Massient

Massient is the company behind MassTransit, the most popular distributed application framework for building message-based applications with .NET.

MassTransit is a modern, lightweight, and feature-rich service bus used by organizations of every size in over 150 countries worldwide. With over 150 million downloads and more than 120,000 deployments around the globe, MassTransit reduces the development time and operational overhead involved in building distributed, event-driven applications.

Features

Business Logic

Saga State Machines

Saga state machines are powerful tools for building sophisticated workflows comprised of states, events, and behaviors. The code-first fluent design language, entirely in C#, provides compile-time confidence that can be unit tested.

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Deployment

Transport Liquidity

Applications using MassTransit can be easily configured to run on different message brokers, including RabbitMQ, Azure Service Bus, and Amazon SQS. An advanced SQL transport is also available, supporting both SQL Server and PostgreSQL.

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Reliability

Exception Handling

Advanced exception handling, including transient retry, broker-based redelivery, and fault message routing ensures your system can adapt to the challenges of distributed systems.

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Business Logic

Routing Slips

Create dynamic and durable distributed transactions with compensation using routing slips, enabling fault-tolerant choreography in your applications.

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Business Logic

Request/Response

Simplify interactions between business components by leveraging fast request and response routing using MassTransit's request client

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Development

In-Memory Test Harness

Create fast in-memory unit tests, as well as end-to-end integration tests, using the test harness to validate your consumers and business logic.

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Operations

Observability

Monitor your consumers, saga state machines, and routing slips using MassTransit's native OpenTelemetry support.

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Deployment

Framework Defined Infrastructure

Using the receive endpoints, consumers, and message types in your code, MassTransit automatically created and/or validates the broker topology, including topics, subscriptions, queues, and exchanges.

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License Pricing

(In US Dollars)

Single Line

Perfect for small organizations with single product line

One product, including all services and deployments
Flat-rate pricing, no per-message or per-endpoint fees
Annual subscription with perpetual downgrade rights
Email support with a standard response time

Multiple Line

Suitable for multiple product lines within an organization

Everything in Single Line
Multiple products, services, and deployments
Guidance for cross-team deployments and scaling

Frequently Asked Questions

Do I need a license for development or test environments?

Your license covers all environments, including environments used for development, testing, staging, and production, within the scope of the license.

Are there limits on developers, services, endpoints, or messages?

Your license includes all developers and services in all environments. You are not charged any additional per-endpoint or per-message fees.

What constitutes a product line in this context?

A product line refers to a single, cohesive software system or family of services that together make up one functional product. For example, an application, platform, or backend supporting a specific business domain is considered a single product line. The license covers all related services, components, APIs, and background processes across all environments (development, testing, staging, and production). Each product line typically has its own release cycle, infrastructure, or codebase. Organizations that operate multiple independent systems or business units can use an organization-wide (multi-line) license, which covers all product lines under one agreement.

What happens if my license expires?

If your license expires, you retain perpetual rights to continue using any MassTransit version released during your active subscription period. A current license is required when upgrading to newer versions. This ensures that an application built and deployed using MassTransit with a valid license will continue to run even after the license has expired.

Will MassTransit v9 be open source?

MassTransit v9 will not be open source under a permissive license like previous versions, but it will remain source-available. The full source code will continue to be hosted on GitHub, accessible to licensed customers and community users with appropriate permissions. This ensures transparency, auditability, and the ability to review or debug the framework while maintaining a commercial licensing model. The codebase, APIs, and development process will remain open for review, but redistribution or modification outside the license terms will require authorization.

What about licensing for agencies or consultancies?

Agencies and consultancies are licensed based on how they engage with their clients. A commercial license is required for any projects that use MassTransit while under the agency’s development or maintenance. If ownership or ongoing maintenance of the application is later transferred to a client, that client must obtain their own MassTransit license to continue updating the software. Agencies can use one multiple line license for all projects they actively maintain, provided those applications remain under their management. This ensures that both development partners and clients are properly licensed for their respective roles.

Is there a free or discounted license available?

Organizations with gross annual revenue under one million (USD) may qualify for a 100% discount on a MassTransit license. This includes full access to all features and functionality of the licensed version, but does not include commercial support (community support remains available through public discussion channels and the official documentation). This program is designed to make it easy for startups, independent developers, and smaller teams to adopt MassTransit early, build confidently, and transition to a commercial support plan as they scale. Once your organization’s annual revenue exceeds one million (USD), you’ll need to pay for a commercial license at your next renewal.

Will there be a free license for non-profits?

Non-profit organizations with annual expenses under one million (USD) may qualify for a 100% discount on a MassTransit license.