A comparison of three document databases—MongoDB, Google Firestore, and Amazon DocumentDB—based on the author's hands-on experience with all three. MongoDB is presented as the most powerful and portable option with rich querying, aggregation pipelines, and vector search, best for complex or vendor-independent projects. Firestore is framed as the easiest entry point for beginners thanks to its serverless model, real-time sync, and generous free tier, though its querying is limited. Amazon DocumentDB offers a MongoDB-compatible API but runs its own storage engine, missing some advanced MongoDB features, and is mainly recommended for teams already committed to AWS. The overall takeaway is that no database is universally best—choose based on team context and project needs.
Questions this post answers
Is Amazon DocumentDB actually running MongoDB under the hood?
No, Amazon DocumentDB is not MongoDB itself but a separate database with its own storage engine built by AWS, wrapped in a MongoDB-compatible API that accepts the same queries and commands. Most basic operations work identically, but advanced features like the full aggregation pipeline and certain query operators may be missing or only partially supported. Teams weighing a move to DocumentDB can track compatibility gaps and migration tips on daily.dev.
What is the Firestore free tier limit for reads and writes?
Google Cloud Firestore's free tier provides 50,000 document reads and 20,000 writes per day at no cost. This is generous enough for learning projects and small side projects to run for a long time without incurring charges, though costs can climb quickly once an app becomes write-heavy in production. Developers comparing free-tier limits across databases can follow Firestore pricing changes on daily.dev.
Should I use Firestore or MongoDB Atlas for my first backend project?
Firestore is better suited for beginners because of its zero-infrastructure serverless setup, generous free tier, and real-time data sync that updates apps instantly without polling. MongoDB Atlas is recommended for more serious or portable projects since it offers a free M0 cluster, powerful querying with the aggregation pipeline, and skills that transfer to most professional backend roles. Developers deciding between Firestore and MongoDB Atlas can compare real-world tradeoffs on daily.dev.