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Files and Directories

File Extension

Code in the OpenTofu language is stored in plain text files with the .tf file extension. There is also a JSON-based variant of the language that is named with the .tf.json file extension.

Files containing OpenTofu code are often called configuration files.

Text Encoding

Configuration files must always use UTF-8 encoding, and by convention usually use Unix-style line endings (LF) rather than Windows-style line endings (CRLF), though both are accepted.

Directories and Modules

A module is a collection of .tf and/or .tf.json files kept together in a directory.

An OpenTofu module only consists of the top-level configuration files in a directory; nested directories are treated as completely separate modules, and are not automatically included in the configuration.

OpenTofu evaluates all of the configuration files in a module, effectively treating the entire module as a single document. Separating various blocks into different files is purely for the convenience of readers and maintainers, and has no effect on the module's behavior.

An OpenTofu module can use module calls to explicitly include other modules into the configuration. These child modules can come from local directories (nested in the parent module's directory, or anywhere else on disk), or from external sources like the Public OpenTofu Registry.

The Root Module

OpenTofu always runs in the context of a single root module. A complete OpenTofu configuration consists of a root module and the tree of child modules (which includes the modules called by the root module, any modules called by those modules, etc.).

  • In OpenTofu CLI, the root module is the working directory where OpenTofu is invoked. (You can use command line options to specify a root module outside the working directory, but in practice this is rare.)
  • In TACOS (TF Automation and Collaboration Software), the root module for a workspace defaults to the top level of the configuration directory (supplied via version control repository or direct upload), but the workspace settings can specify a subdirectory to use instead.