--- title: Clever hacker fits 537,000 domains in a tiny $5 ESP32... description: A developer built a DNS-based ad-blocker using a $5 ESP32-C3 microcontroller with only 400KB of RAM and 4MB of flash. The trick: instead of storing plaintext... canonical: https://daily.dev/posts/clever-hacker-fits-537-000-domains-in-a-tiny-5-esp32-ad-blocking-dongle-firmware-uses-only-around-4vxm5fukb twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Clever hacker fits 537,000 domains in a tiny $5 ESP32 ad-blocking dongle — firmware uses only around 50KB of RAM and can answer blocked lookups in 10 milliseconds | daily.dev og:description: A developer built a DNS-based ad-blocker using a $5 ESP32-C3 microcontroller with only 400KB of RAM and 4MB of flash. The trick: instead of storing plaintext... og:url: https://daily.dev/posts/clever-hacker-fits-537-000-domains-in-a-tiny-5-esp32-ad-blocking-dongle-firmware-uses-only-around-4vxm5fukb og:image: https://api.daily.dev/og/posts/4vXm5FuKb.png og:image:alt: Clever hacker fits 537,000 domains in a tiny $5 ESP32 ad-blocking dongle — firmware uses only around 50KB of RAM and can answer blocked lookups in 10 milliseconds og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Clever hacker fits 537,000 domains in a tiny $5 ESP32 ad-blocking dongle — firmware uses only around 50KB of RAM and can answer blocked lookups in 10 milliseconds **[Hacker News](https://daily.dev/sources/hn)** · 7 min read · 4 upvotes · 0 comments ## Summary A developer built a DNS-based ad-blocker using a $5 ESP32-C3 microcontroller with only 400KB of RAM and 4MB of flash. The trick: instead of storing plaintext domain names, the firmware downloads public blocklists, hashes each domain into a 40-bit FNV-1a value, sorts them, and writes the resulting table to flash. DNS queries are resolved via binary search against this hash table. The result fits 537,000 blocked domains (or ~250,000 with OTA update support retained) into 4MB of flash, uses only ~50KB of RAM at runtime, and answers blocked lookups in ~10ms. The device is designed as a low-power backup to a primary Pi-hole, powered passively from a router's USB port. ## Full article daily.dev links to this article rather than hosting it. 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