Convex vs MongoDB for Solo Developers

Quick Comparison

Convex Overview

Convex is a reactive backend platform that combines a document database, server functions, and realtime subscriptions into one cohesive system. You write your backend logic as Convex functions (queries, mutations, and actions), and the platform handles reactivity automatically. When data changes, every client subscribed to a query that depends on that data gets updated instantly.

For solo developers, Convex removes a huge amount of plumbing. You do not set up a database, write API routes, configure WebSockets, or manage cache invalidation. You define your schema, write functions, and the frontend stays in sync automatically.

The development experience is TypeScript-first. Your schema generates types that flow through your queries and mutations all the way to your React hooks. If a field name changes, your IDE tells you everywhere it breaks before you even run the code.

The free Starter tier includes 1 million function calls, 0.5 GB of database storage, 1 GB of file storage, 1 GB of database I/O, and 20 GB-hours of action compute per month, with pay-as-you-go overage if you cross any line. That is enough to build and launch a real product without paying anything.

MongoDB Overview

MongoDB is the most popular document database. You store data as JSON-like documents in collections, with no fixed schema required. This flexibility made MongoDB the go-to choice for prototyping and applications where the data model evolves rapidly.

MongoDB Atlas (the managed cloud version) has a free M0 tier with 0.5 GB of storage, room for up to 100 databases and 500 collections, a 10 GB in and 10 GB out data-transfer cap per rolling seven days, and a shared cluster that pauses after 30 days of inactivity. The managed service handles scaling and security, although the free M0 tier does not include automated backups. For solo developers who do not want to manage database infrastructure, Atlas is the standard choice. The current MongoDB server line is the 8.0 LTS, with the latest rapid release at 8.3.1.

The query language (MQL) is powerful but different from SQL. You chain operators and use aggregation pipelines for complex queries. The learning curve is manageable, but developers coming from SQL often find MongoDB's approach unfamiliar at first.

MongoDB's ecosystem is massive. Mongoose for Node.js, Motor for Python, official drivers for every major language, and a large community producing tutorials, courses, and Stack Overflow answers.

Head-to-Head Comparison

By the Numbers (2026)

Marketing copy ages fast, so here are the figures that actually matter, each checked on 2026-05-28.

Convex

• Latest client package: convex 1.39.1 on npm.
• npm weekly downloads: about 731K for the convex package.
• GitHub: the open-source get-convex/convex-backend sits at roughly 11.7K stars and is written in TypeScript and Rust.
• Free Starter tier: 1M function calls, 0.5 GB database storage, 1 GB file storage, 1 GB database I/O, 20 GB-hours of action compute, and 1 GB egress per month.
• Pro tier: $25 per developer per month, bumping included limits to 25M function calls, 50 GB database storage, 100 GB file storage, 50 GB database I/O, and 250 GB-hours of action compute.
• Overage on Pro: $2 per additional million function calls, $0.20 per additional GB of storage or I/O.
• Self-hosting has been open source since February 2025 under the FSL Apache 2.0 license, with the code converting to plain Apache 2.0 two years after each commit.

MongoDB

• Latest server: 8.3.1, released 2026-05-04. The current long-term-support line is 8.0 (released 2024-10-31), with the latest 8.0 patch at 8.0.21.
• Official Node.js driver: mongodb 7.2.0 on npm, with roughly 11.3M weekly downloads. The Mongoose ODM adds another 5.2M weekly downloads.
• GitHub: mongodb/mongo is around 28.3K stars and is written in C++.
• Atlas M0 free tier: 0.5 GB storage, up to 100 databases and 500 collections, 100 operations per second, 500 concurrent connections, and a 10 GB in and 10 GB out transfer cap per rolling seven days. No automated backups, and the cluster pauses after 30 days of inactivity.
• Flex clusters start at roughly $8 per month and scale toward $30, adding 2 GB to 5 GB of storage, backups, and API access. Dedicated clusters (M10 and up) start at roughly $57 per month.

The download and star gaps tell the honest story. MongoDB is a 2009-era incumbent with a driver pulling tens of millions of installs a week and an ecosystem nobody else can match. Convex is the younger, faster-moving platform whose adoption curve is real but an order of magnitude smaller.

Real Cost at Solo-Dev Scale

Sticker prices do not predict your bill. Here is a concrete worked example for a typical solo-launched app, using the real published rates.

Assume a small but live product: a few hundred daily active users generating about 5 million Convex function calls a month, 2 GB of database storage, and modest file storage well under the included allowance.

