End User License Agreement

Last updated: April 10, 2026

This End User License Agreement ("Agreement") is a legal agreement between you ("You" or "Licensee") and Viaelo Corporation ("Viaelo," "we," "us," or "our"), located at 2108 N St, 8071, Sacramento, California 95816, United States.

This Agreement governs your use of Mermster ("Licensed Application"), a native desktop application for creating, editing, and exporting Mermaid diagrams, available for macOS and Windows.

By downloading, installing, or using the Licensed Application, you agree to be bound by the terms of this Agreement. If you do not agree, do not download, install, or use the Licensed Application.

1. License Grant

Viaelo grants you a limited, non-exclusive, non-transferable, revocable license to use the Licensed Application under one of the following tiers:

Free Tier

You may download, install, and use the Licensed Application at no cost on any number of devices. The free tier includes all features of the Licensed Application. Exports created with the free tier include a "Made with Mermster" watermark. The watermark is a feature of the free tier license, not a defect or limitation of the software.

Personal License

Upon purchase of a Personal license, you may install and activate the Licensed Application on up to five (5) devices that you own or control. The Personal license removes the watermark from exports and is intended for personal and freelance use only.

Commercial License

Upon purchase of a Commercial license, you may install and activate the Licensed Application on up to ten (10) devices within your organization. The Commercial license removes the watermark from exports and is required for business, commercial, or team use.

If you exceed the device limit for your license tier, you must purchase an additional license.

2. License Activation

Paid licenses require a one-time online activation using a license key and device identifier. After activation, the Licensed Application operates fully offline. The free tier does not require any network connection.

License keys are personal to you. You may not share, publish, or distribute your license key. Viaelo reserves the right to deactivate license keys that are shared or used in violation of this Agreement.

Your activated license is cached locally on your device using the operating system's secure keychain.

3. Updates

Your license entitles you to all updates to the Licensed Application at no additional cost. Updates may be governed by amended terms, which will be presented to you upon installation.

4. Restrictions

You may not:

  • Reverse engineer, decompile, disassemble, or attempt to derive the source code of the Licensed Application, except where expressly permitted by applicable law
  • Modify, adapt, translate, or create derivative works based on the Licensed Application
  • Redistribute, sublicense, rent, lease, lend, or transfer the Licensed Application or your license key to any third party
  • Remove, alter, or obscure any proprietary notices, labels, or marks on the Licensed Application
  • Use the Licensed Application in any manner that violates applicable law

5. Intellectual Property

The Licensed Application, including all code, graphics, user interface designs, and documentation, is the intellectual property of Viaelo Corporation and is protected by copyright, trademark, and other intellectual property laws. This Agreement does not grant you any ownership rights in the Licensed Application.

6. Privacy and Data Collection

Mermster is designed with privacy as a core principle:

  • Zero telemetry. The Licensed Application does not collect analytics, usage data, or behavioral information.
  • No account system. No registration or login is required.
  • One-time activation. The only network request made by a paid license is a one-time activation that transmits your license key and a device identifier. No other data is transmitted.
  • Local storage. Your diagrams, files, and preferences are stored locally on your device and are never transmitted to Viaelo or any third party.
  • License cache. Your activated license status is stored locally using your operating system's secure keychain.

For full details, see our Privacy Policy.

7. Payment Processing

Our order process is conducted by an authorized online reseller who acts as the Merchant of Record for all orders. The reseller handles payment processing, customer service inquiries related to billing, and returns.

For refund requests, see our Refund Policy.

8. Disclaimer of Warranties

THE LICENSED APPLICATION IS PROVIDED "AS IS" AND "AS AVAILABLE" WITHOUT WARRANTIES OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT.

Viaelo does not warrant that the Licensed Application will be error-free, uninterrupted, or free of harmful components. Viaelo warrants that the Licensed Application is free of spyware, trojan horses, viruses, or any other malware at the time of download from official sources.

9. Limitation of Liability

TO THE MAXIMUM EXTENT PERMITTED BY APPLICABLE LAW, IN NO EVENT SHALL VIAELO BE LIABLE FOR ANY INDIRECT, INCIDENTAL, SPECIAL, CONSEQUENTIAL, OR PUNITIVE DAMAGES, OR ANY LOSS OF PROFITS, DATA, OR GOODWILL, ARISING OUT OF OR IN CONNECTION WITH YOUR USE OF THE LICENSED APPLICATION.

VIAELO'S TOTAL LIABILITY UNDER THIS AGREEMENT SHALL NOT EXCEED THE AMOUNT YOU PAID FOR THE LICENSED APPLICATION IN THE TWELVE (12) MONTHS PRECEDING THE CLAIM.

10. Termination

This Agreement is effective until terminated. Your rights under this Agreement will terminate automatically without notice if you fail to comply with any of its terms. Upon termination, you must cease all use of the Licensed Application and destroy all copies in your possession.

Viaelo reserves the right to deactivate your license key if this Agreement is terminated due to a violation.

11. Governing Law

This Agreement shall be governed by and construed in accordance with the laws of the State of California, United States, without regard to its conflicts of law principles.

12. Changes to This Agreement

Viaelo reserves the right to modify this Agreement at any time. Changes will be posted at this page and will take effect upon posting. Your continued use of the Licensed Application after changes are posted constitutes acceptance of the modified Agreement.

13. Contact Information

For questions about this Agreement, contact:

Viaelo Support
2108 N St, 8071
Sacramento, CA 95816
United States
mermster@viaelo.app