How we checked in participants for GDG DevFest Sri Lanka 2022

Chamod Shehanka Perera
3 min readDec 29, 2022


GDG DevFest Sri Lanka 2022

Typically, event attendant register and check in using a simple (Google form + Excel sheet) OR a platform like Google Developer Groups has bevy platform but the issue is that big events such as GDG DevFest Sri Lanka and Google I/O Extended Sri Lanka receive large registrations, and owing to limited resources, not everyone is able to attend and even if we setup limited tickets in the Bevy platform, there is no method for a selection process; instead, event attendees receive confirmation emails on a first come, first served basis. As a result, we had to take matters into our own hands.

High Level Diagram

GDG DevFest Sri Lanka 2022 Attendee Self Check-in High level diagram

When a user presents his or her QR code to the webcam, the content of the QR code is captured and validated using Firebase Cloud Firestore, as illustrated in the diagram above. Then web app will display the response like below.

Self Check in with the QR Code on Action

We could have use the DevFest dashboard for attendee check-in, but we wanted to add a self-check-in solution (Came this idea 2 days before the event 😅). QR codes are popular in Sri Lanka due to the fuel crisis, so we adopted the same strategy. We emailed invitations with QR codes to chosen participants and this is how they self checked with the QR.

Self Attendee Check in | DevFest Sri Lanka 2022

Used Library

There are various libraries available for scanning QR codes, but it is difficult to find one that works for both iOS/macOS Safari and desktop browsers. I could only use the react-zxing library, which rescued me.


Then we practically measured the time take for participant to get checked-in and distribute swags and decided when should we start the attendee check-in. However, not everything went as planned… 🙉

That’s pretty much all I had to share…..



Chamod Shehanka Perera

Software Engineer | GitHub Field Expert | Golang Sri Lanka Lead | GDG Organizer | KCD Sri Lanka Organizer| Beginner Surfer