A new WebAssembly runtime written in pure Go launched today, adding another contender to a field already dominated by Rust and C++ implementations. Epsilon positions itself as a zero-dependency alternative for Go developers who want WASM integration without CGo complexity. But here’s the uncomfortable question: Do we really need another Go WASM runtime when Wazero already exists?
What Epsilon Brings to the Table
Epsilon is an open-source WebAssembly 2.0 runtime written entirely in Go with zero external dependencies. Created by developer ziggy42 and released under Apache 2.0, it implements the full WASM 2.0 specification without requiring CGo bindings or C compilers.
The technical appeal is clear: pure Go means effortless cross-compilation, simplified CI/CD pipelines, and a smaller security attack surface. The project includes an interactive REPL for debugging WASM modules, comprehensive spec compliance tests, and a straightforward API for embedding WASM execution into Go applications.
For Go developers frustrated by the complexity of bridging into Rust or C++ ecosystems, Epsilon offers an attractive alternative. No Rust toolchain. No C compiler dependencies. Just Go.
The Wazero Reality Check
Here’s where we need honesty: Epsilon isn’t the first pure-Go WASM runtime. Wazero, backed by Tetrate Labs, already occupies this space—and it’s production-ready.
Wazero released version 1.0 in March 2023 and is used by over 4,600 projects. It offers the same zero-dependency, pure-Go approach as Epsilon but adds dual runtime modes: a universal interpreter and a compiler mode that delivers 10x performance improvements on amd64 and arm64 architectures. It’s mature, battle-tested, and API-stable.
For production use, the choice is clear: use Wazero. It has the adoption numbers, the performance benchmarks, and the organizational backing that production teams require.
So why does Epsilon exist? Runtime proliferation isn’t automatically beneficial—fragmentation dilutes ecosystem attention and splits maintenance efforts. The Go community would be better served by consolidating around one excellent WASM runtime rather than maintaining multiple immature alternatives.
When Epsilon Makes Sense Anyway
Despite Wazero’s dominance, Epsilon has legitimate use cases that justify its existence.
For educational purposes, Epsilon’s codebase may be simpler and more accessible than Wazero’s. Students learning WebAssembly internals benefit from having multiple implementations to study, each with different architectural approaches.
For experimentation, Epsilon offers a fresh foundation without the constraints of Wazero’s established architecture. Researchers testing new ideas can fork and modify Epsilon without navigating years of legacy decisions.
For prototyping, quick integration matters more than production-grade performance. Epsilon’s straightforward API and built-in REPL make it attractive for proof-of-concept work where developer velocity trumps runtime speed.
The REPL deserves specific mention—Wazero doesn’t include one. For developers iterating on WASM modules during development, Epsilon’s interactive environment provides immediate feedback that Wazero users must build themselves.
Performance vs Simplicity
The fundamental trade-off hasn’t changed: pure Go implementations face inherent performance limitations compared to Rust or C++ runtimes with optimizing compilers.
Wasmtime, the industry-standard Rust implementation maintained by the Bytecode Alliance, uses the Cranelift compiler to generate highly optimized machine code. For workloads where performance matters—edge computing, serverless cold starts, high-throughput APIs—Wasmtime’s speed advantage is measurable and significant.
Wazero’s compiler mode closes much of this gap, delivering 10x improvements over its interpreter on supported architectures. Epsilon hasn’t published performance benchmarks, but as a pure interpreter, it will likely trail both.
The counter-argument is that not every project needs maximum performance. Simplicity, debuggability, and ease of integration have value. For internal tools, development workflows, and moderate-scale deployments, Go’s runtime overhead may be acceptable in exchange for implementation clarity.
Choose based on your priorities: need speed? Use Wasmtime or Wazero’s compiler mode. Need simplicity? Epsilon or Wazero’s interpreter will serve you well. Need multi-language embeddings? Wasmtime supports Rust, C, C++, Python, .NET, Go, and Ruby.
The Ecosystem Question
WebAssembly adoption is accelerating across edge computing, serverless platforms, plugin architectures, and blockchain applications. As use cases multiply, the runtime landscape is consolidating around a few strong options while simultaneously sprouting new experimental projects.
This tension—consolidation versus proliferation—defines the current moment. The Bytecode Alliance pushes standardization through Wasmtime. Cloud providers build on established runtimes. But new implementations like Epsilon keep appearing, each promising a slightly different approach.
Is this healthy competition or wasteful fragmentation? The answer depends on what you value. Multiple implementations strengthen specifications by exposing edge cases and ambiguities. But they also divide developer attention, complicate ecosystem tooling, and create maintenance burden.
For production use, betting on established runtimes remains the prudent choice. Wasmtime for maximum performance and multi-language support. Wazero for Go-native deployments. Epsilon for education and experimentation.
What This Means for Your Project
If you’re integrating WebAssembly into a Go application today, default to Wazero unless you have specific reasons to do otherwise. Its maturity, performance, and adoption numbers make it the obvious choice for serious work.
Consider Epsilon if you’re learning WASM internals, need an interactive REPL for development, or want to experiment with runtime implementation ideas. But understand that you’re choosing an early-stage project over a production-proven alternative.
The broader lesson is that runtime proliferation isn’t solving the real challenges facing WebAssembly adoption—specification complexity, tooling maturity, and ecosystem fragmentation are bigger problems than lack of implementation choices.
The Go WASM ecosystem doesn’t need three runtimes. It needs one excellent one—and Wazero is already there.
