Freedom251 › Stream Analytics Software
Esper
What Esper is
Esper is a complex event processing and streaming analytics system for Java and .NET applications. It includes a language, compiler and runtime: developers express operations on events and time using Event Processing Language (EPL), which extends SQL, then compile EPL into bytecode that can be packaged in JAR files. Esper and its .NET counterpart, NEsper, are embedded in application processes rather than run as standalone servers. The runtime processes streams in memory; Esper describes it as memory-efficient and low-latency, and says it does not depend on external storage or services.
The listed adapters handle input and output through CSV, JMS, HTTP, Kafka, databases and sockets, while JMX can expose metrics. Queries can combine events with external information, including web services and relational databases, using SQL-query or method-invocation joins. Esper Enterprise Edition adds a scale-out architecture built on Apache Kafka and Apache Zookeeper, with elastic scaling, load balancing, fault tolerance and multi-datacenter support. EsperTech lists business process monitoring, financial applications such as fraud detection, network and application monitoring, and sensor networks among its use cases. Esper 9.0.0 is listed under GNU GPL (GPL v2), with commercial redistribution licenses also offered by EsperTech.
Who it suits
Esper suits Java and .NET developers building applications that analyze event streams, including monitoring, financial and sensor network use cases. It is also relevant to companies that need to redistribute Esper or NEsper commercially, or want production support from EsperTech.
What it does well
- EPL extends SQL for expressions over events and time.
- Compiles EPL into bytecode distributable in JAR files.
- Adapters cover CSV, JMS, HTTP, Kafka, databases and sockets.
- Can join events with web services and relational databases.
- Free Esper 9.0.0 release is listed under GNU GPL (GPL v2).
What to know first
- Esper and NEsper are embedded components, not standalone servers.
- Scale-out capabilities are described for Enterprise Edition.
- EsperTech offers commercial redistribution licenses.
- Developer Seat support excludes bug fixes and training.
Plans
| Plan | Billed and limits | Price |
|---|---|---|
| Esper 9.0.0 | GNU GPL (GPL v2) | Free |
| Esper Open Source | GPLv2 license · Java/JVM and .NET/NEsper · software supplied as-is | Free |
| Esper support | per year and per instance or per seat · Production support: Bronze, Silver, Gold · Development support: Developer Seat | On request |
| Esper Enterprise Edition | closed-source commercial product · horizontal scaling · REST services · GUI · JDBC/JMX · commercial support | On request |
| EsperHA | high-availability add-on · state resilience · fast recovery · enterprise support | On request |
As espertech.com lists them, read 3 Oct 2026. The maker's own page has the final word.
Getting started
- Visit the Esper website.
- Choose the Esper 9.0.0 GNU GPL release or contact EsperTech about commercial redistribution licensing.
- Use the Java or .NET component in the corresponding application process.
- Write event operations in EPL and compile them into bytecode for JAR packaging.
Verdict
Choose Esper if you are building Java or .NET software that needs complex event processing with SQL-derived event queries and an embeddable runtime. Look elsewhere if you need a standalone server, or evaluate Esper Enterprise Edition for the listed scale-out architecture and commercial licensing for redistribution.
Questions
Is Esper free?
Esper 9.0.0 is listed as free under GNU GPL (GPL v2). EsperTech also offers commercial redistribution licenses.
Which languages does Esper support?
Esper is available for Java, and NEsper is its .NET counterpart. The listed supported languages are Java and C#.
Does Esper run as a standalone server?
No. Esper and NEsper are described as components embedded in Java and .NET processes.
What integrations does Esper list?
Its adapters include CSV, JMS, HTTP, Kafka, database and socket input/output. It also lists JMX metrics exposure and joins with web services and relational databases.
What support plans are available?
EsperTech lists Bronze, Silver and Gold production support, plus a Developer Seat for development questions. Developer Seat covers how-to questions, not software bug fixes or training.
What does Esper Enterprise Edition add?
