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Functions Metadata

The tofu metadata functions command is used to print signatures for the functions available in the current OpenTofu version.


Usage: tofu metadata functions [options]

The following flags are available:

  • -json - Displays the function signatures in a machine-readable, JSON format.

Please note that, at this time, the -json flag is a required option. In future releases, this command will be extended to allow for additional options.

The output includes a format_version key, which has value "1.0". The semantics of this version are:

  • We will increment the minor version, e.g. "1.1", for backward-compatible changes or additions. Ignore any object properties with unrecognized names to remain forward-compatible with future minor versions.
  • We will increment the major version, e.g. "2.0", for changes that are not backward-compatible. Reject any input which reports an unsupported major version.

We will introduce new major versions only within the bounds of the OpenTofu 1.0 Compatibility Promises.

Format Summary

The following sections describe the JSON output format by example, using a pseudo-JSON notation. Important elements are described with comments, which are prefixed with //. To avoid excessive repetition, we've split the complete format into several discrete sub-objects, described under separate headers. References wrapped in angle brackets (like <block-representation>) are placeholders which, in the real output, would be replaced by an instance of the specified sub-object.

The JSON output format consists of the following objects and sub-objects:

Function Signature Representation

Code Block
"format_version": "1.0",

// "function_signatures" describes the signatures for all
// available functions.
"function_signatures": {
// keys in this map are the function names, such as "abs"
"example_function": {
// "description" is an English-language description of
// the purpose and usage of the function in Markdown.
"description": "string",

// "return_type" is a representation of a type specification
// that the function returns.
"return_type": "string",

// "parameters" is an optional list of the positional parameters
// that the function accepts.
"parameters": [


// "variadic_parameter" is an optional representation of the
// additional arguments that the function accepts after those
// matching with the fixed parameters.
"variadic_parameter": <parameter-representation>
"example_function_two": {}

Parameter Representation

A parameter representation describes a parameter to a function.

Code Block
// "name" is the internal name of the parameter
"name": "string",

// "description" is an optional English-language description of
// the purpose and usage of the parameter in Markdown.
"description": "string",

// "type" is a representation of a type specification
// that the parameter's value must conform to.
"type": "string"