dxc4
Legal

Terms of Service

Last updated: October 2026

Agreement to Terms

dxc4.com (the "Service") is made and run by Field Bureau & Werkstatt ("we", "us"). By accessing and using the Service, you accept and agree to be bound by these Terms. If you do not agree to them, please do not use the Service.

Description of Service

dxc4.com is a web-based chess analysis tool that provides:

  • Chess position analysis using the Stockfish 19 engine
  • Game import from Chess.com and import and export as PGN
  • Opening detection and classification
  • Win probability visualization
  • Interactive game navigation tools
  • Checkmate puzzles and a collection of classic games

The Service is provided free of charge and operates entirely within your web browser.

Acceptable Use

You agree to use the Service only for lawful purposes and in accordance with these Terms. You agree NOT to:

  • Use the Service for any illegal or unauthorized purpose
  • Attempt to interfere with, compromise, or disrupt the Service
  • Use automated tools to excessively access or burden the Service
  • Copy, scrape, or republish the puzzles, other than as the Puzzles section below allows
  • Reverse engineer, decompile, or attempt to extract the source code of our own software, except as an open-source licence allows (see Third-Party Content)
  • Remove, alter, or obscure any proprietary notices or labels
  • Use the Service to transmit harmful or malicious content

Intellectual Property Rights

Our Content

The Service and its original content, features, and functionality, including its software, design, text and puzzles, are owned by Field Bureau & Werkstatt and are protected by copyright, database and other intellectual property laws. All rights not expressly granted in these Terms are reserved.

The Puzzles

Every checkmate puzzle on dxc4.com is an original work, composed and proven for the Service. The positions, solutions, titles, numbering, the puzzle of the day and the collection as a whole are our proprietary content. They are not published under an open licence.

You may solve the puzzles, link to any puzzle page, and show or discuss an individual puzzle with a link back to its page on dxc4.com. Without our written permission you may not:

  • Copy, download in bulk, or scrape the collection or a substantial part of it
  • Republish puzzles in another collection, book, app, website or course
  • Use the puzzles to build a dataset, including for training or evaluating machine-learning models

Third-Party Content

The Service incorporates open-source components:

  • The Stockfish 19 chess engine, under the GNU General Public License v3, compiled to WebAssembly by the Stockfish.js project. The licence text is served with the engine at /stockfish/COPYING.txt, and the source code is available from the Stockfish project.
  • Opening names from the Lichess chess-openings dataset
  • Various open-source JavaScript libraries

These components keep their own licences and attributions, and nothing in these Terms limits the rights those licences give you. The moves of the classic games are historical records; the descriptions around them are ours.

Your Content

Any chess games or analysis you create using the Service remain your property. We do not claim ownership of your games or analysis data.

Privacy and Data Protection

Your privacy is important to us. Please review our Privacy Policy, which also governs your use of the Service, to understand our practices.

  • Analysis is performed locally in your browser
  • We do not store or transmit your chess games
  • No personal information is required to use the Service
  • Usage data is collected through Google Analytics and Vercel Web Analytics, as the Privacy Policy describes

Disclaimers and Limitations

Service Availability

The Service is provided "as is" and "as available" without warranties of any kind. We do not guarantee that:

  • The Service will be uninterrupted or error-free
  • All analysis results will be accurate
  • The Service will meet your specific requirements
  • Any defects will be corrected

Chess Analysis Accuracy

While we use the Stockfish 19 engine (a leading chess engine), chess analysis is complex and:

  • Analysis depth and time limits may affect accuracy
  • No chess engine is perfect or infallible
  • Results should be considered as guidance, not absolute truth
  • Human judgment remains important in chess evaluation

Limitation of Liability

To the maximum extent permitted by applicable law, we shall not be liable for any indirect, incidental, special, consequential, or punitive damages, or any loss of profits or revenues, whether incurred directly or indirectly, or any loss of data, use, goodwill, or other intangible losses.

Termination

We may terminate or suspend access to our Service immediately, without prior notice or liability, for any reason whatsoever, including without limitation if you breach the Terms.

Upon termination, your right to use the Service will cease immediately. Since the Service operates in your browser without accounts, termination primarily means restriction of access to the website.

Changes to Terms

We reserve the right, at our sole discretion, to modify or replace these Terms at any time. If a revision is material, we will try to provide at least 30 days' notice prior to any new terms taking effect.

By continuing to access or use our Service after those revisions become effective, you agree to be bound by the revised terms.

Governing Law

These Terms shall be interpreted and governed by the laws of the jurisdiction where dxc4.com operates, without regard to conflict of law provisions.

Contact

Questions about these Terms, or requests to use the puzzles, go to Field Bureau & Werkstatt at fieldbw.com.

Acknowledgment

By using dxc4.com, you acknowledge that you have read these Terms of Service and agree to be bound by them.