phase4

phase4 is an embeddable Java library for sending and receiving AS4 messages, aimed at teams building messaging into an existing system. Its broad profile support and Apache 2.0 license make it a strong foundation for custom integrations, but it is not a ready-to-run service.

Overview

phase4 focuses on AS4 messaging rather than providing a complete invoicing application. Teams can use it as an on-premise component with Peppol access and UBL support, but must integrate it into their own software. That trade-off suits developers who need control over implementation; organizations seeking a turnkey workflow should look at a managed service instead.

Key features

The library supports Peppol and CEF eDelivery, with additional documented profiles including BDEW, DBNAlliance, eDelivery2, EESPA, ENTSOG, EUCTP, and HR eDelivery. This makes phase4 relevant when an integration must address more than one profile. Profile breadth does not replace the engineering needed to embed the library in an application.

Configuration can be supplied through the preferred application.properties file, system properties, or environment variables. Keystores and truststores support JKS and PKCS12 formats, giving implementers options for certificate configuration. Java 17 is the minimum; Java 21 or later is recommended for performance.

Automated unit and integration tests cover many configurations, but they are distinct from testing against a real remote system. The project’s Peppol testing guide requires an official AP certificate to test sending to or receiving from an existing service provider. Teams should plan for that dependency in their end-to-end validation.

AS4 multi-hop and AS4 split and join are not implemented. Those omissions matter for systems that depend on either capability; phase4 is a weaker fit for those requirements until they are addressed elsewhere.

Pricing

The Open-source library plan costs nothing and is licensed under Apache 2.0. It includes API access, Peppol access, UBL structured formats, and on-premise deployment; tax validation is not included. There is no separate paid tier or free trial. The absence of a software fee is useful for teams able to supply their own integration work, but the plan does not turn the library into a hosted service or remove the need to manage deployment and certificates.

Platforms

phase4 works on Windows, Linux, Mac, and AWS. It is a self-hosted Java library rather than a standalone application, and requires Java 17 or later. Java 21 or later is the recommended choice when performance is a priority.

Who it's for

phase4 is best for development teams embedding AS4 messaging in an existing system, particularly where Peppol, CEF eDelivery, or one of its other documented profiles is required. It is less suitable for buyers who need a complete invoicing product, built-in tax validation, or an integration that avoids Java development. Teams should also confirm that multi-hop and split-and-join support are not requirements.

Pros and cons

Pros: Apache 2.0 licensing and a free plan avoid software fees.

Pros: Support for Peppol, CEF eDelivery, and a range of other profiles gives integrators several protocol options.

Pros: Multiple configuration sources and JKS or PKCS12 certificate stores offer practical setup choices.

Cons: Manual integration into an existing system makes this a developer component, not a ready-to-use service.

Cons: Multi-hop and split-and-join features are not implemented.

Cons: Real Peppol end-to-end testing depends on an official AP certificate.

Cons: Tax validation is not included.

Alternatives

For a broader set of electronic invoicing options, see Electronic Invoicing Software.

Billit is a better fit for buyers who want a freemium invoicing product with Android, iOS, web, and API access; its free license sends Peppol e-invoices but is limited to sales invoices and functionality.

B2Brouter suits teams seeking a web or API service with a permanent free Basic tier, though that tier is capped at 10 contacts, 24 transactions per year, and one user.

Peppox is an option for teams preferring a paid service with Android, iOS, web, and API access; its Company plan includes 1,000 invoices per month before a per-invoice charge applies.

Tungsten Power PDF is the alternative for readers seeking a desktop PDF editor rather than AS4 messaging software.

Arratech Peppol-as-a-Service is another service-oriented Peppol option, with custom pricing.

BillingEngine offers web and API access with a free tier capped at three invoices, three quotes, and three receipts per month for one user.

Holodeck B2B is another free open-source Java option for B2B messaging, with Java 11 or later required.

PeppolSoft offers a free Buyer plan for receiving through its web portal and app, making it a different option for buyers who do not need to embed an AS4 library.

Verdict

Choose phase4 if your team can integrate a Java library and wants a free, Apache-licensed route to AS4 messaging across Peppol and other profiles. Its main advantage is that breadth without a software fee; its main reasons to look elsewhere are the integration burden, missing multi-hop and split-and-join support, and the certificate requirement for real Peppol testing.