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Databases · head to head

FaunaDB vs MongoDB

FaunaDB logo

FaunaDB

Databases

Document-relational database whose hosted service closed in 2025 and whose core is now unmaintained Apache 2.0 code.

From
Free
Rated
-
Full reviewWebsite
MongoDB logo

MongoDB

Technology

The developer data platform

From
Free
Rated
-
Full reviewWebsite

The short version

  • Each has a real cost: FaunaDB the hosted service was wound down in 2025, so there is no managed Fauna to buy; every remaining user either operates a JVM cluster themselves or migrates, and both are projects rather than tasks.; MongoDB 16 MB maximum document size limits large single objects
  • They diverge on capability: FaunaDB covers Document-relational model, MongoDB covers Document model.
  • Prices and features above were last checked on 30 August 2026.

Where they differ

Only the attributes on which FaunaDB and MongoDB actually diverge.

Attributes where FaunaDB and MongoDB differ
AttributeFaunaDBMongoDB
Pricing modelfreemiumUnknown
PlatformsWebCloud (Atlas), Self-hosted, Multi-cloud (AWS, Google Cloud, Azure)
CategoryDatabasesTechnology
Founded20122007

Identical on both: starting price (Free), free tier (Yes), user rating (Not yet rated).

What each one covers

Drawn from each product's published feature list. An absence here means we hold no record of it - not that the product lacks it.

Only in FaunaDB

  • Document-relational model
  • FQL v10
  • Distributed ACID transactions
  • HTTPS access
  • User-defined functions
  • Attribute-based access control
  • Document history
  • Event streaming

Only in MongoDB

  • Document model
  • Distributed architecture
  • ACID transactions
  • Real-time analytics
  • Full-text search
  • Time series data
  • Geospatial queries
  • Aggregation framework

What people use each for

The jobs each tool is most often brought in to do.

FaunaDB

  • Keeping an existing Fauna-backed application alive on self-hosted infrastructure while a migration is planned and fundednot MongoDB
  • Extracting historical data from a Fauna dataset that can no longer be reached through the hosted APInot MongoDB
  • Studying a production implementation of deterministic distributed transactions, since the full server source is now readable under Apache 2.0not MongoDB
  • Forking the engine deliberately, where an organisation has JVM and distributed-systems staff and wants a document-relational store it fully controlsnot MongoDB

MongoDB

  • Mobile applicationsnot FaunaDB
  • Content managementnot FaunaDB
  • Real-time analyticsnot FaunaDB
  • IoT applicationsnot FaunaDB
  • Gaming backendsnot FaunaDB

Where each one falls short

Documented limitations, not opinions. Every one is a constraint you would hit in normal use.

FaunaDB

  • The hosted service was wound down in 2025, so there is no managed Fauna to buy; every remaining user either operates a JVM cluster themselves or migrates, and both are projects rather than tasks.
  • The open-sourced repository has had no substantive activity since May 2025 and the drivers were frozen alongside it, so you inherit responsibility for security patches in a Scala distributed database that almost nobody else is running.
  • FQL has no wire or dialect compatibility with anything else, so migrating off is a rewrite of every query, index and access rule in the application rather than a data export.
  • No BI tool, ORM or CDC connector speaks FQL, so reporting and analytics always required exporting the data first, and that export tooling is now also unmaintained.
  • The community was small before the shutdown and has dispersed since, so operational answers, tuning advice and people who have run a Fauna cluster in anger are all scarce when something breaks.

MongoDB

  • 16 MB maximum document size limits large single objects
  • No native JOIN support for relational data operations
  • Higher memory usage due to storing field names with each document
  • Eventual consistency in distributed deployments can cause data stale reads

Pricing, plan by plan

FaunaDB

Free
  • FreeFree
    • 100K read ops
    • 50K write ops
    • 1GB storage
  • Pro$25/month
    • Pay per use
    • Priority support
    • Advanced features

MongoDB

Free
  • M0Free
    • 512 MB storage
    • Learning and exploration
  • M2$9/month
    • 2 GB storage
    • Development and testing
  • M5$25/month
    • 5 GB storage
  • M10+$56.94/month
    • Dedicated clusters for production

Which should you pick?

