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In Bun, JSON5 is a first-class citizen alongside JSON, TOML, and YAML. You can:
  • Parse and stringify JSON5 with Bun.JSON5.parse and Bun.JSON5.stringify
  • import & require JSON5 files as modules at runtime (including hot reloading & watch mode support)
  • import & require JSON5 files in frontend apps with Bun’s bundler

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Conformance

Bun’s JSON5 parser is written in Rust and passes 100% of the official JSON5 test suite. The translated test suite lists every test case.

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Runtime API

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Bun.JSON5.parse()

Parse a JSON5 string into a JavaScript value. 
import { JSON5 } from "bun";

const data = JSON5.parse(`{
  // JSON5 supports comments
  name: 'my-app',
  version: '1.0.0',
  debug: true,

  // trailing commas are allowed
  tags: ['web', 'api',],
}`);

console.log(data);
// {
//   name: "my-app",
//   version: "1.0.0",
//   debug: true,
//   tags: ["web", "api"]
// }

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Supported JSON5 Features

JSON5 is a superset of JSON based on ECMAScript 5.1 syntax. It supports:
  • Comments: single-line (//) and multi-line (/* */)
  • Trailing commas: in objects and arrays
  • Unquoted keys: any valid ECMAScript 5.1 identifier
  • Single-quoted strings: in addition to double-quoted strings
  • Multi-line strings: using backslash line continuations
  • Hex numbers: 0xFF
  • Leading & trailing decimal points: .5 and 5.
  • Infinity and NaN: positive and negative
  • Explicit plus sign: +42
const data = JSON5.parse(`{
  // Unquoted keys
  unquoted: 'keys work',

  // Single and double quotes
  single: 'single-quoted',
  double: "double-quoted",

  // Trailing commas
  trailing: 'comma',

  // Special numbers
  hex: 0xDEADbeef,
  half: .5,
  to: Infinity,
  nan: NaN,

  // Multi-line strings
  multiline: 'line 1 \
line 2',
}`);

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Error Handling

Bun.JSON5.parse() throws a SyntaxError if the input is invalid JSON5: 
try {
  JSON5.parse("{invalid}");
} catch (error) {
  console.error("Failed to parse JSON5:", error.message);
}

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Bun.JSON5.stringify()

Stringify a JavaScript value to a JSON5 string. 
import { JSON5 } from "bun";

const str = JSON5.stringify({ name: "my-app", version: "1.0.0" });
console.log(str);
// {name:'my-app',version:'1.0.0'}

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Pretty Printing

Pass a space argument to format the output with indentation: 
const pretty = JSON5.stringify(
  {
    name: "my-app",
    debug: true,
    tags: ["web", "api"],
  },
  null,
  2,
);

console.log(pretty);
// {
//   name: 'my-app',
//   debug: true,
//   tags: [
//     'web',
//     'api',
//   ],
// }
The space argument can be a number (number of spaces) or a string (used as the indent character): 
// Tab indentation
JSON5.stringify(data, null, "\t");

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Special Values

Unlike JSON.stringify, JSON5.stringify preserves special numeric values: 
JSON5.stringify({ inf: Infinity, ninf: -Infinity, nan: NaN });
// {inf:Infinity,ninf:-Infinity,nan:NaN}

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Module Import

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ES Modules

You can import JSON5 files directly as ES modules:
config.json5
{
  // Database configuration
  database: {
    host: "localhost",
    port: 5432,
    name: "myapp",
  },

  features: {
    auth: true,
    rateLimit: true,
    analytics: false,
  },
}

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Default Import

https://mintcdn.com/bun-1dd33a4e/JUhaF6Mf68z_zHyy/icons/typescript.svg?fit=max&auto=format&n=JUhaF6Mf68z_zHyy&q=85&s=7ac549adaea8d5487d8fbd58cc3ea35bapp.ts
import config from "./config.json5";

console.log(config.database.host); // "localhost"
console.log(config.features.auth); // true

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Named Imports

You can destructure top-level properties as named imports:
https://mintcdn.com/bun-1dd33a4e/JUhaF6Mf68z_zHyy/icons/typescript.svg?fit=max&auto=format&n=JUhaF6Mf68z_zHyy&q=85&s=7ac549adaea8d5487d8fbd58cc3ea35bapp.ts
import { database, features } from "./config.json5";

console.log(database.host); // "localhost"
console.log(features.rateLimit); // true

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CommonJS

You can also require JSON5 files in CommonJS:
https://mintcdn.com/bun-1dd33a4e/JUhaF6Mf68z_zHyy/icons/typescript.svg?fit=max&auto=format&n=JUhaF6Mf68z_zHyy&q=85&s=7ac549adaea8d5487d8fbd58cc3ea35bapp.ts
const config = require("./config.json5");
console.log(config.database.name); // "myapp"

// Destructuring also works
const { database, features } = require("./config.json5");

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Hot Reloading with JSON5

When you run your application with bun --hot, Bun reloads JSON5 files when they change:
config.json5
{
  server: {
    port: 3000,
    host: "localhost",
  },
  features: {
    debug: true,
    verbose: false,
  },
}
https://mintcdn.com/bun-1dd33a4e/JUhaF6Mf68z_zHyy/icons/typescript.svg?fit=max&auto=format&n=JUhaF6Mf68z_zHyy&q=85&s=7ac549adaea8d5487d8fbd58cc3ea35bserver.ts
import { server, features } from "./config.json5";

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

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Bundler Integration

When you bundle with Bun, imported JSON5 files are parsed at build time and included as JavaScript modules:
terminal
bun build app.ts --outdir=dist
Parsing at build time means:
  • Zero runtime JSON5 parsing overhead in production
  • Smaller bundle sizes
  • Tree shaking of unused properties (named imports)

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Dynamic Imports

JSON5 files can be dynamically imported: 
const { default: config } = await import("./config.json5");