MongoDB, Inc. v. FerretDB Inc. is a pending case in the United States District Court for the District of Delaware between MongoDB, which develops a document database that it describes as “free and source-available”, and FerretDB, which develops an open source database that presents a MongoDB-compatible interface on top of PostgreSQL. MongoDB sued in May 2025 for patent infringement, false advertising and trademark dilution.[1] FerretDB answered and counterclaimed, and on 2026-09-25 the court refused to dismiss FerretDB’s non-patent counterclaims.[2][3] The licences that govern MongoDB’s own software are covered in MongoDB licensing.
Background
MongoDB’s complaint describes a licensing arrangement for its source-available database “designed to promote the benefits of the source-available model by encouraging open collaboration, while prohibiting freeriders from selfishly exploiting MongoDB’s technology for their own commercial gain”. MongoDB licenses its database server under its Server Side Public License (SSPL) v1.0 for versions released after 2018-10-16, with the stated aim of requiring “that enhancements to MongoDB be released to the community”, and its drivers under the Apache License 2.0.[4] FerretDB, founded in 2021 and originally named MangoDB, built a product that the complaint says it markets as a “MongoDB alternative” allowing users to “turn their Postgres services into MongoDB as a service”. In 2025 FerretDB released version 2.0, which it described as the result of a collaboration with Microsoft, and announced a FerretDB Cloud service.[1]
The dispute
MongoDB’s claims are not based on its software licence. It alleges that FerretDB infringes four patents on aggregation framework architecture and the optimisation of database operations, and that FerretDB “is not licensed or otherwise authorized to practice” them. It alleges false advertising because FerretDB’s website said that it “mimics the behavior of MongoDB in every possible way”, while FerretDB’s own compatibility documentation showed it lacked nearly a third of MongoDB’s commands and tools, including role management commands, and that FerretDB 2.0 did not run on Arm processors. It alleges trademark dilution through FerretDB’s repeated use of the MongoDB marks. MongoDB says it sent letters on 2023-11-03 and 2023-11-29 and a final letter with patent claim charts on 2025-05-16 before suing.[1]
FerretDB answered in September 2025 and, in amended counterclaims filed on 2025-11-05, sought declarations that the patents are invalid and not infringed and alleged that MongoDB had engaged in false advertising, defamation and tortious interference, including by stating on its website that FerretDB infringes its patents. MongoDB moved to dismiss those three counterclaims as preempted by federal patent law, which protects statements about patent infringement unless made in bad faith.[2]
Decision or outcome
On 2026-09-25 the court denied MongoDB’s motion. It found that FerretDB’s counterclaims were “arguably based largely on statements that do not directly concern patent rights”, since “the bulk of the statements in the Press Release and the Letters are not related to patents”, and that it was premature to resolve preemption on a motion to dismiss.[3] No ruling has yet been made on MongoDB’s patent, false advertising or trademark claims.
Significance for software licensing and SAM practice
Source-available licences such as MongoDB’s restrict what others may do with the vendor’s code, but they do not stop a third party from writing its own compatible implementation. This case tests the other rights a vendor may assert against such an implementation, patents and trademarks, and how far compatibility claims can be made in marketing.[1] It sits alongside Elasticsearch v. Amazon, where Elastic relied on its trademark against a third-party service based on its earlier open source code.
Lessons learned
- A compatible alternative to a source-available product avoids the vendor’s copyright licence but can still face patent and trademark claims. MongoDB’s claims rest on its patents and marks, not on its licence.[1]
- Treat claims that an alternative is a “drop-in replacement” as a hypothesis to test against your own workloads, commands and tools. The complaint relies on the alternative’s own compatibility documentation to allege that it lacked many commands and some hardware support.[1]
- Source-available licences and patents are separate: the SSPL governs copying MongoDB’s code, while patent rights reach independent implementations. The SSPL is a copyright licence for MongoDB’s server code, but the asserted patents cover methods that, MongoDB alleges, FerretDB practises without a licence.[1][4]
- Before standardising on an alternative, record which vendor tools, drivers and features it supports and which it does not. Compatibility gaps are at the centre of both sides’ false advertising claims.[1][2]