• Parse TOML strings with Bun.TOML.parse
• import & require TOML files as modules at runtime (including hot reloading & watch mode support)
• import & require TOML files in frontend apps via Bun’s bundler

---

Runtime API

Bun.TOML.parse()

Parse a TOML string into a JavaScript object.

import { TOML } from "bun";
const text = `
name = "my-app"
version = "1.0.0"
debug = true

[database]
host = "localhost"
port = 5432

[features]
tags = ["web", "api"]
`;

const data = TOML.parse(text);
console.log(data);
// {
//   name: "my-app",
//   version: "1.0.0",
//   debug: true,
//   database: { host: "localhost", port: 5432 },
//   features: { tags: ["web", "api"] }
// }

Supported TOML Features

Bun’s TOML parser supports the TOML v1.0 specification, including:

• Strings: basic ("...") and literal ('...'), including multi-line
• Integers: decimal, hex (0x), octal (0o), and binary (0b)
• Floats: including inf and nan
• Booleans: true and false
• Arrays: including mixed types and nested arrays
• Tables: standard ([table]) and inline ({ key = "value" })
• Array of tables: [[array]]
• Dotted keys: a.b.c = "value"
• Comments: using #

const data = Bun.TOML.parse(`
# Application config
title = "My App"

[owner]
name = "John Doe"

[database]
enabled = true
ports = [8000, 8001, 8002]
connection_max = 5000

[servers.alpha]
ip = "10.0.0.1"
role = "frontend"

[servers.beta]
ip = "10.0.0.2"
role = "backend"
`);

Error Handling

Bun.TOML.parse() throws if the TOML is invalid:

try {
  Bun.TOML.parse("invalid = = =");
} catch (error) {
  console.error("Failed to parse TOML:", error.message);
}

---

Module Import

ES Modules

You can import TOML files directly as ES modules. The TOML content is parsed and made available as both default and named exports:

config.toml

[database]
host = "localhost"
port = 5432
name = "myapp"

[redis]
host = "localhost"
port = 6379

[features]
auth = true
rateLimit = true
analytics = false

Default Import

app.ts

import config from "./config.toml";

console.log(config.database.host); // "localhost"
console.log(config.redis.port); // 6379

Named Imports

You can destructure top-level TOML tables as named imports:

app.ts

import { database, redis, features } from "./config.toml";

console.log(database.host); // "localhost"
console.log(redis.port); // 6379
console.log(features.auth); // true

Or combine both:

app.ts

import config, { database, features } from "./config.toml";

// Use the full config object
console.log(config);

// Or use specific parts
if (features.rateLimit) {
  setupRateLimiting(database);
}

Import Attributes

You can also use import attributes to load any file as TOML:

app.ts

import myConfig from "./my.config" with { type: "toml" };

CommonJS

TOML files can also be required in CommonJS:

app.ts

const config = require("./config.toml");
console.log(config.database.name); // "myapp"

// Destructuring also works
const { database, redis } = require("./config.toml");
console.log(database.port); // 5432

---

Hot Reloading with TOML

When you run your application with bun --hot, changes to TOML files are automatically detected and reloaded without restarting:

config.toml

[server]
port = 3000
host = "localhost"

[features]
debug = true
verbose = false

server.ts

import { server, features } from "./config.toml";

console.log(`Starting server on ${server.host}:${server.port}`);

Bun.serve({
  port: server.port,
  hostname: server.host,
  fetch(req) {
    if (features.verbose) {
      console.log(`${req.method} ${req.url}`);
    }
    return new Response("Hello World");
  },
});

Run with hot reloading:

terminal

bun --hot server.ts

Now when you modify config.toml, the changes are immediately reflected in your running application.

---

Bundler Integration

When you import TOML files and bundle with Bun, the TOML is parsed at build time and included as a JavaScript module:

terminal

bun build app.ts --outdir=dist

This means:

• Zero runtime TOML parsing overhead in production
• Smaller bundle sizes
• Tree-shaking support for unused properties (named imports)

Dynamic Imports

TOML files can be dynamically imported:

const config = await import("./config.toml");