OpenSpec Examples — AWS RDS PostgreSQL Terraform Module

Reference material for the blog post at https://notes.keiran.io/posts/OpenSpec/

This repository contains three independently generated Terraform modules for AWS RDS PostgreSQL, each produced by a different AI coding assistant using the same prompt and the same OpenSpec workflow. The outputs are preserved as-is so readers can compare how each assistant interpreted the requirements, structured the code, and approached testing and documentation.

The Prompt

Every assistant received identical instructions:

"I want to create terraform code for AWS PostgreSQL suitable for running Non-Production and Production workloads. I want to ensure it is unit tested using the Terraform unit testing framework and documented with examples for a variety of use cases."

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Directories

Directory	Assistant
claude-billing-postgresql/	Claude Code (Anthropic Sonet)
gemini-billing-postgresql/	Gemini CLI (Google) Gemini 3 Auto
opencode-billing-postgresql/	OpenCode (with Pickle)

OpenSpec Artifacts

Each directory contains the full OpenSpec change artifacts that drove the implementation. These live under openspec/changes/archive/ and include:

• proposal.md — the "why and what" written by the assistant before writing any code
• design.md — the technical design document
• specs/ — per-capability specifications the assistant used as a contract during implementation
• tasks.md — the task list the assistant worked through

These artifacts are what distinguish the OpenSpec workflow from a plain prompt-to-code approach: the assistant reasons about and documents the design before touching any files.