Building Better Apps with Local-First Principles

Offline App Functionality
Data Privacy Solutions
CRDT Technology
Peer-to-Peer Apps
by Tiziano Perrucci
May 12, 2024

Rethinking App Architecture

For a long time, it has been a norm to build applications that rely heavily on cloud servers. Traditionally, these apps store user data in centralized cloud databases and require a constant internet connection to function effectively. The cloud-based model allows for real-time data syncing across devices and easy access from anywhere, which has driven its widespread adoption.

However, this approach comes with downsides, particularly in terms of privacy, data ownership, and dependence on continuous internet connectivity. Also, complexity of the system, with heavy back-end logic, increases development costs. As an answer to those challenges, the concept of Local-First software appeared. Local-First is a shift towards empowering users by keeping their data local to their devices as much as possible.

Local-First principles are related to apps that:

  • Operate fully offline, removing the reliance on an internet connection.

  • Store data primarily on the user's own devices, enhancing data privacy and security.

  • Sync changes between devices directly or through encrypted channels, maintaining user control and ownership.

This approach addresses privacy concerns and improves application responsiveness, as data access and manipulation are done locally. It also can decrease development costs. Further in this text, we'll dive deeper into the benefits of Local-First software, explore the technical challenges of implementing it, and discuss how it can transform app development to better meet user needs.

Local-First Principles

Local-First principles advocate for a fundamental shift in how applications manage and synchronize data, focusing on user empowerment by keeping their data close at hand – literally on their own devices.

Local-First software prioritizes:

Offline Functionality: Ensures that the application operates fully without an internet connection.

Local Data Storage: Keeps data on the user’s device, enhancing security and privacy.

Advanced Synchronization: Using both peer-to-peer syncing and sync-engines with declarative state changes to maintain data consistency across devices without central servers.

The diagram shows the major difference between the Local-First and Cloud-First systems: 

Local-First vs Could-First
Local-First vs Could-First

In the Local-First model, devices can sync directly or through a sync-engine that handles complex state changes and conflict resolution, supporting a more flexible and robust data flow.

We can see here several contrasts with Cloud-First strategies:

Data Privacy and Security: Local-First apps minimize data breaches by storing minimal data on central servers. Data remains primarily on the user's device, protected by local security measures.

User Ownership: Users maintain full control over their data. They can decide how data is shared and with whom, unlike in cloud-first scenarios where the server controls data access.

Offline Functionality: Local-First apps function seamlessly offline, accessing and modifying data without dependency on network connectivity. This feature is crucial in regions with unstable internet access or for mobile users on the go.

Simpler Backend: Local-First architectures generally require less complex backend systems. This reduction in backend complexity can significantly lower development and maintenance efforts, enabling smaller teams to manage and update systems more effectively.

The inclusion of sync-engines with declarative state changes, as discussed in Jim Nielsen’s blog on sync-engines, provides an additional layer of flexibility and power to Local-First architectures, enabling them to handle complex synchronization scenarios efficiently.

Technical Implementation

Implementing Local-First applications involves a set of technologies and architectural strategies. Understanding these technologies and the challenges associated with synchronization is crucial for developers looking to adopt this approach.

Technologies and Architectures

Local-First architecture aims into managing data locally while ensuring it remains synchronized across devices when connectivity is available:

Embedded Databases: Local-First apps often use embedded databases like SQLite or Realm, which store data directly on the device, allowing full functionality without network access.

Service Workers: In web applications, service workers play a crucial role by caching app data and assets on local devices, enabling apps to load and function offline.

Peer-to-Peer Communication: Technologies such as WebRTC allow direct communication between devices without needing to relay data through a central server, facilitating real-time data syncing.

Synchronization Challenges and Solutions

Synchronization is one of the most challenging aspects of Local-First development, particularly ensuring data consistency across devices after offline changes:

Conflict Resolution: When two devices make concurrent changes to the same data while offline, conflicts may arise once they reconnect. Solutions like Operational Transformation (OT) and Conflict-free Replicated Data Types (CRDTs) help resolve these conflicts automatically.

Data Integrity: Ensuring data remains intact and secure during synchronization processes is paramount. Techniques such as end-to-end encryption during data transfers can safeguard data privacy.

Frameworks and Tools

Several frameworks and tools have been designed specifically to support the development of Local-First applications. Examples include:

Automerge: Automerge is a library designed to help build collaborative applications by making it easier to merge changes from different users seamlessly. It is built on the principles of CRDTs, which allow local changes to be combined without conflicts.

CRDTs: CRDTs are data structures that reconcile changes made offline with the global state without conflicts. They are fundamental in Local-First apps where multiple users edit the same data independently.