On Convex, the free Starter tier caps at 1M function calls and 0.5 GB of database storage, so this workload is past the free line. Moving to Pro costs $25 per developer per month, and that single tier already includes 25M function calls and 50 GB of database storage, so the 5M calls and 2 GB sit comfortably inside the bundle with no overage. Your bill is a flat $25 per month as a solo developer, and it stays $25 until you cross 25M calls or 50 GB.

On MongoDB Atlas, the equivalent workload outgrows the M0 free tier on storage and operations the moment it is genuinely live, since M0 throttles at 100 operations per second and gives no backups. The realistic next step is a Flex cluster (roughly $8 to $30 per month depending on usage) or, once you want backups and predictable performance, a dedicated M10 at roughly $57 per month before backup storage and egress. Self-hosting the Community Edition on a small VPS can be cheaper in raw dollars, but you then own backups, upgrades, monitoring, and security patching yourself.

The honest read for a solo developer: at this small-but-real scale, Convex's flat $25 buys you the database plus the entire backend layer (functions, realtime, auth integration), while MongoDB's $8 to $57 buys you only the database, and you still write the API, the realtime layer, and the auth around it. If your app is a React product that needs realtime, Convex's single number is doing far more work. If you already have a backend in another language and just need durable document storage, MongoDB's cheaper Flex tier wins on raw cost.

When to Pick Convex

Pick Convex when you are building a realtime application and you want reactivity without the work. Collaborative tools, live dashboards, chat applications, multiplayer features: anything where multiple users need to see the same data update simultaneously is where Convex shines.

It is the right choice when you want to skip building a backend entirely. Convex functions replace your API layer. You write a query function, call it from React, and it stays reactive. No Express server, no REST endpoints, no GraphQL schema, no WebSocket setup.

Choose Convex if you are a React developer who wants the fastest path from idea to working product. The integration with React (and Next.js) is excellent. The development loop of writing a function and immediately using it in your component is hard to beat for speed.

When to Pick MongoDB

Pick MongoDB when you need a general-purpose document database with maximum flexibility. MongoDB works with any backend framework, any language, and any deployment model. You are not locked into a specific way of building your application.

It is the right choice when your data model is genuinely unstructured or semi-structured. Logs, user-generated content with variable fields, IoT sensor data: these use cases benefit from MongoDB's schema flexibility.

Choose MongoDB when ecosystem and community matter. MongoDB has been around since 2009. Every question you might have has been answered on Stack Overflow. Every language has mature drivers. Finding developers who know MongoDB is easy. For a solo developer, this means fewer dead ends when you get stuck.

MongoDB also makes sense when you might need to self-host. The Community Edition is open source and runs on any server. If you want full control over your data and infrastructure, MongoDB gives you that option while Atlas provides the managed alternative.

The Verdict

Convex and MongoDB represent two different philosophies. MongoDB is a database. Convex is a backend platform that includes a database.

For solo developers building React applications that need realtime features, Convex is the faster path. You skip weeks of backend plumbing and focus on your product. The developer experience is polished, the free tier is generous, and the automatic reactivity is genuinely impressive.

For solo developers who want maximum flexibility, proven technology, and a massive ecosystem, MongoDB is the safer long-term bet. You control every layer of your stack. You can swap frameworks, languages, and deployment platforms without changing your database.

If your application is primarily a React web app with realtime requirements, try Convex first. If you are building something that spans multiple platforms, needs complex aggregations, or might outlive any single framework, go with MongoDB.

Sources

All figures checked on 2026-05-28.

• Convex pricing and included limits: convex.dev/pricing
• Convex self-hosting and FSL Apache 2.0 license: docs.convex.dev/self-hosting
• Convex open-source backend and stars: github.com/get-convex/convex-backend
• Convex npm package and version: registry.npmjs.org/convex/latest and weekly downloads at api.npmjs.org/downloads/point/last-week/convex
• MongoDB Atlas pricing and tiers: mongodb.com/pricing
• MongoDB Atlas M0 free-tier limits: mongodb.com/docs/atlas/reference/free-shared-limitations
• MongoDB server versions and release dates: endoflife.date/mongodb and the MongoDB 8.0 release notes
• MongoDB source and stars: github.com/mongodb/mongo
• MongoDB Node.js driver version and weekly downloads: registry.npmjs.org/mongodb/latest and api.npmjs.org/downloads/point/last-week/mongodb
• Mongoose weekly downloads: api.npmjs.org/downloads/point/last-week/mongoose