What UBJSON container format does this decoder read?

It reads UBJSON's basic container format, where each array/object element carries its own type marker, the same format the site's JSON to UBJSON Converter produces. The optimized (strongly-typed, fixed-length) container variant isn't handled.

Why does this tool take a hex string rather than a binary file?

Browsers can't easily accept or display raw binary as text, so a hex dump (two characters per byte) is the practical input format for a browser-based decoder; it accepts exactly the format the companion encoder outputs.

How does this decoder handle UBJSON's different integer types?

It reads the type marker for each value (int8, uint8, int16, int32, int64, or float64) and converts it directly to the corresponding JSON number, regardless of which specific integer width the encoder originally chose.

What happens if the hex input is truncated or has an unknown type marker?

The decoder reports an error naming what it expected and where, since a truncated byte sequence or an unrecognized type marker means the rest of the input can no longer be reliably interpreted.

UBJSON to JSON Converter - Decode UBJSON Online

Overview

Introduction

UBJSON's binary, type-tagged bytes are efficient for machines to parse but opaque to read directly, especially when you're debugging an embedded system's output or a custom UBJSON packer.

This tool decodes hex-encoded UBJSON back into readable JSON so you can verify what a given byte sequence actually represents.

What Is UBJSON to JSON Converter?

A UBJSON decoder that reads a hex-encoded byte sequence's type markers (S for string, various integer types, [ / { for containers) and reconstructs the equivalent JSON value.

It targets UBJSON's basic container format, matching the output of the site's JSON to UBJSON Converter, rather than the optimized (strongly-typed) container variant.

How UBJSON to JSON Converter Works

The decoder converts the hex text into raw bytes, then reads one type marker at a time, dispatching to the right decoding logic (fixed-width read for numbers, length-prefixed read for strings, recursive element reads for [ arrays and { objects) based on that marker.

Container types are recognized by their ] or } terminator byte, so the decoder knows exactly when to stop reading elements and return to the parent container.

When To Use UBJSON to JSON Converter

Use it when you have a UBJSON hex dump, from an embedded system, a game save file format, or the JSON to UBJSON Converter, and need to see what JSON value it decodes to.

It's also useful for verifying a custom UBJSON encoder's output is correct by comparing the decoded JSON against what you expected.

Often used alongside JSON to UBJSON Converter, BSON to JSON Converter and MessagePack to JSON Converter.

Features

Advantages

Decodes every integer width UBJSON defines (int8 through int64) transparently into a single JSON number type.
Reports a specific error location for malformed or truncated input instead of failing silently.
Runs entirely client-side, so no data being decoded ever leaves the browser.

Limitations

Only reads UBJSON's basic container format, not the optimized (strongly-typed, fixed-length) variant some encoders produce.
Expects hex-encoded input, not an uploaded raw binary .ubj file.

Examples

Decoding a small object

Input

7b 69 04 6e 61 6d 65 53 69 03 41 64 61 69 03 61 67 65 69 1e 69 06 61 63 74 69 76 65 54 7d

Output

{
  "name": "Ada",
  "age": 30,
  "active": true
}

The { starts an object; each S-string key and its typed value (string, int8, boolean) are read in sequence until the closing }.

Invalid UBJSON

Input

7b 69 04 6e 61 6d 65

Output

Invalid UBJSON: unexpected end of input while reading a value

A byte sequence that ends mid-value (here, missing the string's payload) is rejected with a description of the problem.

Best Practices & Notes

Best Practices

Use the exact hex output from JSON to UBJSON Converter when testing the pair, to avoid an invalid or unsupported type marker.
Strip formatting like 0x prefixes or commas from a copied hex dump before pasting, the decoder expects plain space-separated hex pairs.
If a document from another UBJSON implementation fails to decode, check whether it uses the optimized container format, which this decoder doesn't read.

Developer Notes

The decoder advances a byte cursor strictly according to each type marker's known width or explicit length prefix (never scanning for delimiters), which mirrors how the basic UBJSON container format is actually structured: fully self-describing byte-by-byte with no separate index or schema to consult.

UBJSON to JSON Converter Use Cases

Inspecting UBJSON output from an embedded system or game save format as readable JSON
Verifying a custom UBJSON encoder's output round-trips to the expected JSON
Debugging a UBJSON-based binary protocol by decoding captured byte sequences

Common Mistakes

Pasting an optimized-format UBJSON container's bytes, which use a different, unsupported layout.
Including non-hex formatting characters in the pasted input, which breaks the byte-pair parsing.
Expecting a raw binary .ubj file upload to work directly instead of its hex representation.

Tips

Pair with JSON to UBJSON afterward to confirm decoding round-trips correctly.
When a decode fails partway through, check the byte immediately before the failure point first, most errors trace back to a wrong type marker or length prefix there.

UBJSON to JSON Converter