Its scale-out architecture, built on Apache Kafka and Apache Zookeeper, lists elastic scaling, load balancing, fault tolerance and multi-datacenter support. EsperHQ and EsperJMX can access CEP engines remotely over secured connections with user credentials.
Facts from Esper's own pages
- API documentation
- Official documentation provides separate JavaDoc for the API, compiler, runtime, common modules, Avro and EsperIO. · espertech.com, 15 Oct 2026
- Commercial licensing
- EsperTech offers EULA and OEM licenses that remove GPL copyleft obligations, with redistribution rights for OEMs. · static.espertech.com, 15 Oct 2026
- Company legal name
- The maker identifies itself as EsperTech Inc. · espertech.com, 15 Oct 2026
- Compilation
- The Esper compiler compiles EPL into bytecode that can be packaged in JAR files for distribution and execution. · espertech.com, 3 Oct 2026
- Continuous processing
- The engine stores queries and evaluates incoming events continuously instead of polling stored records. · esper.espertech.com, 15 Oct 2026
- Current release
- The documentation page identifies Esper and EsperIO 9.0.0 as the current release. · espertech.com, 3 Oct 2026
- Deployment model
- Esper and NEsper are embeddable components for Java and .NET processes rather than standalone servers. · espertech.com, 3 Oct 2026
- Developer tooling
- EsperTech provides a free Visual Studio Code extension and EPL language server. · espertech.com, 15 Oct 2026
- Documentation depth
- EsperTech publishes reference manuals, API JavaDocs, examples, training material and a knowledge base across many releases. · espertech.com, 15 Oct 2026
- Downloads
- Core downloads are public, while Enterprise Edition and EsperHA downloads require registration or login. · espertech.com, 15 Oct 2026
- Embedding
- Esper is designed to run inside Java or .NET processes and does not require external services or storage. · espertech.com, 15 Oct 2026
- Enterprise security
- Esper Enterprise Edition says EsperHQ and EsperJMX can access CEP engines remotely over secured connections with user credentials. · espertech.com, 3 Oct 2026
- Event formats
- Supported event representations include Java objects, maps, JSON, XML, object arrays and Avro. · espertech.com, 15 Oct 2026
- Event language
- Its Event Processing Language (EPL) implements and extends SQL for expressions over events and time. · espertech.com, 3 Oct 2026
- Event Processing Language
- Its EPL language extends SQL-style querying with event-time and stream-processing operations. · espertech.com, 15 Oct 2026
- Extension APIs
- Extension points include plug-in loaders, data-flow operators, virtual data windows, method invocation and external service calls. · esper.espertech.com, 15 Oct 2026
- External data
- Esper supports joining external data, including web services, relational databases through SQL-query joins and method invocation joins. · espertech.com, 3 Oct 2026
- Founded
- Esper is documented as created in 2006, with its first public release in early 2006. · en.wikipedia.org, 15 Oct 2026
- Headquarters
- EsperTech lists a mailing address in Wayne, New Jersey, USA. · espertech.com, 15 Oct 2026
- Independent assessment
- Bloor Research describes Esper as an early open-source CEP engine and says commercial licenses are needed for OEM use. · bloorresearch.com, 15 Oct 2026
- Independent deployment finding
- Bloor reports that Esper can run as an embedded component, self-contained stack or Docker container across edge, on-premises and cloud environments. · bloorresearch.com, 15 Oct 2026
- Independent Kafka finding
- Bloor reports that Enterprise Edition can add instances dynamically and use Kafka-based failover when an instance goes down. · bloorresearch.com, 15 Oct 2026
- Independent technical evidence
- A peer-reviewed study selected Esper for reported performance, operator versatility and technological maturity when integrating CEP with message brokers. · pmc.ncbi.nlm.nih.gov, 15 Oct 2026
- Integrations
- The feature list names CSV, JMS, HTTP, Kafka, database and socket input/output adapters, and JMX metrics exposure. · espertech.com, 3 Oct 2026
Where Esper stands on Freedom251
- Stream Analytics Software#2 of 26
- Stream Processing Software#4 of 26