Prompt Template Formatter — Fill Variables in AI Prompt Templates

Reusing AI prompts with different inputs is a common workflow — the same prompt structure, but with different names, topics, or data each time. SimpleTools Prompt Template Formatter lets you define templates with {{variable}} placeholders and fill them instantly — no code, no server.

What Is a Prompt Template?

A prompt template is a reusable prompt structure with named placeholders that get replaced with actual values before sending to an LLM:

You are a professional email writer. Write a {{tone}} email to {{recipient_name}} 
about {{subject}}. The email should be approximately {{word_count}} words.
Include a clear call-to-action: {{call_to_action}}.

Variables: {{tone}}, {{recipient_name}}, {{subject}}, {{word_count}}, {{call_to_action}}

Fill in the values, and you get a complete, ready-to-use prompt.

Why Use Prompt Templates?

Consistency: Ensure the same prompt structure is used across all instances of a task — no variation in instructions between runs.

Efficiency: Write the prompt structure once, reuse it hundreds of times with different inputs.

Collaboration: Share template files with teammates; each person fills in their own variable values.

Testing: Use the same template with different variable values to test how LLMs respond to variations.

Version control: Templates are text files — they can be stored in Git alongside your codebase.

Features of the Template Formatter

• Auto-detect variables: Paste any template with {{variable_name}} syntax — variables are detected automatically
• Inline filling: Each detected variable gets its own input field — no manual search-and-replace
• Live preview: See the filled prompt update in real time as you type variable values
• Copy filled prompt: One-click copy of the complete prompt with all variables replaced
• Save templates: Export the template and variable values as a JSON file for later reuse
• Load saved templates: Import previously saved template files

Works Completely Offline

Prompt templates often contain proprietary business logic — the specific instructions that define how your AI product behaves. This is sensitive IP.

SimpleTools Prompt Template Formatter:

✅ Your templates and values never leave your browser
✅ Works offline — fill templates without internet
✅ No account needed
✅ No cloud sync — everything stays on your device

How It Works

The tool uses a simple JavaScript regex to detect template variables:

const variablePattern = /\{\{([a-zA-Z_][a-zA-Z0-9_]*)\}\}/g;
const variables = [...template.matchAll(variablePattern)]
  .map(match => match[1]);

Once variables are detected, an input form is generated. As you type values, a string replacement produces the filled prompt:

const filled = variables.reduce((text, varName) => 
  text.replaceAll(`{{${varName}}}`, values[varName] || ''), 
  template
);

All of this runs in the browser — no round-trips to a server.

How to Use the Prompt Template Formatter

1. Visit simpletools.one/prompt-template-formatter
2. Paste your prompt template with {{variable_name}} placeholders
3. Variable input fields appear automatically below the template
4. Fill in each variable’s value
5. See the completed prompt in the preview panel (updates live)
6. Click Copy Prompt to copy to clipboard
7. Save the template and values as JSON for reuse

Template Syntax

The tool supports the {{variable_name}} double-brace syntax, which is also used by popular templating systems like:

• LangChain prompt templates
• LlamaIndex prompt templates
• Jinja2 (with minor syntax difference: {{ variable }})
• Handlebars.js

This makes it straightforward to use the tool with existing templates from popular AI frameworks.

Real-World Template Examples

Content generation:

Write a {{content_type}} about {{topic}} for {{target_audience}}. 
Length: {{word_count}} words. Tone: {{tone}}.

Code review:

Review the following {{language}} code for {{review_focus}}:

```{{language}}
{{code}}

Focus on {{specific_concerns}}. Provide feedback in {{feedback_format}} format.

**Customer support**:

You are a support agent for {{company_name}}. A customer says: “{{customer_message}}” Respond helpfully and {{tone}}. Reference the following policy: {{policy_snippet}}

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Try the Prompt Template Formatter at [simpletools.one/prompt-template-formatter](https://simpletools.one/prompt-template-formatter) — private, instant, and free.