---
title: "Vibe engineering Effect apps"
description: "Michael Arnaldi shows how source, tests, and diagnostics can guide agents working with Effect."
plain: "Michael Arnaldi says agents should learn Effect from its source and get feedback from diagnostics, tests and lint."
group: source
speaker: "Michael Arnaldi"
date: 2026-05-07
url: https://youtu.be/Wmp2Tku2PrI
sources:
  - url: https://youtu.be/Wmp2Tku2PrI
    title: "Vibe Engineering Effect Apps — Michael Arnaldi, Effectful - YouTube"
    publisher: "Michael Arnaldi"
    note: "Recording; used for source, tests, and diagnostics as agent feedback."
    accessed: "2026-10-01"
---

# Vibe engineering Effect apps

> For agents: start with the [agent guide](https://ratstack.sh/llms.txt). Every page is Markdown by default; add `Accept: text/html` for HTML.

New on /news: [Effect Office Hours 52 with Resonate HQ](/news).

Effect is a TypeScript library for describing work with typed results, failures, and required services.

Michael says an agent should learn a fast-moving library from its source repository. Stale model knowledge and giant prompts are less reliable. [08:51](https://youtu.be/Wmp2Tku2PrI?t=531) [12:59](https://youtu.be/Wmp2Tku2PrI?t=779)

He describes repository feedback from compiler diagnostics, tests, lint checks, saved patterns, and short-lived contexts.

Diagnostics report compiler problems. Lint checks reject code patterns that break project rules. He recommends choosing patterns for the project and model. [30:30](https://youtu.be/Wmp2Tku2PrI?t=1830) [38:15](https://youtu.be/Wmp2Tku2PrI?t=2295) [58:08](https://youtu.be/Wmp2Tku2PrI?t=3488)

## Sources

1. [Vibe Engineering Effect Apps — Michael Arnaldi, Effectful - YouTube](https://youtu.be/Wmp2Tku2PrI)
   Michael Arnaldi. Recording; used for source, tests, and diagnostics as agent feedback. Accessed 2026-10-01.

## Linked from

- Agent guide → An Effect stack so pure (aspirational) Kit Langton will blush. → [Read page](https://ratstack.sh/llms.txt)

- Change log → What changed in the files served here, newest first. → [Read page](https://ratstack.sh/log)

- Full agent guide → An Effect stack so pure (aspirational) Kit Langton will blush. → [Read page](https://ratstack.sh/llms-full.txt)

- Rat Stack lore | rat-stack → Short, source-grounded notes on the ideas and decisions behind rat-stack. → [Read page](https://ratstack.sh/lore)

- Source change history (log.md) → The generated change log as Markdown. → [Read page](https://ratstack.sh/log.md)

- Source-first workflow → Michael Arnaldi says agents should inspect a library's current source instead of trusting stale model knowledge. → [Read page](https://ratstack.sh/lore/agent-source-first-workflow)