ESP32 dongle blocks 537,000 ads for $5

What happened

Egyptian developer ZedAxis (M-Abozaid on GitHub) has published a project that turns an ESP32-C3 SuperMini board — costing just $5 — into a DNS ad-blocking filter. The open-source firmware stores a list of 537,000 ad and tracker domains using 40-bit FNV-1a hashing to compress the data into the chip's 4 MB flash memory. According to reported tests, the device consumes only 50 KB of RAM and responds to blocked queries in about 10 milliseconds.

The dongle acts as a secondary DNS server on the home network, complementing the primary one (a Raspberry Pi-based Pi-hole). When the Pi-hole reboots or is unavailable, the ESP32 takes over DNS resolution by blocking unwanted domains. According to Tom's Hardware, latency is approximately 10 ms, comparable to more expensive solutions. The source code is available on GitHub and is based on the Arduino framework for ESP32, making it easy to replicate.

Why it matters

This project demonstrates that hardware-level ad blocking can be extremely cheap and efficient. Until now, popular solutions like Pi-hole required a Raspberry Pi (whose price has risen significantly due to semiconductor shortages) or a dedicated server. The ESP32-C3 costs less than $5 and consumes very little power, making it a viable alternative for budget-conscious users or for mass deployments in educational or low-power environments. Moreover, the 40-bit hashing technique is an ingenious innovation: it reduces the storage space needed for the domain list without generating too many collisions (false positives). With 32 bits, there would be many collisions; with 64 bits, space is wasted. The 40 bits offer an optimal balance for the 537,000 domains, achieving a collision rate below 1% according to the developer's calculations.

Historically, ad blocking has evolved from browser extensions (like AdBlock Plus in 2009) to network solutions like Pi-hole (2015). However, the latter required dedicated hardware costing at least $35 (Raspberry Pi Zero) or more. The ESP32-C3 dramatically lowers the entry barrier, opening the possibility for any home to have a hardware DNS filter for under $10. Additionally, its low power consumption (around 0.5 W) makes it ideal for 24/7 operation, with an annual electricity cost of less than $1.

Consequences and context

The rise of ad blockers has led to a constant war between publishers and users. Solutions like this empower users to regain control over their browsing, but they can also affect the revenue of websites that rely on advertising. However, ZedAxis's project is not the first in this space: alternatives like AdGuard Home (software) or Pi-hole already exist, but none are as cheap and compact. Using a microcontroller instead of a full computer reduces the carbon footprint and energy cost, aligning with sustainable computing trends. Furthermore, as a dedicated network device, it does not interfere with the performance of the main computer.

In comparison with past events, recall that in 2020, the Pi-hole project gained great popularity, but it required a Raspberry Pi that cost about $35 at the time. With inflation and chip shortages, Raspberry Pi prices have skyrocketed (an 8 GB Pi 4 costs over $100), making alternatives like the ESP32-C3 even more attractive. Moreover, the ESP32-C3 is a 32-bit RISC-V microcontroller with built-in Wi-Fi and Bluetooth, allowing future OTA updates if connectivity is added.

The impact on the ad-blocking market could be significant: if the community adopts this project, it could pressure router manufacturers to include built-in DNS filters, or even lead to low-cost commercial products. However, the project is still nascent and has not been independently tested at scale.

What readers should know

The project is available on GitHub (esp32-c3-adblock) and is open source. It requires basic electronics and programming knowledge to flash the firmware. Although the developer claims it works, no independent performance tests on real networks have been published. Users should consider that ad blocking may break some websites that rely on advertising scripts, and that using DNS over HTTPS (DoH) or DNS over TLS (DoT) can bypass the filter if not properly configured.

It is also important to note that the domain list is predefined and does not update automatically (though Wi-Fi connectivity could be added for updates). For most homes, a Pi-hole remains more flexible, but this dongle is an ultra-cheap and functional option. Advanced users can modify the firmware to include custom lists or periodic updates. Additionally, the ESP32-C3 SuperMini is easy to find online for less than $5, making it an accessible DIY project.

In summary, ZedAxis's project represents a milestone in democratizing hardware-level ad blocking, demonstrating that for under $10, an efficient DNS filter can be had. It remains to be seen whether the community adopts it and whether improved versions with automatic updates and greater customization appear.