Field Types & Variable Syntax

PromptRenderer processes three kinds of template expressions. All expressions use double-curly-brace ({{ }}) delimiters.

Simple Variable Substitution

{{variableName}}

The value of variableName from the variables map is stringified and inserted at that position.

Value type	Output
string	Inserted as-is
number	Converted with String()
boolean	"true" or "false"
object / array	JSON.stringify() output
null / undefined	Empty string ""

Example:

Template: "Summarize {{topic}} for {{audience}}."
Variables: { topic: "quantum computing", audience: "high school students" }
Output:   "Summarize quantum computing for high school students."

Escaping Braces

To include a literal {{ in the output, prefix it with a backslash:

Template: "Use the syntax \{{variable}} in your templates."
Output:   "Use the syntax {{variable}} in your templates."

Missing Variables

By default (strict: true), an unresolved variable is left as the raw {{variableName}} token in the output. Strict mode does not throw on simple substitution failures — use requiredVariables for that.

renderer.render('Hello {{name}}', {}, { strict: false });
// → 'Hello {{name}}'

renderer.render('Hello {{name}}', {}, {
  requiredVariables: ['name'],  // throws RendererError if name is missing
});

Conditional Blocks: {{#if}}

{{#if conditionVariable}}
  content rendered when conditionVariable is truthy
{{/if}}

The block is rendered only when conditionVariable is truthy. Truthiness follows these rules:

Value	Truthy?
Non-empty string	Yes
Non-zero number	Yes
true	Yes
Non-empty array	Yes
Non-empty object	Yes
false	No
"" (empty string)	No
0	No
null / undefined	No
[] (empty array)	No

Example:

{{#if priority}}
This ticket is classified as {{priority}} priority.
{{/if}}

With { priority: "high" } → renders the block. With { priority: "" } or omitted → renders nothing.

Nested {{#if}} blocks are not supported in the current renderer. Compose conditions in your variable map instead.

Iteration Blocks: {{#each}}

{{#each arrayVariable}}
  content for each item
{{/each}}

Iterates over an array. Two modes:

Object Items

When each array element is an object, its keys become available as variables inside the block:

{{#each steps}}
Step {{number}}: {{description}}
{{/each}}

renderer.render(template, {
  steps: [
    { number: 1, description: 'Install dependencies' },
    { number: 2, description: 'Configure environment' },
  ],
});
// Step 1: Install dependencies
// Step 2: Configure environment

Primitive Items

When each element is a string or number, use {{this}} to reference the current item:

Tools available: {{#each tools}}{{this}}, {{/each}}

renderer.render(template, { tools: ['search', 'calculator', 'weather'] });
// Tools available: search, calculator, weather,

Empty or Missing Arrays

If the variable is absent, null, or an empty array, the {{#each}} block renders as an empty string — no error is thrown regardless of strict mode.

Variable Types (PromptVariableType)

When declaring variables in a promptVariableType minion, you specify one of:

Type	Description	Example value
string	Free text	"quantum computing"
number	Numeric value	42
boolean	True/false flag	true
array	Ordered list	["a", "b", "c"]
object	Key-value map	{ "key": "value" }

Variable Declaration Fields

A PromptVariable object has these fields:

interface PromptVariable {
  name: string;            // e.g. "audience"
  type: PromptVariableType;
  description?: string;   // Human-readable explanation
  required: boolean;       // Enforced via requiredVariables option
  defaultValue?: unknown;  // Not auto-applied by renderer; use in your calling code
  example?: string;        // Illustrative example for documentation
}

Variable declarations are stored separately as promptVariableType minions linked to the template, not automatically parsed from the template content. The renderer itself only reads the variables map you pass at render time.

Extracting Variables from a Template

PromptRenderer.extractVariables scans a template string and returns all referenced variable names:

const renderer = new PromptRenderer();
const names = renderer.extractVariables(
  'Write about {{topic}} for {{audience}}. {{#if formal}}Use formal language.{{/if}}'
);
// → ['topic', 'audience', 'formal']

This is used internally by PromptExporter.toLangChain to populate inputVariables.

Rendering Options Reference

renderer.render(template, variables, {
  strict?: boolean;            // Default: true. Controls whether unknown variables are left as tokens.
  requiredVariables?: string[]; // Names that must be present; throws RendererError if missing.
});

RendererError exposes a missingVariables array for programmatic handling:

import { RendererError } from '@minions-prompts/sdk';

try {
  renderer.render('Hello {{name}}', {}, { requiredVariables: ['name'] });
} catch (err) {
  if (err instanceof RendererError) {
    console.error('Missing:', err.missingVariables); // ['name']
  }
}