---
title: "Evolution of the Heroku CLI: 2008-2017"
description: "Between 2008 and 2017, Heroku's CLI evolved from Ruby (v1–v3) through Go/Node versions v4 and v5 to a pure Node v6 implementation. The rewrite addressed slower Windows performance, separation of the CLI's runtime from users' Ruby environments, migration to API v3, and limitations in Ruby-based plugin dependencies. V4 kept existing command syntax and output while adding features such as non-TTY color suppression and --json output; its Go core used Node for plugins, and the CLI became a collection of core plugins that could also be developed and installed independently. The team migrated commands incrementally, then added Flow, Babel, and improved tests, including Jest tests that run the flag parser. The resulting foundation supports modular, tested feature development, with cli-engine and more interactive interfaces planned."
---

# Evolution of the Heroku CLI: 2008-2017

[Heroku](https://yomu.fyi/company/heroku) · Jeff Dickey · Aug 15, 2017

**Type:** Explainer

## Summary

Between 2008 and 2017, Heroku's CLI evolved from Ruby (v1–v3) through Go/Node versions v4 and v5 to a pure Node v6 implementation. The rewrite addressed slower Windows performance, separation of the CLI's runtime from users' Ruby environments, migration to API v3, and limitations in Ruby-based plugin dependencies. V4 kept existing command syntax and output while adding features such as non-TTY color suppression and --json output; its Go core used Node for plugins, and the CLI became a collection of core plugins that could also be developed and installed independently. The team migrated commands incrementally, then added Flow, Babel, and improved tests, including Jest tests that run the flag parser. The resulting foundation supports modular, tested feature development, with cli-engine and more interactive interfaces planned.

## Context

The Ruby CLI created performance differences across platforms, made it difficult to isolate the CLI's Ruby and gem environment from a user's application, complicated plugin dependency management, and needed to move to API v3. A full replacement would also have required a lengthy migration and painful QA process.

## Approach / What changed

Heroku preserved familiar command syntax and output while migrating commands incrementally. The new design used a Go core with a separate Node runtime for plugins, treated the CLI itself as a collection of core plugins, and added Flow, Babel, Jest, improved test coverage, and parser-aware tests.

## Takeaways

- The v4 CLI retained existing command syntax and output to reduce disruption, while adding non-TTY color suppression and --json output for scripting.
- The plugin architecture made the CLI a modular collection of core plugins; user plugins could become preinstalled core plugins without modifying the plugin itself.
- CLI v6 tests use Jest and execute the flag parser, helping catch commands whose tests pass despite missing or incorrect flag definitions.

**Tags:** [Architecture](https://yomu.fyi/topic/architecture), [Go](https://yomu.fyi/topic/go), [Node.js](https://yomu.fyi/topic/node-js), [Ruby](https://yomu.fyi/topic/ruby), [Testing](https://yomu.fyi/topic/testing)

- Source: [Heroku](https://www.heroku.com/blog/evolution-of-heroku-cli-2008-2017)
- Source URL: https://www.heroku.com/blog/evolution-of-heroku-cli-2008-2017
- Ingested by Yomu: 2026-09-09T14:25:35.565Z

[Read original post](https://www.heroku.com/blog/evolution-of-heroku-cli-2008-2017)