Series
How Apps Work
Queues, rate limits, ticks and traffic colours: the system design behind the apps on your phone.
▶ Short
How Apps Work
WhatsApp Ticks Explained: One Grey, Two Grey, Two Blue, and Why Blue Doesn't Always Mean Read
One tick is the server, two is the phone, blue is the eyes. How delivery and read receipts travel, why two grey ticks can sit for days, and how to read without blue.
21 Nov 2026
▶ Short
How Apps Work
What Does "Rate Limited" Mean? (Twitter, Discord, APIs and the 429 Error Explained)
Rate limited means you sent requests faster than the service allows, so it refused some. What the 429 error is, how token buckets count, and why apps do it on purpose.
19 Nov 2026