Golem 1.5 features — Part 12: REPL

Introduction

This post is part of a series showcasing new Golem 1.5 features (releasing end of April 2026). It assumes reader familiarity with Golem and references prior posts in the series for background. Check the other Golem-related posts for more information.

Testing agents with a REPL

The Golem REPL serves as an important element of testing agents during development. Previously, it relied on Rib, a custom scripting language. However, since Golem moved to code-first routes, maintaining a separate scripting language became redundant.

TypeScript REPL

Golem removed Rib entirely and made it available as a standalone tool for potential wasmtime integration. The new primary REPL is a real TypeScript REPL with agent client classes from bridge libraries preconfigured globally.

The TypeScript REPL works just like you would expect and supports calling any agent type in a type-safe manner, regardless of the agent’s implementation language.

CLI commands from the REPL:

Users can run all the usual commands such as build, deploy, or inspecting agent logs without leaving the REPL using either . or : prefixes.

Running scripts:

TypeScript scripts can execute non-interactively:

const c2 = await CounterAgent.get("c2");
await c2.increment();
await c2.increment();

$ cat test.ts
const c2 = await CounterAgent.get("c2")
await c2.increment()
await c2.increment()

$ golem repl --script-file test.ts --yes
2

Rust REPL

A Rust REPL exists but is very slow because it has to continuously recompile things. It’s retained primarily for Rust script execution where performance impact is less significant.

let c3 = CounterAgent::get("c3").await.unwrap();
c3.increment().await;
c3.increment().await;

$ cat test.rs
let c3 = CounterAgent::get("c3").await.unwrap();
c3.increment().await;
c3.increment().await;

$ golem repl --script-file test.rs --language rust --yes
2

Scala and MoonBit

Scala and MoonBit don’t have any REPL implementation in Golem 1.5, though the TypeScript and Rust REPLs fully support agents written in those languages.