Choosing the technical stack for a new side project or early-stage startup is often a paralyzing decision. You are balancing development speed against scalability, ease of use against vendor lock-in, and immediate costs against long-term maintenance.

Enter Convex.dev. In the crowded market of Backend-as-a-Service (BaaS) providers like Firebase and Supabase, Convex has carved out a distinct niche by promising to eliminate the "glue code" between your frontend and database. It claims to be the backend that feels like using local state.

But is it the silver bullet for your specific idea?

As much as we love Convex for its developer experience, no tool is perfect for every scenario. In this guide, we will provide a pragmatic, balanced framework to help you decide when to go all-in on Convex and when to consider alternatives.

What is Convex? (A Quick Recap)

Before we weigh the pros and cons, let’s briefly define what you get out of the box. Convex is a modern backend platform designed specifically for reactive applications.

Its core value proposition rests on four pillars:

Real-Time by Default: The database is reactive. You don't set up WebSockets; you just query data, and your UI updates automatically when that data changes.
End-to-End Type Safety: It is built for TypeScript. The types flow automatically from your database schema to your React hooks without manual generation steps.
ACID Compliance: Unlike many NoSQL solutions that trade consistency for speed, Convex provides strong consistency with serializable isolation.
Serverless Functions: You write backend logic (Queries, Mutations, and Actions) in simple TypeScript functions that run in a serverless environment close to your data.

When to USE Convex: The Sweet Spots

If you are building a side project or a startup MVP, your primary resource is time. Convex excels in scenarios where iteration speed and "flow state" are paramount.

1. Rapid Prototyping & MVPs

For early-stage startups, the goal is to validate a hypothesis as quickly as possible. Convex removes the need to configure databases, set up API endpoints, manage connection pools, or worry about ORMs.

You can go from a blank file to a persisting todo list in minutes. Because the client library handles caching and optimistic updates for you, your MVP feels polished and "snappy" without the engineering hours usually required to optimize frontend state management.

2. Real-Time & Collaborative Applications

This is where Convex is arguably unrivaled. If you are building:

A chat application (Slack clone)
A collaborative text editor or whiteboard
A multiplayer game
A live dashboard or ticketing system

Convex handles the synchronization complexity for you. In a traditional stack, you would need to manage WebSocket connections, handle reconnection logic, and manually invalidate React Query caches. With Convex, it just works.

// The frontend automatically re-renders whenever the 'messages' table changes.
const messages = useQuery(api.messages.list);

3. TypeScript-First Teams

If your team (or just you) loves TypeScript, the experience is magical. You define your schema in code, and your frontend hooks instantly know the shape of your data.

There is no context switching. You don't have to look up API docs or SQL schema definitions; your IDE's autocomplete tells you exactly what fields are available. This drastically reduces runtime errors and "undefined" bugs, which is a massive productivity booster for small teams.

4. Teams with Limited Backend/DevOps Expertise

"Full-stack" often means "frontend developer who can write a Node endpoint." If you are a frontend specialist building a solo project, Convex allows you to build a robust backend without needing to know how to configure Docker, manage database migrations, or set up a Redis cache.

Convex is "Serverless" in the truest sense—the infrastructure is completely abstracted away.

5. Budget-Conscious Projects with Scale Potential

For side projects, Convex offers a generous free tier that includes ample storage and function execution limits. It allows you to host a project indefinitely without paying a cent until you actually get traction.

For startups, the "Convex for Startups" program provides significant credits, mitigating the risk of costs spiking before your revenue does.

When NOT to Use Convex: The "Red Light" Scenarios

While Convex is powerful, it is an opinionated platform. There are specific architectural and business requirements where it might fight against you rather than help you.

1. Highly Complex Relational Data Models

Convex uses a document-relational model. It supports relationships (via ID references) and is much better than Firestore at handling relational data. However, it is not a SQL engine.

If your application relies heavily on:

Complex multi-table joins in a single query.
Ad-hoc analytical SQL queries (aggregating millions of rows).
Strict foreign key constraints enforced at the database level.

You might find yourself writing a lot of application-level logic to mimic what PostgreSQL does natively. In these cases, Supabase or a managed Postgres instance might be a better fit.

2. Deep Vendor Lock-in Aversion

Convex is open-source, and you can self-host it. However, the "magic" comes from their managed cloud platform.

If your project has a strict requirement for:

Zero vendor lock-in (running standard containers on any VPS).
Complete control over the database file system.
Using standard open protocols exclusively (like standard SQL over TCP).

You should be aware that moving off Convex requires writing migration scripts to export data and rewriting your backend logic, as Convex functions are specific to their platform.

3. Existing Backend Infrastructure

If your startup already has a mature backend—perhaps a Go microservice architecture or a Rails monolith—introducing Convex can split your data sources.

Convex works best as the primary backend. While you can sync data into it, trying to keep a legacy SQL database in perfect sync with Convex to get "real-time features" on the side can introduce significant architectural complexity.

4. Heavy Compute or Long-Running Processes

Convex Queries and Mutations are designed to be fast and lightweight (typically less than 100ms).

If your backend needs to perform:

Heavy video processing (FFmpeg).
Complex Machine Learning model inference.
Long-running web scraping jobs.

You cannot run these directly inside a standard Query or Mutation. You would need to use Convex Actions (which run in a Node environment) or offload this work to external services (like AWS Lambda) and update Convex via API. If your app is 90% heavy compute, a traditional serverless stack might be more direct.

5. Specialized Database Requirements

Convex is a general-purpose document store. It is not a specialized engine for:

Graph Data: If you need native graph traversals (like Neo4j).
Time-Series: If you are ingesting millions of sensor readings per second (like InfluxDB).
Geospatial: While you can do basic filtering, heavy GIS workloads (PostGIS style) are not native.

Key Considerations for the Decision

To wrap up, here is a quick decision matrix for your next project:

Conclusion

For side projects, Convex is almost a no-brainer. The speed at which you can ship a polished, real-time, type-safe application is unmatched. It removes the friction that often kills side projects before they even launch.

For startups, it is a strategic choice. If your product relies on collaboration, live updates, or you need to iterate on product features faster than competitors using traditional stacks, Convex gives you a significant velocity advantage. However, if your core IP involves complex data analysis or heavy proprietary compute, evaluate if the document model fits your long-term roadmap.

Ultimately, the best backend is the one that lets you ship your product. For many of us in the JavaScript/TypeScript ecosystem, Convex is currently the fastest way to get there.

Ready to give it a shot? Check out our guide on building a shared to-do list with Convex to experience the speed yourself.

When (and When Not) to Use Convex.dev – A Guide for Side Projects and Startups