Bun bunfig.toml

bunfig.toml

Configure Bun's behavior using its configuration file bunfig.toml

Bun's behavior can be configured using its configuration file, bunfig.toml.

In general, Bun relies on pre-existing configuration files like package.json and tsconfig.json to configure its behavior. bunfig.toml is only necessary for configuring Bun-specific things. This file is optional, and Bun will work out of the box without it.

Global vs. local

In general, it's recommended to add a bunfig.toml file to your project root, alongside your package.json.

To configure Bun globally, you can also create a .bunfig.toml file at one of the following paths:

• $HOME/.bunfig.toml
• $XDG_CONFIG_HOME/.bunfig.toml

If both a global and local bunfig are detected, the results are shallow-merged, with local overriding global. CLI flags will override bunfig setting where applicable.

Runtime

Bun's runtime behavior is configured using top-level fields in the bunfig.toml file.

preload

An array of scripts/plugins to execute before running a file or script.

# scripts to run before `bun run`-ing a file or script
# register plugins by adding them to this list
preload = ["./preload.ts"]

jsx

Configure how Bun handles JSX. You can also set these fields in the compilerOptions of your tsconfig.json, but they are supported here as well for non-TypeScript projects.

jsx = "react"
jsxFactory = "h"
jsxFragment = "Fragment"
jsxImportSource = "react"

Refer to the tsconfig docs for more information on these fields.

• jsx
• jsxFactory
• jsxFragment
• jsxImportSource

smol

Enable smol mode. This reduces memory usage at the cost of performance.

# Reduce memory usage at the cost of performance
smol = true

logLevel

Set the log level. This can be one of "debug", "warn", or "error".

logLevel = "debug" # "debug" | "warn" | "error"

define

The define field allows you to replace certain global identifiers with constant expressions. Bun will replace any usage of the identifier with the expression. The expression should be a JSON string.

[define]
# Replace any usage of "process.env.bagel" with the string `lox`.
# The values are parsed as JSON, except single-quoted strings are supported and `'undefined'` becomes `undefined` in JS.
# This will probably change in a future release to be just regular TOML instead. It is a holdover from the CLI argument parsing.
"process.env.bagel" = "'lox'"

loader

Configure how Bun maps file extensions to loaders. This is useful for loading files that aren't natively supported by Bun.

[loader]
# when a .bagel file is imported, treat it like a tsx file
".bagel" = "tsx"

Bun supports the following loaders:

• jsx
• js
• ts
• tsx
• css
• file
• json
• toml
• wasm
• napi
• base64
• dataurl
• text

telemetry

The telemetry field is used to enable/disable analytics. By default, telemetry is enabled. This is equivalent to the DO_NOT_TRACK environment variable.

Currently we do not collect telemetry and this setting is only used for enabling/disabling anonymous crash reports, but in the future we plan to collect information like which Bun APIs are used most or how long bun build takes.

telemetry = false

env

Configure automatic .env file loading. By default, Bun automatically loads .env files. To disable this behavior:

# Disable automatic .env file loading
env = false

You can also use object syntax with the file property:

[env]
file = false

This is useful in production environments or CI/CD pipelines where you want to rely solely on system environment variables.

Note: Explicitly provided environment files via --env-file will still be loaded even when default loading is disabled.

console

Configure console output behavior.

console.depth

Set the default depth for console.log() object inspection. Default 2.

[console]
depth = 3

This controls how deeply nested objects are displayed in console output. Higher values show more nested properties but may produce verbose output for complex objects. This setting can be overridden by the --console-depth CLI flag.

Test runner

The test runner is configured under the [test] section of your bunfig.toml.

[test]
# configuration goes here

test.root

The root directory to run tests from. Default ..

[test]
root = "./__tests__"

test.preload

Same as the top-level preload field, but only applies to bun test.

[test]
preload = ["./setup.ts"]

test.smol

Same as the top-level smol field, but only applies to bun test.

[test]
smol = true

test.coverage

Enables coverage reporting. Default false. Use --coverage to override.

[test]
coverage = false

test.coverageThreshold

To specify a coverage threshold. By default, no threshold is set. If your test suite does not meet or exceed this threshold, bun test will exit with a non-zero exit code to indicate the failure.

[test]

# to require 90% line-level and function-level coverage
coverageThreshold = 0.9

Different thresholds can be specified for line-wise, function-wise, and statement-wise coverage.

[test]
coverageThreshold = { line = 0.7, function = 0.8, statement = 0.9 }

test.coverageSkipTestFiles

Whether to skip test files when computing coverage statistics. Default false.

[test]
coverageSkipTestFiles = false

test.coveragePathIgnorePatterns

Exclude specific files or file patterns from coverage reports using glob patterns. Can be a single string pattern or an array of patterns.

[test]
# Single pattern
coveragePathIgnorePatterns = "**/*.spec.ts"

# Multiple patterns
coveragePathIgnorePatterns = [
  "**/*.spec.ts",
  "**/*.test.ts",
  "src/utils/**",
  "*.config.js"
]

test.coverageReporter

By default, coverage reports will be printed to the console. For persistent code coverage reports in CI environments and for other tools use lcov.

