Terms of Use

Last updated: 17 October 2026

By using BlunderLens you agree to these terms. BlunderLens is a Berawa Digital project. Berawa Digital is a trading name of Berawa Experience S.L. (Spain), which operates the service and collects payments through Stripe as the merchant shown at checkout. Contact: berawadigital@gmail.com.

The service

BlunderLens analyses public chess games with the Stockfish engine and gives training suggestions. Results are automated estimates for educational purposes, with no guarantee of rating improvement.

Not affiliated with Chess.com

BlunderLens is independent and is not affiliated with, endorsed by or sponsored by Chess.com. We only use publicly available data from the Chess.com public API.

Daily Training Plan

The paid plan costs US$7 per month, billed through Stripe and renewing monthly until cancelled. You can cancel anytime yourself in the subscription portal (log in with the email you paid with) or by emailing us; cancellation stops future charges and the portal also lets you update your card and download invoices. If you are not happy with your first month, email us within 14 days for a full refund. EU consumers keep all their statutory rights.

Fair use

Do not abuse the service (for example, automated mass requests).

Open-source software

BlunderLens runs Stockfish 17.1 in your browser, using the unmodified single-threaded WebAssembly build from stockfish.js 17.1.0 (files served at /engine/stockfish.js and /engine/stockfish.wasm). Stockfish and stockfish.js are free software licensed under the GNU General Public License v3 (gnu.org). You may redistribute and modify them under that licence; they come with no warranty.

Complete corresponding source code: stockfish.js at the exact 17.1 release commit (build scripts and WebAssembly port) and Stockfish 17.1 (tag sf_17.1). If either link stops working, email berawadigital@gmail.com and we will send you a copy of the source for at least three years, at no charge beyond the cost of delivery. The engine runs as a separate program in a web worker; the rest of BlunderLens is our own code. We also use chess.js (BSD-2-Clause).

Liability

The service is provided "as is". To the extent permitted by law, our liability is limited to the amount you paid in the last 3 months. Spanish law applies.