Prompt Variable Injector - Dynamic Template Interpolator
Real-world AI applications rarely use static prompts; they dynamically interpolate runtime variables (user queries, database rows, customer names) into template skeletons using mustache-style syntax like {{variable}}. Manually testing template interpolations with edge-case characters often causes broken prompt syntax. This utility provides an interactive playground for testing prompt templates and running batch variable substitutions.
When to Use This Tool
- Personalized Email & Messaging: Generate tailored outreach prompts containing recipient names, company profiles, and custom value propositions.
- Dynamic RAG Context Injection: Test how retrieved knowledge chunks render inside prompt templates before passing to LLMs.
- Batch Synthetic Data Generation: Interpolate product catalog attributes into generation prompts to produce bulk synthetic training data.
- Template Edge-Case Testing: Verify how prompt templates handle empty variables, special characters, and multi-line strings.
How to Use
- Draft Template: Write your prompt template using double curly brackets for variables (e.g. Hello {{name}}, analyze {{topic}}).
- Auto-Detect Variables: The tool automatically detects and lists all unique variable keys extracted from your template.
- Provide Variable Values: Type in values or paste JSON/CSV data arrays for batch variable processing.
- Copy Rendered Output: Review the live interpolated prompt and copy it with a single click.
Input & Output Example
Input:
Template: Translate {{source_text}} into {{target_lang}}.
Variables: source_text="안녕하세요", target_lang="English"
Output:
Translate 안녕하세요 into English.
Frequently Asked Questions (FAQ)
Q. What syntax is supported for variables?
A. Standard double curly braces {{variable}} (Mustache / Handlebars style) are supported, which is the universal standard across LangChain, LlamaIndex, and Promptfoo.
Q. Can I inject multi-line code blocks as a variable value?
A. Yes. Variable inputs safely handle multi-line strings, code blocks with backticks, and nested quotation marks without syntax corruption.
Q. Are my variable data values stored on a server?
A. No. All variable interpolation and template compilation execute purely in your local browser sandbox.
Engineering & Privacy Notes
- Compliant with standard Handlebars/Mustache interpolation principles.
- Runs completely offline in browser memory ensuring sensitive customer records remain private.
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