[test]
coverageReporter  = ["text", "lcov"]  # default ["text"]

test.coverageDir

Set path where coverage reports will be saved. Please notice, that it works only for persistent coverageReporter like lcov.

[test]
coverageDir = "path/to/somewhere"  # default "coverage"

test.randomize

Run tests in random order. Default false.

[test]
randomize = true

This helps catch bugs related to test interdependencies by running tests in a different order each time. When combined with seed, the random order becomes reproducible.

The --randomize CLI flag will override this setting when specified.

test.seed

Set the random seed for test randomization. This option requires randomize to be true.

[test]
randomize = true
seed = 2444615283

Using a seed makes the randomized test order reproducible across runs, which is useful for debugging flaky tests. When you encounter a test failure with randomization enabled, you can use the same seed to reproduce the exact test order.

The --seed CLI flag will override this setting when specified.

test.rerunEach

Re-run each test file a specified number of times. Default 0 (run once).

[test]
rerunEach = 3

This is useful for catching flaky tests or non-deterministic behavior. Each test file will be executed the specified number of times.

The --rerun-each CLI flag will override this setting when specified.

test.retry

Default retry count for all tests. Failed tests will be retried up to this many times. Per-test { retry: N } overrides this value. Default 0 (no retries).

[test]
retry = 3

The --retry CLI flag will override this setting when specified.

test.concurrentTestGlob

Specify a glob pattern to automatically run matching test files with concurrent test execution enabled. Test files matching this pattern will behave as if the --concurrent flag was passed, running all tests within those files concurrently.

[test]
concurrentTestGlob = "**/concurrent-*.test.ts"

This is useful for:

• Gradually migrating test suites to concurrent execution
• Running integration tests concurrently while keeping unit tests sequential
• Separating fast concurrent tests from tests that require sequential execution

The --concurrent CLI flag will override this setting when specified.

test.onlyFailures

When enabled, only failed tests are displayed in the output. This helps reduce noise in large test suites by hiding passing tests. Default false.

[test]

This is equivalent to using the --only-failures flag when running bun test.

test.reporter

Configure the test reporter settings.

test.reporter.dots

Enable the dots reporter, which displays a compact output showing a dot for each test. Default false.

[test.reporter]
dots = true

test.reporter.junit

Enable JUnit XML reporting and specify the output file path.

[test.reporter]
junit = "test-results.xml"

This generates a JUnit XML report that can be consumed by CI systems and other tools.

Package manager

Package management is a complex issue; to support a range of use cases, the behavior of bun install can be configured under the [install] section.

[install]
# configuration here

install.optional

Whether to install optional dependencies. Default true.

[install]
optional = true

install.dev

Whether to install development dependencies. Default true.

[install]
dev = true

install.peer

Whether to install peer dependencies. Default true.

[install]
peer = true

install.production

Whether bun install will run in "production mode". Default false.

In production mode, "devDependencies" are not installed. You can use --production in the CLI to override this setting.

[install]
production = false

install.exact

Whether to set an exact version in package.json. Default false.

By default Bun uses caret ranges; if the latest version of a package is 2.4.1, the version range in your package.json will be ^2.4.1. This indicates that any version from 2.4.1 up to (but not including) 3.0.0 is acceptable.

[install]
exact = false

install.saveTextLockfile

If false, generate a binary bun.lockb instead of a text-based bun.lock file when running bun install and no lockfile is present.

Default true (since Bun v1.2).

[install]
saveTextLockfile = false

install.auto

To configure Bun's package auto-install behavior. Default "auto" — when no node_modules folder is found, Bun will automatically install dependencies on the fly during execution.

[install]
auto = "auto"

Valid values are:

install.frozenLockfile

When true, bun install will not update bun.lock. Default false. If package.json and the existing bun.lock are not in agreement, this will error.

[install]
frozenLockfile = false

install.dryRun

Whether bun install will actually install dependencies. Default false. When true, it's equivalent to setting --dry-run on all bun install commands.

[install]
dryRun = false

install.globalDir

To configure the directory where Bun puts globally installed packages.

Environment variable: BUN_INSTALL_GLOBAL_DIR

[install]
# where `bun install --global` installs packages
globalDir = "~/.bun/install/global"

install.globalBinDir

To configure the directory where Bun installs globally installed binaries and CLIs.

Environment variable: BUN_INSTALL_BIN

[install]
# where globally-installed package bins are linked
globalBinDir = "~/.bun/bin"

install.registry

The default registry is https://registry.npmjs.org/. This can be globally configured in bunfig.toml:

[install]
# set default registry as a string
registry = "https://registry.npmjs.org"
# set a token
registry = { url = "https://registry.npmjs.org", token = "123456" }
# set a username/password
registry = "https://username:password@registry.npmjs.org"

install.linkWorkspacePackages

To configure how workspace packages are linked, use the install.linkWorkspacePackages option.

