Svelte DevTools

Before diving into the technical details and inevitable frustrations covered in the following sections, let's start with what makes this tool worth your time despite its quirks.

If you're tired of debugging with 47 console.log statements scattered around your components like breadcrumbs, this extension will save your sanity. It's the official DevTools extension from the Svelte team, so at least it's not some random person's side project that gets abandoned. Similar to React DevTools or Vue DevTools, but actually designed for Svelte's unique approach to reactivity.

Install it, restart your browser (because of course you have to restart), and you get a "Svelte" tab in DevTools. Only shows up in dev mode though - production builds strip all the debug info because nobody wants their component internals exposed to the world.

What You Get

Left panel shows your component tree. Click any component to see props and state on the right. You can edit values directly - strings, numbers, booleans all work. Arrays and objects expand, which is nice until you accidentally click on a massive data structure and crash your browser tab.

Element inspector lets you click stuff on your page and jump to that component. Works great until you have a {#each} block with 500 items - then it just gives up and highlights random shit three components away. The element inspector once confidently selected a navigation menu when I clicked on a form button. Real helpful.

State editing happens instantly, which is both a blessing and a curse. Component not updating? Change a prop value and see if it's your reactivity logic or just broken code. This saved me 3 hours of console.log hell when I couldn't figure out why my form validation kept failing - turns out the parent component wasn't passing the updated prop down like I assumed. Would've taken forever to track down without seeing the actual state values. Much better than traditional debugging techniques or relying on console methods alone.

SvelteKit Just Works

Run npm run dev and it works. No config bullshit needed. Compatible with most Vite setups, which is a miracle considering how many ways Vite configs can break.

The catch: dev mode only. Your app needs dev: true in compiler options or you get nothing. Production builds strip all the debug info to keep bundle sizes reasonable.

Current Version and Compatibility Hell

Latest version is from early 2024. Works perfectly with Svelte 4.x. Svelte 5 support is "experimental" which means it'll work great in demos and break spectacularly when you need it most.

Requires newer Chrome or Firefox because they rewrote the whole thing for Manifest V3. If you're still using Chrome 85 from 2020, you're shit out of luck.

Maintained by ignatiusmb under the official Svelte org, so at least someone gives a damn about keeping it updated. The project follows semantic versioning and has proper release notes for each update.

Now that you know what this extension promises to do, let's explore the specific features and where they inevitably break down in real-world usage...

Component Tree

Left panel shows your component tree. Click arrows to expand, but prepare to wait if you have more than 100 components. Shows Svelte components, HTML elements, and conditional blocks like {#if} and {#each}. Similar to how React DevTools displays component hierarchies, but optimized for Svelte's compile-time approach. The tree structure follows SvelteKit's component organization patterns and supports nested routing.

Tree updates automatically when components mount/unmount, which is great until you have a deeply nested app and the whole tree collapses every time something changes. Better than hunting through 47 source files trying to remember where you put that one component though.

Sometimes the tree doesn't load at all. Usually means you have multiple Svelte versions conflicting, or some genius decided to customize the Vite config in creative ways. Run npm ls svelte to check for version conflicts - you'll probably find Svelte 3.x hiding in some old dependency. I wasted 4 hours debugging a "broken" component before realizing the DevTools was showing me cached state from a completely different browser session. Always refresh first, learn from my pain.

State Editing (When It Doesn't Crash)

Click any component to see its props and state. You can edit strings, numbers, booleans directly. Arrays and objects expand, unless they're massive and your browser decides to take a coffee break. This feature leverages Svelte's reactivity system and integrates with Svelte stores for state management debugging.

Actually works for:

• Component props (most of the time)
• State variables including reactive ones
• Store values if the component subscribes properly
• Most reactive statements, except when they don't

Completely shits the bed on:

• Complex objects with circular references (crashes the tab)
• Functions (obviously, what did you expect?)
• Custom stores with weird logic
• Reactive statements that depend on 5 different things
• Anything involving dates or complex data structures

Changes happen instantly, which is great for testing but terrifying when you accidentally set a critical prop to undefined and your entire UI disappears. Way better than hardcoding test values in your component and forgetting to remove them before pushing to prod.

Element Inspector (The Guessing Game)

Click the crosshair, then click stuff on your page. Supposedly jumps to that component in the tree. Works about 60% of the time. The element inspector once confidently highlighted a header component when I clicked on a footer button. Amazing precision.

Gets completely lost with:

• Dynamic content from {#each} blocks (just gives up)
• Complex conditional rendering (highlights random parent components)
• Third-party libraries that mess with DOM (good luck)
• Any component nested more than 3 levels deep

When it actually works, it's faster than manually clicking through a 200-component tree. When it doesn't work, you'll spend more time figuring out why it selected the wrong thing than just finding the component yourself.

Browser Requirements and Performance Hell

Newer Chrome or Firefox only. They rewrote it for Manifest V3 because apparently the old version was too easy to use. If you're stuck on an old browser, go back to console.log debugging like it's 2015.