Choose FaunaDB if

  • You need document-relational model.
  • You want to start without paying.
  • You also want fql v10.
FaunaDB review

Choose MongoDB if

  • You need document model.
  • You want to start without paying.
  • You work on Cloud (Atlas), Self-hosted, Multi-cloud (AWS, Google Cloud, Azure).
  • You also want distributed architecture.
MongoDB review

Questions people ask

Is FaunaDB or MongoDB better?
Neither clearly leads. FaunaDB starts at Free and MongoDB at Free, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
Which is cheaper, FaunaDB or MongoDB?
FaunaDB starts at Free and MongoDB at Free.
Does FaunaDB or MongoDB run on more platforms?
FaunaDB runs on Web. MongoDB runs on Cloud (Atlas), Self-hosted, Multi-cloud (AWS, Google Cloud, Azure).
Can I use FaunaDB for free?
Both have a free tier, so you can try either at no cost before committing.
What is FaunaDB best used for?
FaunaDB is most often used for keeping an existing fauna-backed application alive on self-hosted infrastructure while a migration is planned and funded, extracting historical data from a fauna dataset that can no longer be reached through the hosted api, studying a production implementation of deterministic distributed transactions, since the full server source is now readable under apache 2.0, forking the engine deliberately, where an organisation has jvm and distributed-systems staff and wants a document-relational store it fully controls. Of those, keeping an existing fauna-backed application alive on self-hosted infrastructure while a migration is planned and funded and extracting historical data from a fauna dataset that can no longer be reached through the hosted api are not what MongoDB is typically brought in for.
What can FaunaDB do that MongoDB cannot?
FaunaDB covers Document-relational model, FQL v10, Distributed ACID transactions, HTTPS access. MongoDB covers Document model, Distributed architecture, ACID transactions, Real-time analytics.

Answered from the vendors’ own pages

FaunaDB: Can I still sign up for Fauna as a service?

No. Fauna Inc. wound down the hosted service in 2025 and the company website is no longer serving. The only way to run Fauna now is to build and operate the open-sourced server yourself.

MongoDB: Does MongoDB offer a free tier?

Yes. MongoDB Atlas offers an M0 free tier with 512 MB storage for learning and exploration, plus paid options starting at $9/month for M2 with 2 GB storage.

Source
FaunaDB: What licence is the open-sourced code under?

Apache 2.0, with the copyright held by a FaunaDB Foundation. That is a permissive OSI licence with no competing-use clause, so you may run it, modify it and even offer it as a service.

MongoDB: Can I self-host MongoDB?

Yes. You can run MongoDB Community Edition on your own servers, or use MongoDB Enterprise Advanced for self-managed production deployments with enterprise features.

Source
FaunaDB: Is the open source version the same software that ran the cloud?

It is the core database engine. The control plane, billing, dashboard and multi-tenant operational tooling that made it a service are not part of the release, so you are running the engine, not the product.

MongoDB: What is the maximum document size in MongoDB?

Documents are limited to 16 MB. For documents exceeding this limit, you can use MongoDB's GridFS API to store files larger than the maximum size.

Source
FaunaDB: What should I migrate to?

There is no drop-in target. Teams that valued the document model with relationships usually land on Postgres with JSONB, and teams that valued the serverless HTTP access pattern usually land on DynamoDB or a managed Postgres with an HTTP driver. Either way the query layer is rewritten.

MongoDB: Does MongoDB support ACID transactions?

Yes. MongoDB supports ACID transactions within a single document by default, and multi-document ACID transactions are available for replica sets and sharded clusters in MongoDB 4.0+.

Source
FaunaDB: How hard is it to self-host?

It builds as a fat JAR and runs as a multi-node JVM cluster. There is an OPERATING.md, but no supported packaging, no operator, no upstream releases and no support contract, so budget for a distributed-systems engineer, not a container.

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