Template Variables

Promptmark templates use {{variable}} syntax to create fill-in-the-blank prompts. This page documents the complete specification.

Syntax

{{name}}                              Simple variable (string, required)
{{name:type}}                         Typed variable (required)
{{name:type:default}}                 Typed with default (optional)
{{name:enum:opt1,opt2,opt3}}          Enum options (required)
{{name:enum:opt1,opt2,opt3:default}}  Enum with default (optional)

Variable Names

Variable names must follow these rules:

• Must start with a letter (a-z, A-Z)
• Can contain letters, digits (0-9), and underscores (_)
• Cannot start with an underscore

Valid: name, first_name, user123, Topic Invalid: _reserved, 1st, my-var

Types

If no type is specified, the variable defaults to string.

Default Values

A variable with a default value is optional — it can be left empty during rendering and the default will be used.

A variable without a default is required — rendering will use the variable name as a placeholder if no value is provided.

{{name}}              → Required (no default)
{{name:string:World}} → Optional (defaults to "World")
{{active:bool:true}}  → Optional (defaults to "true")

Default values have a maximum length of 500 characters.

Enum Variables

Enums define a fixed set of options:

{{style:enum:formal,casual,technical}}

Options are separated by commas. Whitespace around options is trimmed automatically:

{{size:enum:small, medium, large}}  → ["small", "medium", "large"]

Enum with Default

The default value is specified after the last colon:

{{style:enum:formal,casual,technical:casual}}

The default must be one of the defined options. If the default doesn’t match any option, it’s ignored.

Rendering Behavior

During rendering, variables are resolved in this priority order:

1. Provided value — Value explicitly passed for this variable
2. Default value — If the variable has a default and no value was provided
3. Unresolved — The {{placeholder}} text remains unchanged

Duplicate Variables

If a variable name appears multiple times in a template, it’s treated as a single variable. All occurrences are replaced with the same value:

Dear {{name}}, Thank you {{name}} for your inquiry.
→ Dear Alice, Thank you Alice for your inquiry.

Type Validation

Types are validated on input, not on output. During rendering:

• number — Value must parse as a valid number (integers, decimals, scientific notation like 1e10)
• boolean — Value must be true, false, 1, or 0 (case-insensitive)
• enum — Value must exactly match one option (case-sensitive)
• string / text — No validation

Empty strings (after trimming whitespace) are treated as “not provided.”

Examples

Code Review Template

Review this {{language:enum:Python,JavaScript,Go,Rust}} code for
{{focus:enum:bugs,performance,security,readability:bugs}}:

{{code:text}}

Provide {{detail:enum:brief,detailed:detailed}} feedback.

Variables:

• language — Required enum, 4 options
• focus — Optional enum, defaults to “bugs”
• code — Required multi-line text
• detail — Optional enum, defaults to “detailed”

Email Generator

Write a {{tone:enum:formal,casual,professional:professional}} email
to {{recipient}} about {{subject}}.

Additional context: {{context:text:None provided}}

Variables:

• tone — Optional enum, defaults to “professional”
• recipient — Required string
• subject — Required string
• context — Optional text, defaults to “None provided”

MCP Integration

Template variables work with MCP tools:

• get_prompt_schema — Returns all variables with types, options, and defaults
• validate_prompt_inputs — Validates variable values before rendering
• render_prompt — Substitutes variables and returns the rendered text

// get_prompt_schema response
{
  "variables": [
    {
      "name": "language",
      "type": "enum",
      "required": true,
      "options": ["Python", "JavaScript", "Go", "Rust"]
    },
    {
      "name": "code",
      "type": "text",
      "required": true
    }
  ]
}

Limits