JSON Formatter
Format, minify and validate JSON without changing large integers, number notation, key order or string escapes. Import files and locate syntax errors.
HMAC calculator
Calculate HMAC-SHA-256, SHA-384 or SHA-512 using a text or hexadecimal key, useful for checking API signature inputs.
Advanced options
Updates as you type or change an option
About this tool
Debug API signatures by supplying the exact message your API expects. The tool does not sort parameters, join fields or append a newline.
How to use
Select an algorithm and key format, then enter the message and secret key. Text keys use UTF-8; hexadecimal keys decode each pair of digits into one byte. Changing any input recalculates the result.
The output is lowercase hexadecimal. The tool does not sort parameters, join fields or append newlines, so prepare the exact message required by your API. Message limit: 2 MiB; key limit: 64 KiB. Plain HTTP supports SHA-256.
A blank message does not generate an initial result. Enter a key to calculate a signature. To test empty values deliberately, enable the empty-key option in Advanced or use the explicit empty-message action; these are separate choices.
Common questions
Is text key 6162 the same as hexadecimal key 6162?
No. Text mode uses four UTF-8 characters. Hex mode uses the two bytes 0x61 and 0x62, equivalent to the text ab. Choose the representation specified by your API.
Why does my HMAC differ from the API signature?
Check the algorithm, key representation and exact message, including newlines. Output is hexadecimal, not Base64. The tool does not build the API’s signing string or transmit the message and key.
How can I test an empty message or key?
Advanced provides separate controls: choose the empty-message action for the message, and enable the empty-key option for a blank key. Leaving a field blank alone does not request both.
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