phase4

Overview

phase4 is an open-source Java library for embedding AS4 message sending and receiving in an existing system. It is a practical fit for development teams building their own e-delivery integrations, but its value depends on having the Java expertise and integration capacity to put it to work.

Its broad profile support and Apache 2.0 license are compelling for custom implementations. It is not a standalone project, and missing multi-hop, split, and join capabilities rule it out for systems that depend on those AS4 functions.

Key features

Built-in Peppol and CEF eDelivery support gives implementers a starting point for two established profiles. Documentation also covers BDEW, DBNAlliance, eDelivery2, EESPA, ENTSOG, EUCTP, and HR eDelivery, making the library relevant to teams whose integrations need to accommodate several profile requirements. That breadth does not remove the work of embedding it in an application.

The preferred configuration file is application.properties, with system properties and environment variables as alternatives. Keystores and truststores support JKS and PKCS12 formats, giving teams familiar options for managing certificates. Java 17 is the minimum; Java 21 or later is recommended for performance, so deployments on older Java versions are not a fit.

Automated unit and integration tests cover many configurations, but end-to-end checks against a real remote system are a separate matter. The testing guide says an official Peppol AP certificate is required to test sending to or receiving from an existing Peppol service provider. Teams should arrange that access as part of validating a Peppol deployment, rather than treating automated tests as a substitute.

AS4 multi-hop and split and join are not implemented. This is a material limitation for architectures that require those capabilities, even if the library otherwise matches their Java and profile needs.

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. There is no paid tier in the stated plan; the trade-off is that the library must be manually integrated into an existing system, so the zero software price does not eliminate implementation work.

Platforms

phase4 is intended to run on Windows, Linux, Mac, and AWS, and supports self-hosted deployment. Its Java 17 minimum and Java 21-or-later performance recommendation shape the practical platform choice more than the operating system does. The maintainer identifies Vienna, Austria as their location; users seeking commercial support can contact the maintainer by email.

Who it's for

Choose phase4 if you are building or extending a Java system and want an open-source foundation for AS4 messaging across Peppol, CEF eDelivery, or one of its other documented profiles. It is especially suited to teams that can handle integration, certificate configuration, and remote-system validation themselves.

It is a poor choice for buyers looking for a ready-to-run e-invoicing service, teams constrained to Java versions below 17, or projects that require AS4 multi-hop, split, or join. The Apache 2.0 license permits a free starting point, but the need to integrate and validate the library makes it a developer-facing option rather than a turnkey product.

Pros and cons

• Pro: Apache 2.0 licensing and a free plan remove software fees for teams able to integrate the library.
• Pro: Built-in Peppol and CEF eDelivery support, plus several additional documented profiles, give custom implementations a broad starting point.
• Pro: Configuration through a properties file, system properties, or environment variables, with JKS and PKCS12 support for keystores and truststores, offers familiar deployment controls.
• Con: Manual integration is required, so it does not suit organizations seeking a standalone application.
• Con: AS4 multi-hop, split, and join are not implemented, excluding projects that need those capabilities.
• Con: Real Peppol provider testing requires an official AP certificate, adding a dependency to end-to-end validation.

Alternatives

For a broader Electronic Invoicing Software comparison, start with the category directory.

• Billit is a better direction for readers seeking a freemium Peppol e-invoicing product rather than a Java library; its free plan covers sales invoices only and has limited functionality.
• Holodeck B2B is another free open-source Java option, under GNU GPL 3, and requires Java 11 or later rather than phase4's Java 17 minimum.
• B2Brouter suits readers considering a freemium web or API service; its Basic plan is billed forever at no cost and caps usage at 10 contacts, 24 transactions per year, and one user.
• BillingEngine is a freemium API and web alternative with a free plan capped at three invoices, three quotes, three receipts per month, and one user.
• Domibus is a free alternative for teams looking for an EU Public Licence downloadable sample implementation rather than phase4's Apache-licensed library.
• ONESOURCE Pagero is a freemium API and web alternative from Thomson Reuters.
• PeppolSoft is a freemium API and web alternative whose free Buyer plan includes receiving, a web portal, and an app.
• Tradeshift is a paid API and web alternative with a free tier covering up to 30 invoices per quarter.

Verdict

phase4 is a strong choice for Java teams that need an open-source AS4 library, value its profile coverage, and can own integration and validation. Its main advantage is a capable, zero-price starting point under Apache 2.0; its main reason to look elsewhere is that it is not standalone and omits multi-hop, split, and join support.