OpenTofu Core Codebase Documentation

This directory contains some documentation about the OpenTofu Core codebase, aimed at readers who are interested in making code contributions.

If you're looking for information on using OpenTofu, please instead refer to the main OpenTofu CLI documentation.

OpenTofu Core Architecture Documents

OpenTofu Core Architecture Summary: an overview of the main components of OpenTofu Core and how they interact. This is the best starting point if you are diving in to this codebase for the first time.
Resource Instance Change Lifecycle: a description of the steps in validating, planning, and applying a change to a resource instance, from the perspective of the provider plugin RPC operations. This may be useful for understanding the various expectations OpenTofu enforces about provider behavior, either if you intend to make changes to those behaviors or if you are implementing a new OpenTofu plugin SDK and so wish to conform to them.

(If you are planning to write a new provider using the official SDK then please refer to the Extend documentation instead; it presents similar information from the perspective of the SDK API, rather than the plugin wire protocol.)
Plugin Protocol: gRPC/protobuf definitions for the plugin wire protocol and information about its versioning strategy.

This documentation is for SDK developers, and is not necessary reading for those implementing a provider using the official SDK.
How OpenTofu Uses Unicode: an overview of the various features of OpenTofu that rely on Unicode and how to change those features to adopt new versions of Unicode.

Contributing to OpenTofu: a complete guideline for those who want to contribute to this project.