Terms of Service
Please read these Terms of Service carefully before using prochess.online. By accessing or using the site, you agree to be bound by these terms. Last updated: July 2026.
1. Acceptance of Terms
By accessing or using prochess.online ("the Service"), you affirm that you are at least 13 years of age and are fully able and competent to enter into the terms, conditions, obligations, affirmations, representations, and warranties set forth in these Terms of Service.
If you do not agree to all the terms and conditions of this agreement, you may not access or use the Service.
2. Description of Service
prochess.online provides a free, browser-based chess game analysis tool. The Service allows users to import chess games in PGN format (either from external platforms or by direct input) and receive automated engine analysis powered by Stockfish 18, running client-side via WebAssembly.
The Service is provided "as is" and we reserve the right to modify, suspend, or discontinue any aspect of the Service at any time without prior notice.
3. User Conduct
You agree not to:
- Use the Service for any unlawful purpose or in violation of any applicable laws or regulations
- Attempt to disrupt, overload, or attack the Service or its infrastructure (including DDoS attacks, vulnerability scanning, or unauthorized access attempts)
- Use automated scripts, bots, or scrapers to extract data or abuse the Service beyond normal personal use
- Upload or input content that contains malware, viruses, or any code designed to disrupt or damage computer systems
- Attempt to reverse-engineer, decompile, or extract the source code of the Service beyond what is publicly available
4. Intellectual Property
The prochess.online website, its design, layout, logo, original code, and original content are protected by copyright and other intellectual property laws. You may not reproduce, distribute, or create derivative works from the Service without explicit written permission.
Stockfish 18 is an open-source chess engine licensed under the GNU General Public License v3 (GPLv3). chess.js and chessboard.js are used under their respective open-source licenses. The chess piece images are sourced from Wikimedia Commons under their respective free licenses.
Chess games (PGN data) you input or upload remain your property. Since all analysis is performed client-side, we do not claim any ownership, license, or interest in the games you analyze.
5. Disclaimer of Warranties
THE SERVICE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED.
Without limiting the foregoing, we explicitly disclaim any warranties of merchantability, fitness for a particular purpose, quiet enjoyment, or non-infringement. We make no warranty that:
- The Service will meet your specific requirements or expectations
- The Service will be uninterrupted, timely, secure, or error-free
- The results obtained from engine analysis will be accurate, reliable, or suitable for any particular purpose
- Any errors or defects in the Service will be corrected
Chess engine analysis is inherently imperfect. Stockfish 18, while extraordinarily strong, can and does produce incorrect evaluations â particularly in complex positions, at shallow search depths, or in positions outside its training distribution. Move classifications (Brilliant, Best, Inaccuracy, Mistake, Blunder) are automated heuristic judgments based on engine evaluation deltas and should not be treated as absolute truth.
6. Limitation of Liability
To the fullest extent permitted by applicable law, prochess.online and its operators shall not be liable for any indirect, incidental, special, consequential, or punitive damages â including but not limited to loss of profits, data, use, goodwill, or other intangible losses â arising from:
- Your use or inability to use the Service
- Any conduct or content of any third party on the Service
- Unauthorized access, use, or alteration of your transmissions or content
- Any reliance placed on engine analysis, move classifications, or accuracy scores
Our total liability for any claims under these terms shall not exceed the amount you paid us to use the Service (which is $0 â the Service is free).
7. Third-Party Links and Services
The Service may contain links to third-party websites (including Chess.com and Lichess.org) and use third-party libraries (Three.js, Google Fonts). We do not endorse or assume responsibility for the content, privacy policies, or practices of any third-party websites or services. Interactions with third-party services are governed by their respective terms.
8. Advertising
The Service is supported by advertising revenue. We display advertisements from third-party ad networks. These advertisements may be targeted based on anonymous browsing behavior (not personal information). You acknowledge that the Service displays advertisements and agree not to block them in a way that interferes with the functionality of the site.
9. Termination
We reserve the right to terminate or suspend access to the Service at our sole discretion, without prior notice, for conduct that we believe violates these Terms or is otherwise harmful to other users, us, or third parties â or for any other reason.
10. Changes to Terms
We may modify these Terms at any time. Material changes will be noted with an updated date at the top of this page. Your continued use of the Service after changes constitutes acceptance of the modified Terms. If you disagree with the changes, you must discontinue use of the Service.
11. Governing Law
These Terms shall be governed by and construed in accordance with applicable laws, without regard to conflict of law principles. Any disputes shall be resolved through good-faith negotiation before pursuing other remedies.
Contact
Questions about these Terms? Reach us at support@prochess.online or via our Contact page.