The programmable open source core ledger for fintech — build money-moving applications with atomic multi-posting transactions, account-based modeling, and Numscript, a built-in DSL for financial logic.
Formance Ledger is a programmable financial core ledger designed to be the accounting backbone of modern fintech applications. Built in Go and backed by PostgreSQL, it provides atomic multi-posting transactions, account-based asset modeling, and a powerful domain-specific language called Numscript that lets developers encode complex financial rules without building fragile imperative logic.
Unlike generic databases or simple accounting libraries, Formance Ledger treats money movement as a first-class concern. Every transaction is recorded as a series of postings that move assets between named accounts, with full idempotency guarantees and immutable audit logs. The ledger enforces double-entry bookkeeping at the database level, making it impossible to create money or lose track of balances — a critical requirement for regulated fintech applications.
The platform is designed to fit into a microservices architecture. It ships as a standalone binary or Docker image and can be deployed as a dedicated service behind an HTTP/REST API. It also supports a Kubernetes operator deployment mode for production workloads. A built-in replication pipeline allows ledger logs to be shipped to OLAP data stores such as ClickHouse or Elasticsearch for analytics, without compromising the transactional source of truth.
Formance Ledger is the core of the broader Formance Platform, which adds payment orchestration, webhooks, and developer tooling — but the ledger works equally well as a standalone microservice for teams building custom financial infrastructure from scratch.
users:1234, fees:gateway) allow fine-grained ownership tracking of any asset denominationArchitecture: Formance Ledger follows a clean microservices pattern with a server process (API) and a separate worker process for background tasks such as bucket cleanup and replication pipelines. The internal package structure separates concerns clearly: the internal/ directory contains the core domain model (accounts, transactions, postings, logs), the controller layer, storage adapters, the Numscript virtual machine, and the replication subsystem. The server is built on go-chi for HTTP routing with CORS support, and uses Uber’s fx dependency injection framework for modular wiring.
Tech Stack: The project is written in Go and targets PostgreSQL as its primary transactional datastore via the uptrace/bun ORM and jackc/pgx driver. Numscript is compiled using an ANTLR-generated parser (antlr/antlr4) and executed by a custom virtual machine in internal/machine/vm/. Background message publishing uses Watermill for event-driven fan-out. Replication drivers exist for ClickHouse (ClickHouse/clickhouse-go), Elasticsearch (olivere/elastic), HTTP, Kafka via NATS (nats-io/nats.go), and stdout. OpenTelemetry (go.opentelemetry.io/otel) is wired for both metrics and tracing.
Code Quality: The codebase has strong test coverage using Ginkgo/Gomega BDD-style tests and includes generated test scaffolding via go:generate directives. Integration tests use ory/dockertest to spin up real PostgreSQL containers. The project maintains separate test files per major component (accounts, transactions, balances, moves, volumes), uses go.uber.org/mock for interface mocking, and includes a dedicated test/ directory with test server utilities. Code generation is used for storage layer mocks and driver factory boilerplate, reducing human error in repetitive patterns.
What Makes It Unique: The Numscript DSL is the standout differentiator — it allows engineers to encode financial rules (allocations, overdraft controls, asset routing) as scripts that the ledger evaluates atomically against live balances at transaction time, catching constraint violations before they reach the database. Combined with the multi-ledger namespacing, OLAP replication pipeline, and schema-level Chart of Accounts enforcement, Formance Ledger provides a level of financial modeling sophistication that generic databases or simple accounting libraries cannot match. The project maintains parallel stable release lines (v2.2, v2.3, v2.4) with frequent patch releases, indicating mature operational discipline.
Formance offers enterprise support through the Formance Platform, which wraps the open source ledger with payment orchestration, a management console, hosted cloud options, and commercial SLAs. The Kubernetes operator deployment mode — required for production use per the official documentation — is open source and available at github.com/formancehq/operator. Enterprise users get access to the Formance Cloud (managed), priority support, and integration assistance. Community support is provided through GitHub Discussions.
No Code Platforms · AI Development · Developer Tools
Visual LLM workflow platform with RAG pipelines, agent capabilities, and model management for building production AI applications.
Developer Tools · Game Development · Design Tools
Free, MIT-licensed 2D and 3D game engine with one-click multi-platform export and no royalties.
Developer Tools · Databases · Search
The open-source Postgres development platform that replaces Firebase with authentication, real-time APIs, edge functions, storage, and vector embeddings — all built on PostgreSQL.