A single-page web application containing both an IEEE 754 Encoder (for encoding a decimal value into its IEEE-754 single and double precision representation), and an IEEE 754 Decoder (for coverting a 32 or 64-bit hexidecimal representation into a decimal value).
The application works entirely in JavaScript; there is no need for a server.
You will need a modern browser, as the JavaScript code uses Uint8Array and friends.
This application incorporates Michael Mclaughlin's big.js library.