Playwright CDP fails to connect to Lightpanda on Bun (WebSocket closes with 1006)

[rejantoverlani]

Summary

We’re trying to use Lightpanda with Playwright (CDP) to generate PDFs in our API, but the connection fails when running on Bun.

This is currently blocking us from using Lightpanda in production.

We only use Playwright in this project (no Puppeteer).

---

Setup

• Lightpanda: v1.2.0

• Playwright Core: v1.58.2

• Runtime: Bun 1.3.9

• Lightpanda started with:

  lightpanda serve --port 9222
  

---

What we’re doing

const browser = await chromium.connectOverCDP({
  endpointURL: "ws://127.0.0.1:9222/",
});

---

Error

This is the exact error we’re getting:

Failed to connect to Lightpanda CDP at ws://127.0.0.1:9222/: overCDP: WebSocket error: ws://127.0.0.1:9222/ 101 Switching Protocols

Call log:
 - <ws connecting> ws://127.0.0.1:9222/
 - <ws unexpected response> ws://127.0.0.1:9222/ 101 Switching Protocols
 - <ws error> ws://127.0.0.1:9222/ error WebSocket was closed before the connection was established
 - <ws connect error> ws://127.0.0.1:9222/ WebSocket was closed before the connection was established
 - <ws disconnected> ws://127.0.0.1:9222/ code=1006 reason=

From logs:

connection successfully upgraded
connection closed: error.ConnectionResetByPeer

---

Behavior

• Connection starts
• Server responds with 101 Switching Protocols
• Then connection immediately closes (code 1006)
• Playwright never establishes a session

---

Fails on Bun

If we build with:

bun build --target bun

• WebSocket fails immediately
• Same code, same Lightpanda instance

---

Context

• This is for a large project (exam platform)
• We generate PDFs at scale
• Frontend runs on Node
• API runs on Bun
• We want to use Lightpanda for performance reasons

Switching everything to Node just to make this work isn’t ideal for us.

---

Question

Is Playwright + Lightpanda expected to work on Bun?

Or is this a known limitation with CDP / WebSocket handling?

---

Related

• Bun WebSocket issue: Playwright connectOverCDP() not working oven-sh/bun#9911
• Lightpanda issue Playwright CDP connection fails with assertion error #363 (CDP / Playwright): Playwright CDP connection fails with assertion error #363

---

What we need

Just trying to understand:

• Is this expected to work?
• If not, is there a recommended setup for Playwright users?
• Any workaround we should try?

---

Happy to test anything or provide more logs if needed.

[krichprollsch]

Hello @rejantoverlani
Thanks for the issue.

Did you test your playwright script with bun and chrome? Does it work in this configuration?

We don't generally use bun for our tests, I will try.

We generate PDFs at scale

Do you want to use Lightpanda to generate pdf? If so, it wouldn't work. Lightpanda don't provide any graphical rendering, so it can't generate screenshots or PDFs.

[rejantoverlani]

Hello @krichprollsch

Yes, we do want to use Lightpanda to generate PDFs.

Right now we already have PDF generation working using Playwright with Chromium in headless mode (no UI). Everything is done through the Playwright API and we return the PDF as a base64 buffer. That part is solid and works well for us in production.

The main reason we’re trying to switch to Lightpanda is performance. At the moment, generating a PDF takes around ~40 seconds, which is pretty slow for our use case. We’re hoping Lightpanda can help us cut that time down significantly since it’s much lighter than Chromium.

So we’re not trying to change how we generate PDFs — we just want to swap out Chromium for Lightpanda and keep the same Playwright-based flow.

Right now the blocker is that we can’t get a stable CDP connection when running on Bun, so we can’t actually test this setup properly.

If this is a supported use case, we’d really like to make it work.

[rejantoverlani]

Hello again,

Just to flag this — connectOverCDP is effectively deprecated / discouraged in Playwright and not really the recommended way to connect anymore.

From what we’re seeing, it also doesn’t work reliably in our setup (Bun), so even if we get past this specific issue, it doesn’t feel like a stable long-term solution.

Right now it seems like CDP + connectOverCDP is the only way to use Lightpanda with Playwright.

What would you suggest as the proper way to integrate Lightpanda with Playwright going forward?

Is there any plan to support the standard Playwright connection flow instead of relying on CDP?

[krichprollsch]

Right now we already have PDF generation working using Playwright with Chromium in headless mode (no UI). Everything is done through the Playwright API and we return the PDF as a base64 buffer. That part is solid and works well for us in production.

I understand, but Chrome computes graphical rendering even in headless mode, the UI and the result is not displayed. That's why Chrome can take screenshot and generate PDF in headless too.
Graphical rendering is required for PDF generation and Lightpanda don't do that. So unfortunately, your use case will not work w/ Lightpanda.

Just to flag this — connectOverCDP is effectively deprecated / discouraged in Playwright and not really the recommended way to connect anymore.

Good point, overall your issue is valid, I will take a look at it to see the best way to fix it.

[kaelkaram1231-bit]

Thanks for the clarification—this helps a lot.

…

On Tue, Mar 31, 2026, 7:22 AM Pierre Tachoire ***@***.***> wrote: *krichprollsch* left a comment (lightpanda-io/browser#2019) <#2019 (comment)> Right now we already have PDF generation working using Playwright with Chromium in headless mode (no UI). Everything is done through the Playwright API and we return the PDF as a base64 buffer. That part is solid and works well for us in production. I understand, but Chrome computes graphical rendering even in headless mode, the UI and the result is not displayed. That's why Chrome can take screenshot and generate PDF in headless too. Graphical rendering is required for PDF generation and Lightpanda don't do that. So unfortunately, your use case will not work w/ Lightpanda. Just to flag this — connectOverCDP is effectively deprecated / discouraged in Playwright and not really the recommended way to connect anymore. Good point, overall your issue is valid, I will take a look at it to see the best way to fix it. — Reply to this email directly, view it on GitHub <#2019?email_source=notifications&email_token=CAYBAH3HRPARKARY3MZXVPT4TO2BLA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTIMJWGIZDKMZRGQYKM4TFMFZW63VKON2WE43DOJUWEZLEUVSXMZLOOSWGM33PORSXEX3DNRUWG2Y#issuecomment-4162253140>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/CAYBAH4FB6KLHA2PVN7AD7T4TO2BLAVCNFSM6AAAAACXCCZK76VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHM2DCNRSGI2TGMJUGA> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[krichprollsch]

ok I tried some of our scripts from https://github.com/lightpanda-io/demo/ using bun instead of node and they worked...

$ bun ../demo/puppeteer/cdp.js
.................................................................................
...................
total runs 100
total duration (ms) 1039
avg run duration (ms) 10
min run duration (ms) 7
max run duration (ms) 34

$ bun -v
1.3.11

[krichprollsch]

Oh but it blocks w/ Playwright 👀

[krichprollsch]

ok I have the exact same issue with Chrome... I guess it's a bun <=> playwright issue

[krichprollsch]

I seems a lot issues are open regarding that on bun repo: https://github.com/oven-sh/bun/issues?q=is%3Aissue%20state%3Aopen%20playwright

Closing for now then.