Modern build stack

The modern build stack is two independent tracks. Enable either or both.

Meteor Bundler Optimizations (Meteor 3.3+). One flag, SWC replaces Babel, SWC minifier replaces Terser,
```
@parcel/watcher
```
replaces the legacy watcher, development skips legacy archs.
Rspack Bundler Integration (Meteor 3.4+). Atmosphere package delegates app-code compilation to Rspack. Tree shaking, ESM, code splitting via HTTP, modern bundler plugins.

Standard current

meteor create

application skeletons ship both enabled. Purposefully small or compatibility-oriented skeletons, including

minimal

and

legacy

, may omit Rspack or the modern flag. Inspect the generated

package.json

and

.meteor/packages

instead of inferring features only from the Meteor version. For existing apps, enable optimizations first, then add Rspack once the app code is standards-clean.

Enable Meteor Bundler Optimizations

Add to

package.json

json

"meteor": {
  "modern": true
}

This enables SWC, the SWC minifier, the modern watcher, and dev-mode web arch skipping. Each falls back to legacy when something is incompatible, so this is backward compatible.

Opt out of pieces:

json

"meteor": {
  "modern": {
    "transpiler": false,
    "minifier": false,
    "watcher": false,
    "webArchOnly": false
  }
}

Or scope SWC:

transpiler.excludeApp

transpiler.excludeNodeModules

transpiler.excludePackages

transpiler.excludeLegacy

. Accept

true

or an array of paths/regexes.

Verbose transpiler logs to diagnose Babel fallbacks:

json

"meteor": {
  "modern": {
    "transpiler": { "verbose": true }
  }
}

Look for

[Transpiler] Used Babel for <file> Fallback

. The common cause is nested imports; see

references/meteor-bundler-optimizations.md

Enable Rspack integration

bash

meteor add rspack

On first run the package installs the project-level Rspack setup. App code moves to Rspack; Meteor still handles Atmosphere packages and produces the final bundle. Requires entry points in

package.json

and no nested imports in app code. To migrate an existing app, use the

migrate-to-rspack

skill.

rspack

and

@meteorjs/rspack

follow the Meteor release, not the

@rspack/core

@rspack/cli

major. Meteor 3.4.0 uses both integration packages at v1. Meteor 3.4.1 and 3.5 use

rspack@1.1.0

with

@meteorjs/rspack@2.0.1

; Meteor 3.5.1 uses

rspack@1.2.0

with

@meteorjs/rspack@2.1.0

. Inspect

.meteor/versions

package.json

, and the lockfile. Run

meteor update --npm

after changing the Meteor release.

SWC config files

text

.swcrc > swc.config.js > swc.config.ts

Only the first found is used. Use

.swcrc

for static config,

swc.config.js

for environment-driven config. The file name must be exactly

.swcrc

, not

config.swcrc

Install

@swc/helpers

to externalize SWC helpers (smaller bundles):

bash

meteor npm install --save @swc/helpers

New apps ship with this preinstalled. Normally no further setup is needed; Meteor's pipeline detects it and emits imports instead of inlining. If only a production or legacy bundle fails on a helper import, inspect Rspack-generated and final Meteor output before changing

.swcrc

or adding manual imports.

Rspack config files

text

rspack.config.js | rspack.config.ts | rspack.config.mjs | rspack.config.cjs

Use

defineConfig

from

@meteorjs/rspack

. The function receives a

Meteor

parameter with build flags and helpers. See

references/rspack-config.md

for the full table and the most useful helpers (

extendSwcConfig

compileWithRspack

compileWithMeteor

extendConfig

splitVendorChunk

persistDevFiles

disablePlugins

enablePortableBuild

setCache

.meteorignore

Skip directories the bundler does not need to watch. Same syntax as

.gitignore

. Place at any depth; rules apply to the subtree.

gitignore

docs/
design/
cypress/
scripts/
*.md
!README.md

For per-command rules, set the

METEOR_IGNORE

env var.

Do not copy

.gitignore

into

.meteorignore

blindly. Exclude unrelated large trees that Meteor does not need, but never match the active Rspack build context: Meteor consumes its generated main and test modules during final assembly.

Rspack also generates

_build/

public/build-assets/

public/build-chunks/

, and

private/build-assets/

. Add those paths to the native ignore configuration of recursive formatters, linters, typecheckers, test discovery, coverage, and IDEs.

.gitignore

alone is insufficient.

Minifier ownership

"modern": true

selects Meteor's modern standard minifier. A third-party Atmosphere package that provides the JavaScript minifier remains part of the final Meteor assembly even when Rspack compiles app modules. Inventory custom minifier packages before migration. Keep or remove one only after comparing production output, source maps, build time, and runtime behavior.

Production legacy builds

Dev skips

web.browser.legacy

and

web.cordova

with

"modern": true

. Production still ships legacy by default. To drop legacy in production too, add

modern

.meteor/platforms

text

server
browser
modern

Memory limits

Rspack runs as a child process and may OOM on large apps. Raise the heap for tool processes temporarily when capturing evidence (Meteor 3.4.1+):

bash

TOOL_NODE_FLAGS="--max-old-space-size=16384" meteor run

On Meteor 3.4.0, use

NODE_OPTIONS="--max-old-space-size=16384"

First distinguish a one-shot build failure from growth during a long watch session. Audit large directories visible to Meteor and check the exact release for fixes. Test heap size and persistent cache as separate variables; revert a change that does not improve the failure or a measured memory trend.

Multiple instances

METEOR_LOCAL_DIR

isolates

_build

build-assets

build-chunks

bash

PORT=3000 METEOR_LOCAL_DIR=.meteor/local-1 meteor run
PORT=3001 METEOR_LOCAL_DIR=.meteor/local-2 meteor run

Anti-patterns

Enable optimizations and Rspack at the same time on a legacy app. Enable
```
"modern": true
```
first, clean up Babel fallbacks, then add Rspack.

Edit files inside

_build/

public/build-assets/

public/build-chunks/

, or

private/build-assets/

. Autogenerated.

Assume
```
.gitignore
```
prevents code-quality tools from scanning generated Rspack output. Configure each tool's own ignore mechanism.
Copy
```
.gitignore
```
to
```
.meteorignore
```
. Git may ignore Rspack's generated handoff even though Meteor must read it.
Remove a custom Atmosphere minifier only because Rspack is enabled. Benchmark the final production bundle first.
Disable Rspack persistent cache without need. It is the default and the main rebuild-speed win. Disable only when investigating OOM or a cache-related Rspack bug.
Name an SWC config
```
config.swcrc
```
or
```
rc.swc
```
. Only
```
.swcrc
```
is read.

meteor-modern-build-stack

NPX Install

Tags

SKILL.md Content

Modern build stack

Enable Meteor Bundler Optimizations

Enable Rspack integration

SWC config files

Rspack config files

.meteorignore

Minifier ownership

Production legacy builds

Memory limits

Multiple instances

Anti-patterns

See also