Syntax

The Alloy syntax is easy to read and write. It has two main elements: Attributes and Blocks.

The Alloy configuration syntax is a declarative language for creating programmable pipelines. The order of blocks and attributes in the Alloy configuration file doesn’t matter. The language evaluates all dependencies between elements to determine their relationships.

Comments

Alloy configuration files support single-line // comments and block /* */ comments.

Identifiers

An identifier in Alloy syntax is valid if it contains one or more UTF-8 letters (A through Z, upper- or lowercase), digits, or underscores. It can’t start with a digit.

Attributes and Blocks

Attributes

Use Attributes to configure individual settings. Attributes follow the format ATTRIBUTE_NAME = ATTRIBUTE_VALUE. They can appear as top-level elements or nested within blocks.

The following example sets the log_level attribute to "debug".

alloy
log_level = "debug"

The ATTRIBUTE_NAME must be a valid Alloy identifier.

The ATTRIBUTE_VALUE can be a constant value of a valid Alloy type, such as a string, boolean, or number. It can also be an expression to compute complex values.

Blocks

Use Blocks to configure the behavior of Alloy and its components by grouping attributes or nested blocks with curly braces. Blocks have a name, an optional label, and a body containing arguments and nested unlabeled blocks.

Some blocks can be defined multiple times.

Examples

Use the following pattern to create an unlabeled block.

alloy
BLOCK_NAME {
  // Block body can contain attributes and nested unlabeled blocks
  IDENTIFIER = EXPRESSION // Attribute

  NESTED_BLOCK_NAME {
    // Nested block body
  }
}

Use the following pattern to create a labeled block.

alloy
// Pattern for creating a labeled block:
BLOCK_NAME "BLOCK_LABEL" {
  // Block body can contain attributes and nested unlabeled blocks
  IDENTIFIER = EXPRESSION // Attribute

  NESTED_BLOCK_NAME {
    // Nested block body
  }
}

Block naming rules

The BLOCK_NAME must be a valid component name or a special block for configuring global settings in Alloy. If required, the BLOCK_LABEL must be a valid Alloy identifier wrapped in double quotes. Use the label to distinguish between multiple top-level blocks with the same name.

The following snippet defines a block named local.file with the label “token.” The block’s body sets filename to the content of the TOKEN_FILE_PATH environment variable using an expression. The is_secret attribute is set to true, marking the file content as sensitive.

alloy
local.file "token" {
  filename  = sys.env("TOKEN_FILE_PATH") // Use an expression to read from an env var.
  is_secret = true
}

Terminators

All block and attribute definitions end with a newline, which Alloy calls a terminator. A newline acts as a terminator when it follows any expression, ], ), or }. Alloy ignores other newlines, so you can add as many as you want.