Only works in dev mode. You need dev: true in compiler options or you get absolutely nothing:

// vite.config.js
export default {
  plugins: [svelte({
    compilerOptions: {
      dev: true // Forget this and waste 20 minutes wondering why nothing works
    }
  })]
}

If the Svelte tab doesn't show up (which happens more than it should):

1. You're probably not in dev mode (run npm run dev, not npm run build)
2. Refresh after installing (classic browser extension bullshit)
3. Restart browser (because tech solutions from 1995 still work)
4. Check your Vite config isn't fucked

Performance is decent until you hit 200+ components, then it turns into molasses. Uses about 50MB RAM when active - not horrible, but don't leave it running if you're already pushing the limits of your 8GB laptop with 73 Chrome tabs and Slack eating the rest of your memory. Takes about 3 seconds to load the component tree on a project with 150+ components, and RAM usage jumps from 30MB to 80MB when you expand a big component tree. Your laptop fan will let you know.

Compatibility (Your Mileage May Vary)

SvelteKit: Works with npm run dev (the one command that actually matters)

Vite + Svelte: Works with standard `@sveltejs/vite-plugin-svelte` setups. Custom configs? Roll the dice.

Svelte 4.x: Fully supported and stable

Svelte 5: "Experimental" support that works great until it doesn't. It's beta software debugging beta software. What could go wrong?

TypeScript: Doesn't give a shit. Extension looks at the compiled JS, so your fancy types don't matter here.

Ready to install this tool and join the debugging revolution? Buckle up for the installation process, where things can go wonderfully right or spectacularly wrong...

Chrome Installation (The Easy Way)

Go to the Chrome Web Store and click "Add to Chrome". Restart your browser because Chrome still can't figure out how to activate extensions without a restart in 2025. The extension follows Chrome's Manifest V3 standards and integrates with Chrome DevTools APIs. You can also find it in the Chrome Extensions documentation as an example of proper DevTools integration.

Current version is from 2024. Reviews are mixed but mostly positive, which for a dev tool means "works most of the time."

Firefox Manual Install (Welcome to Hell)

Firefox users get completely fucked over. The Svelte team doesn't publish to Mozilla's addon store because Mozilla's review process is a bureaucratic nightmare. Manual install required:

1. Download svelte-devtools.xpi from GitHub releases
2. Open Firefox → about:addons
3. Gear icon → "Install Add-on From File"
4. Select the .xpi file
5. Enable "Always Allow on localhost" in extension settings

Mozilla's addon review process takes 2-3 weeks minimum and they reject extensions for absolutely ridiculous reasons like "uses too much storage" for a 2MB extension. Google approves Chrome extensions in 2 hours. The Svelte team looked at Mozilla's 47-page requirements document and said "fuck this, manual install it is." You can read about Firefox extension policies and Mozilla's review process to understand why developers avoid it. Compare this to Chrome's streamlined process and Edge's addon store.

When Nothing Shows Up (The Most Common Problem)

Extension tab doesn't appear and you're wondering if you wasted 5 minutes of your life. You're probably not in dev mode, which means no debug info was compiled into your app.

For SvelteKit: Use npm run dev, not npm run build or npm run preview. This should be obvious but apparently it's not.

For custom Vite setups, check your vite.config.js isn't missing the magic flag:

import { defineConfig } from 'vite'
import { svelte } from '@sveltejs/vite-plugin-svelte'

export default defineConfig({
  plugins: [svelte({
    compilerOptions: {
      dev: true // Forget this = waste 30 minutes debugging why nothing works
    }
  })]
})

Other reasons it completely ignores you:

• Browser too old (upgrade from Chrome 78, it's 2025)
• Forgot to refresh after installing (classic)
• Corporate firewalls blocking extension communication (good luck with that)
• Ad blockers interfering (uBlock Origin specifically hates dev tools)

Component Tree Won't Load (The Fun Never Ends)

Tree fails to load and you're left staring at an empty panel wondering what you did wrong this time. Common causes that will ruin your day:

Multiple Svelte versions fucking everything up. Run npm ls svelte and you'll probably find 3 different versions installed because some genius dependency decided to pin Svelte 3.44.2. The extension gets confused and gives up.

Someone got creative with Vite configs. If you or a coworker modified the standard `@sveltejs/vite-plugin-svelte` setup, congrats, you might have broken it. There's a known issue with certain custom configs that nobody has time to fix. Check the Vite configuration guide and SvelteKit's Vite integration docs for proper setup patterns.

Extension conflicts because browser extensions are territorial. Try disabling other dev tools temporarily. React DevTools and Vue DevTools apparently can't play nice together.

Corporate firewall being helpful. IT department blocking extension communication to localhost because security. Check your network settings and then argue with IT about why you need this for 45 minutes.

Browser Requirements (Because Backwards Compatibility is Dead)

Newer Chrome or Firefox only. They rewrote the entire extension for Manifest V3 compliance, leaving everyone on older browsers in the dust.

Old browsers won't work. Upgrade to Chrome 88+ or Firefox 78+ or go back to console.log debugging like it's 2010.

Version Compatibility (AKA Compatibility Roulette)

Svelte 4.x: Everything works reliably. Stick with this.

Svelte 5: "Experimental" support that works perfectly in demos and crashes spectacularly when you actually need it. It's beta software trying to debug beta software. Good luck.

SvelteKit: Works with any version using Svelte 4+. SvelteKit 2.x is fine.

Extension auto-updates through browser store, which means you get to play "will this update break my workflow" every few weeks. Works on Windows, macOS, Linux. Build tool doesn't matter as long as you remember to set dev: true.

Even after following all these installation steps, things will inevitably go wrong at the worst possible moment. Here are the questions everyone ends up asking when their debugging session turns into a troubleshooting nightmare...