How to use the JSON Template Engine
Use JSON templates with dynamic placeholders:
1
Paste your JSON template
Enter a valid JSON string structure natively using double curly braces (e.g., `{{apiUrl}}`) anywhere inside the object.
2
Identify variables
The engine automatically parses your template and lists all detected unique `{{variables}}` in the editor panel.
3
Input substitution values
Type the exact strings you want injected into the parsed input fields. The engine applies them directly to the template.
4
Fill and export
Click 'Fill Template' to replace all occurrences. The tool validates the result as standardized JSON for safe copying.
When to use this tool
Use this when you need to generate multiple JSON variants from a template:
- →Populating identical Postman or Insomnia JSON request bodies with different environment variable values
- →Generating multi-environment (dev, staging, prod) JSON configuration definitions from a unified master template
- →Injecting dynamic user IDs, authentication tokens, and timestamps into automated webhook payloads
- →Creating parameterized ElasticSearch or MongoDB query payloads to paste into a database runner
- →Testing JSON parser behavior in Python or Java by injecting extreme or edge-case string values
Frequently asked questions
Q:How does the template parser identify variables?
The tool utilizes a regex pattern to parse any string enclosed perfectly in double curly braces, like {{myKey}} or {{123}}, automatically rendering an input field for it.
Q:Can placeholders be used deeply nested inside JSON values?
Yes. You can place the substitution variables anywhere inside JSON strings, including nested property values, deep arrays, or concatenated inside URLs like "https://{{domain}}/api".
Q:How do I safely use the output in backend code?
The tool dynamically replaces the string literals and then returns the output as valid JSON text. Simply copy the JSON and parse it in your application. Ensure your injected values don't break JSON syntax (e.g. injecting unescaped quotes).
Q:What if I have multiple identical variables in the template?
The engine de-duplicates detected variables in the UI. Inputting a value once will bulk-replace every identical {{variable}} occurrence across the entire JSON tree.
Q:Are my API templates sent to a server?
Completely private. Templating and regex variable substitution operate directly in your browser without any server connectivity, keeping your secrets entirely secure.