---
title: Check Worker Bundle Size With wrangler check startup
description: wrangler check startup graduated from alpha in v4.116 and now shows real bundle size and a startup CPU profile. Run on this site: 3.95 KiB, gzip 1.54 KiB.
date: 2026-08-06T00:00:00.000Z
category: dev-tools
tags: wrangler, cloudflare-workers, cli, performance
---

## Quick Answer

`wrangler check startup` graduated from alpha in `wrangler@4.116.0` and now reports your Worker's real bundle size and a local startup CPU profile, all from a single terminal command, no deploy required. Run it before a deploy that would otherwise only surface a bundle-bloat or slow-startup problem as a production cold-start regression or a dashboard warning after the fact.

## What it actually reports

The changelog entry, from `cloudflare/workers-sdk`'s `packages/wrangler/CHANGELOG.md`, [`wrangler@4.116.0`](https://github.com/cloudflare/workers-sdk/releases/tag/wrangler%404.116.0) (released 2026-07-30):

> "Graduate `wrangler check startup` from alpha and show bundle size"

Run directly against this site's own built Worker:

```bash title="wrangler check startup, run on this repo"
$ wrangler check startup

 ⛅️ wrangler 4.118.0
────────────────────
├ Building your Worker
│ Worker Built! 🎉
│
├ Analysing
│ Startup phase analysed
│
│ Bundle: 3.95 KiB / gzip: 1.54 KiB
│
│ Local startup profile:
│   Profile window: 153.0 ms
│   Sampled time: 76.2 ms
│   Active: 71.6 ms (including 0.0 ms garbage collection)
│   Idle: 4.6 ms
│   Samples: 3
│
│ CPU Profile has been written to worker-startup.cpuprofile.
```

Two real numbers come out of this: the actual bundle size (gzip and raw), and a sampled CPU profile of the Worker's startup phase, written to a `.cpuprofile` file that loads directly into Chrome DevTools' profiler or VS Code for a flamegraph view.

<Callout type="info" title="Local timing is not production timing">
  Wrangler's own output is direct about this: the CPU profile runs on your local
  machine, which has a different CPU than Cloudflare's runtime. Use it to see
  where time is spent during startup, not to predict the exact cold-start number
  a real deploy will show.
</Callout>

## Structural Comparison Matrix

| Operational Aspect                    | Before (alpha, pre-4.116.0)                                 | After (v4.116.0+)                     |
| :------------------------------------ | :---------------------------------------------------------- | :------------------------------------ |
| **Command availability**              | Behind alpha gating                                         | Generally available                   |
| **Bundle size reported**              | Not shown                                                   | Raw and gzip size, in the same output |
| **How you'd catch bloat before this** | Only after a deploy, via dashboard or cold-start complaints | Locally, before deploying at all      |

## Fix it: add this to your pre-deploy routine

```bash title="run before a deploy, not after a regression report"
npm run build
wrangler check startup
```

The `.cpuprofile` file it writes isn't meant to be committed. It's a local diagnostic artifact, so add it to `.gitignore` if your project doesn't already ignore Wrangler's build output:

```gitignore title=".gitignore"
worker-startup.cpuprofile
```

## Confirmed version

Reproduced directly against this site's own build, `wrangler@4.118.0`, tracing back to the labeled graduation in `wrangler@4.116.0` (released 2026-07-30). The bundle size and profile numbers above are this site's real Worker, not illustrative figures. Browse more posts like this in the [Dev Tools](/dev-tools) archive.