Whether to link workspace packages from the monorepo root to their respective node_modules directories. Default true.

[install]
linkWorkspacePackages = true

install.scopes

To configure a registry for a particular scope (e.g. @myorg/<package>) use install.scopes. You can reference environment variables with $variable notation.

[install.scopes]
# registry as string
myorg = "https://username:password@registry.myorg.com/"

# registry with username/password
# you can reference environment variables
myorg = { username = "myusername", password = "$npm_password", url = "https://registry.myorg.com/" }

# registry with token
myorg = { token = "$npm_token", url = "https://registry.myorg.com/" }

install.ca and install.cafile

To configure a CA certificate, use install.ca or install.cafile to specify a path to a CA certificate file.

[install]
# The CA certificate as a string
ca = "-----BEGIN CERTIFICATE-----\n...\n-----END CERTIFICATE-----"

# A path to a CA certificate file. The file can contain multiple certificates.
cafile = "path/to/cafile"

install.cache

To configure the cache behavior:

[install.cache]

# the directory to use for the cache
dir = "~/.bun/install/cache"

# when true, don't load from the global cache.
# Bun may still write to node_modules/.cache
disable = false

# when true, always resolve the latest versions from the registry
disableManifest = false

install.lockfile

To configure lockfile behavior, use the install.lockfile section.

Whether to generate a lockfile on bun install. Default true.

[install.lockfile]
save = true

Whether to generate a non-Bun lockfile alongside bun.lock. (A bun.lock will always be created.) Currently "yarn" is the only supported value.

[install.lockfile]
print = "yarn"

install.linker

Configure the linker strategy for installing dependencies. Defaults to "isolated" for new workspaces, "hoisted" for new single-package projects and existing projects (made pre-v1.3.2).

For complete documentation refer to Package manager > Isolated installs.

[install]
linker = "hoisted"

Valid values are:

[debug]
# When navigating to a blob: or src: link, open the file in your editor
# If not, it tries $EDITOR or $VISUAL
# If that still fails, it will try Visual Studio Code, then Sublime Text, then a few others
# This is used by Bun.openInEditor()
editor = "code"

# List of editors:
# - "subl", "sublime"
# - "vscode", "code"
# - "textmate", "mate"
# - "idea"
# - "webstorm"
# - "nvim", "neovim"
# - "vim","vi"
# - "emacs"

install.security.scanner

Configure a security scanner to scan packages for vulnerabilities before installation.

First, install a security scanner from npm:

bun add -d @acme/bun-security-scanner

Then configure it in your bunfig.toml:

[install.security]
scanner = "@acme/bun-security-scanner"

When a security scanner is configured:

• Auto-install is automatically disabled for security
• Packages are scanned before installation
• Installation is cancelled if fatal issues are found
• Security warnings are displayed during installation

Learn more about using and writing security scanners.

install.minimumReleaseAge

Configure a minimum age (in seconds) for npm package versions. Package versions published more recently than this threshold will be filtered out during installation. Default is null (disabled).

[install]
# Only install package versions published at least 3 days ago
minimumReleaseAge = 259200
# These packages will bypass the 3-day minimum age requirement
minimumReleaseAgeExcludes = ["@types/bun", "typescript"]

For more details see Minimum release age in the install documentation.

bun run

The bun run command can be configured under the [run] section. These apply to the bun run command and the bun command when running a file or executable or script.

Currently, bunfig.toml is only automatically loaded for bun run in a local project (it doesn't check for a global .bunfig.toml).

run.shell - use the system shell or Bun's shell

The shell to use when running package.json scripts via bun run or bun. On Windows, this defaults to "bun" and on other platforms it defaults to "system".

To always use the system shell instead of Bun's shell (default behavior unless Windows):

[run]
# default outside of Windows
shell = "system"

To always use Bun's shell instead of the system shell:

[run]
# default on Windows
shell = "bun"

run.bun - auto alias node to bun

When true, this prepends $PATH with a node symlink that points to the bun binary for all scripts or executables invoked by bun run or bun.

This means that if you have a script that runs node, it will actually run bun instead, without needing to change your script. This works recursively, so if your script runs another script that runs node, it will also run bun instead. This applies to shebangs as well, so if you have a script with a shebang that points to node, it will actually run bun instead.

By default, this is enabled if node is not already in your $PATH.

[run]
# equivalent to `bun --bun` for all `bun run` commands
bun = true

You can test this by running:

bun --bun which node # /path/to/bun
bun which node # /path/to/node

This option is equivalent to prefixing all bun run commands with --bun:

bun --bun run dev
bun --bun dev
bun run --bun dev

If set to false, this will disable the node symlink.

run.silent - suppress reporting the command being run

When true, suppresses the output of the command being run by bun run or bun.

[run]
silent = true

Without this option, the command being run will be printed to the console:

bun run dev
echo "Running \"dev\"..."

Running "dev"...

With this option, the command being run will not be printed to the console:

bun run dev

Running "dev"...

This is equivalent to passing --silent to all bun run commands:

bun --silent run dev
bun --silent dev
bun run --silent dev