PouchDB/CouchDB: These databases are built with synchronization in mind, allowing changes to be synced between local and remote databases smoothly and efficiently.

Synchronization Engines: Tools like Automerge and Yjs serve as synchronization engines, enabling declarative state changes that facilitate the seamless merging of user data updates from different devices. These engines interpret and apply changes made offline once connectivity is restored, ensuring data consistency across a Local-First application.

The diagram below presents the Sync Architecture using CRDTs

Local First Synchronisation Using CRDT
Local First Synchronisation Using CRDT

This diagram illustrates how CRDTs on each device manage local changes and synchronize these changes across devices using a synchronization engine, ensuring consistency without central control.

Real-World Applications

The adoption of Local-First principles is gaining traction across various industries, providing significant benefits in user privacy, data integrity, and operational resilience. Here are examples and case studies of successful Local-First applications and how specific companies have implemented these principles in their software.

Trello (Offline Mode)

Trello, a popular project management tool, offers an offline mode that enables users to continue accessing and interacting with their boards without an internet connection. Changes made offline are synchronized once connectivity is restored.

Automerge-Based Collaboration Tools

Automerge, a library designed for Local-First applications, has been successfully integrated into several collaborative platforms. These tools allow multiple users to work on documents simultaneously, with changes merged and conflicts resolved seamlessly. This is especially beneficial in environments where teams are distributed and need to collaborate in real-time without continuous server connectivity. 


Obsidian is a markdown note-taking application that operates entirely on local files without requiring a central server. Users can manage their knowledge base using plain text files stored locally, which can be synced across devices using any file-syncing service.

Ledger (Financial Tracking App)

Ledger, a personal finance application, adopted Local-First principles to ensure that users could track their expenses and manage budgets without ever sending sensitive financial information to the cloud. The app uses CRDTs to sync data across devices, ensuring that users' financial data remains private and secure, and is accessible across all their devices. 

These examples illustrate how Local-First principles are not only theoretical but practically applicable. As more companies explore and adopt these principles, the range of applications and their sophistication is expected to grow.


While the benefits of adopting Local-First principles are clear, transitioning to this approach brings challenges that organizations need to manage carefully.

Performance Issues

One of the main hurdles in implementing Local-First architecture is managing data synchronization across devices. Keeping multiple local copies of data in sync without causing performance bottlenecks requires sophisticated algorithms and can introduce latency issues, especially with large datasets.

User Adoption

Another challenge is user adoption. Users accustomed to cloud-based services may need to adjust to the different behavior of Local-First applications, particularly in terms of how data is accessed and synchronized. There may be concerns over the perceived reliability and responsiveness of an application that primarily relies on local data storage.

Overcoming Challenges

Optimizing Performance:

To address performance issues, developers can use optimized synchronization algorithms like Differential Synchronization to manage data efficiently. It's also crucial to implement smart caching systems that minimize data transfer costs and reduce latency. Testing performance under various network conditions can help fine-tune the system before full deployment.

Enhancing User Experience:

To facilitate user adoption, it's essential to ensure that the transition to a Local-First model is seamless and transparent. User interfaces should clearly indicate the synchronization status and provide users with manual control options to manage data sync. Educating users about the benefits of Local-First, such as increased privacy and reliability during offline use, can also help mitigate resistance.

Providing Support and Documentation:

Comprehensive documentation and support will help both developers and users. For developers, detailed guides on the architecture and troubleshooting common issues with Local-First apps are invaluable. For users, FAQs and tutorials on navigating the app's Local-First features can enhance their comfort and trust in the system.

Future of Local-First Development

As technology evolves and data privacy becomes increasingly important, the trend towards Local-First applications will grow. These applications offer an alternative to traditional cloud-centric models, providing improved security, privacy, and user control. The integration of Local-First principles is particularly relevant in an era where data breaches and internet unreliability are common concerns.

Cloud services will likely continue to play a role in Local-First architectures, but their function may shift towards providing optional, value-added services rather than serving as the primary data storage and processing hubs. This balanced approach could offer the best of both worlds, leveraging the cloud for heavy computation while keeping sensitive data local.


Adopting Local-First principles represents a significant shift towards building more resilient, user-centric software applications. As discussed in "Local-First Software: You Own Your Data, in spite of the cloud", the advantages of such systems are clear: enhanced privacy, increased control over personal data, and improved application reliability.

For organizations and developers looking to explore or implement Local-First technologies, now is the perfect time to start. If you need guidance on how to begin or want to ensure that your Local-First system is optimally designed, consider reaching out to Squads. Our team has expertise in developing robust Local-First solutions tailored to meet your specific needs and goals.