Backend model and developer surface
Convex is an integrated reactive backend where database queries and mutations are TypeScript functions. It provisions the database, generates typed APIs, runs server functions, tracks query dependencies, and pushes updated results to subscribed clients. Firebase is a wider Google platform that combines Firestore and Realtime Database with Authentication, Cloud Functions, Storage, Hosting, Analytics, Messaging, Crashlytics, and other mobile and web services. The first decision is therefore whether the team wants one strongly opinionated TypeScript data layer or a broad menu of independently adopted services.
Convex reduces architectural choice in exchange for cohesion: queries are deterministic, cached, and subscribable; mutations are transactions; actions call external services. Generated types connect the schema, server functions, and React client. Firebase gives teams more freedom to combine products, runtimes, and client SDKs, but the application must define how security rules, Cloud Functions, Firestore indexes, offline state, and event-driven workflows fit together. For a TypeScript product team starting a realtime application, Convex's narrower model removes more glue code than it removes useful flexibility.
Consistency, transactions, and data modeling
Convex describes its database as document-relational: JSON-like documents live in tables and can reference other documents by typed IDs. The database is ACID compliant, uses serializable isolation and optimistic concurrency control, and runs each mutation as a transaction. Queries read a consistent snapshot, and the client updates related subscriptions together so the interface does not briefly show mutually inconsistent states. This is a strong fit for collaborative tools, carts, multiplayer workflows, and operational dashboards where several views must move as one logical state change.
Cloud Firestore is a document database with transactions, batched writes, indexes, realtime listeners, and security rules, but its data model and billing encourage deliberate document boundaries. Cross-document access patterns require index planning, and listeners are billed when documents are added or updated. Firebase also offers Realtime Database with a different tree-shaped model and billing surface, creating another choice for teams. Firebase can support strict application logic, yet Convex makes transaction boundaries and reactive consistency part of the default programming model rather than a set of product-specific patterns the team assembles.
Realtime behavior and offline support
Convex automatically tracks every database dependency used by a query function. When underlying data changes, it invalidates the cached result, reruns the query, and pushes one consistent snapshot through the client connection. React's useQuery hook subscribes with a generated API reference and rerenders when the result changes; teams do not manually manage WebSocket topics or cache invalidation. Cached reads also avoid database-bandwidth charges in Convex's model. This makes realtime behavior an ordinary consequence of writing a query rather than a separate feature to wire up.
Firebase is the stronger offline-first platform. Firestore's mobile and web SDKs cache active data, allow reads and writes while disconnected, and synchronize local changes after connectivity returns; multiple changes to the same document resolve with last-write-wins behavior. Realtime listeners are mature across Android, Apple, and web, and Firebase's mobile SDK ecosystem covers far more than data synchronization. Convex can reconnect and restore subscriptions, but Firebase should win when offline operation, mobile platform integration, and Google's client tooling are primary requirements.
Type safety, server logic, and ecosystem
Convex generates api and data-model types from the application's functions and schema. TypeScript arguments, validators, document IDs, query results, mutation contexts, and React hooks stay connected end to end, giving editors and build tools visibility across the full request path. Server functions live beside the application code, and actions can call third-party APIs such as payment, messaging, or AI services. The model is especially productive for teams already committed to TypeScript and React because there is no separate ORM, SQL layer, or manually maintained REST schema.
Firebase supports JavaScript and TypeScript plus first-class Android, Apple, Flutter, Unity, C++, and other SDKs. Cloud Functions can run backend logic, while Google Cloud expands the ecosystem for queues, analytics, data warehousing, AI, and enterprise operations. That breadth is decisive for native mobile teams or organizations already standardized on Google Cloud. The trade-off is weaker end-to-end cohesion: Firestore documents, security rules, generated client types, functions, and analytics often rely on separate tools and conventions. Convex wins developer consistency; Firebase wins platform reach.
Pricing mechanics and cost predictability
Convex currently offers a Free and Starter path with included resources and pay-as-you-go overages, a Professional plan at $25 per developer per month, and Business or Enterprise options with a $2,500 monthly minimum. Published resource pricing separates function calls, database I/O, search query-GBs, and egress, with included allowances by plan. The dimensions are technical, but a team can map them to backend activity without counting every document returned to every listener. Automatic caching further reduces repeated backend work for identical reactive queries.
Firebase's Spark plan includes no-cost quotas, while Blaze is pay as you go. Cloud Firestore currently grants one free database per project with 1 GiB stored data, 50,000 document reads per day, 20,000 writes, 20,000 deletes, and 10 GiB monthly outbound transfer. Beyond that, charges include document and index-entry reads, writes, deletes, storage, and bandwidth. Realtime listeners can create a read charge whenever a result document changes or a disconnected client reestablishes the query. Firebase can be inexpensive at small scale, but read amplification makes cost forecasting workload-specific; Convex offers the clearer mental model for reactive applications.
Migration, lock-in, and operational posture
Convex owns more of the application backend, so migration means moving data, rewriting queries and mutations, replacing subscriptions, and recreating functions on another platform. Its open-source backend and support for SQLite, Postgres, and MySQL in the open-source version provide an escape path, but the managed developer experience remains a distinctive architecture. Teams should export data regularly, isolate external integrations behind actions, and understand which cloud features are portable before committing a core product.
Firebase lock-in appears across several services rather than one programming model: Firestore data shapes and security rules, Cloud Functions triggers, Authentication identities, Storage rules, Messaging, Analytics, and mobile SDK behavior can all become dependencies. Google Cloud provides mature governance and export tooling, but replacing a deeply integrated Firebase stack is still substantial. The right response is not to avoid every managed service; it is to choose the lock-in that buys the most leverage. Convex buys a coherent TypeScript backend, while Firebase buys a broad mobile and Google ecosystem.
Verdict: Convex wins for TypeScript-first realtime apps
Choose Firebase when offline-first mobile behavior, native Android or Apple support, Google Analytics and Messaging, or deep Google Cloud integration is central to the product. Its Spark quotas make prototyping accessible, and its client SDKs, security rules, and realtime databases have a long production history. Firebase is also the safer organizational choice when different teams need multiple languages and services rather than a single TypeScript backend model. Those strengths are real, but they bring more architecture and billing dimensions to coordinate.