Overview
Introduction
MessagePack is the binary format behind Redis pub/sub payloads, msgpack-rpc, and plenty of caching and queueing systems that need JSON's flexibility without JSON's text overhead. This tool encodes JSON straight into it.
The result is shown as a hex dump so it stays copy-pasteable in the browser, ready to feed into a decoder, test fixture, or the matching MessagePack to JSON tool on this site.
What Is JSON to MessagePack Converter?
An encoder that walks a parsed JSON value and writes it out using MessagePack's type-tagged binary format, where a leading byte (or byte range) identifies the value's type and, for fixed-size types, its length.
It targets exactly the types JSON already has, nil, bool, integer, float, string, array, and map, and always picks the smallest MessagePack encoding that fits each value.
How JSON to MessagePack Converter Works
Each value is dispatched by its JavaScript type: null becomes the nil byte 0xc0, booleans become 0xc2/0xc3, safe integers are packed into the narrowest fixint or int8/16/32/64 format that holds them, and non-integer numbers become a float64.
Strings, arrays, and maps each check their encoded length against MessagePack's fixed-size thresholds (31 bytes for fixstr, 15 items for fixarray/fixmap) and fall back to the 8/16/32-bit length-prefixed variant only when needed.
When To Use JSON to MessagePack Converter
Use it when you need to hand-craft a MessagePack payload for a Redis command, an RPC test, or a wire-format fixture without writing a packer script.
It's also useful for understanding exactly how a given JSON value would be packed byte-for-byte before implementing MessagePack support in another language.
Often used alongside MessagePack to JSON Converter, JSON to Bencode Converter and JSON to UBJSON Converter.
Features
Advantages
- Always picks the smallest valid MessagePack encoding for each value, matching a real packer's output size.
- Runs entirely client-side, so no data leaves the browser during encoding.
- Produces output that decodes cleanly with the companion MessagePack to JSON tool for round-trip testing.
Limitations
- Never produces bin or ext type family bytes, since JSON has no source type that maps to them.
- Non-integer numbers always become float64, never the smaller float32 format, since JSON doesn't distinguish the two at parse time.
- Output is a hex dump, not a downloadable raw binary file.
Examples
Best Practices & Notes
Best Practices
- Round-trip through MessagePack to JSON after encoding to confirm the byte layout matches what your target system expects.
- Keep integers within the safe integer range when precision matters, since anything larger is truncated the same way JSON.parse would truncate it.
- Strip the spaces from the hex dump before feeding it to a system that expects raw bytes rather than a hex string.
Developer Notes
The encoder shares its ByteWriter/writeValue logic with the decoder in msgpack-core.ts, and deliberately mirrors real packer behavior by trying the smallest format first at every branch (fixint before int8, fixstr before str8) rather than always emitting a fixed-width encoding, which keeps output byte-identical to what a production msgpack library would produce for the same input.
JSON to MessagePack Converter Use Cases
- Building a MessagePack payload to send over a Redis or msgpack-rpc connection
- Creating binary test fixtures for a MessagePack decoder implementation
- Comparing encoded size against JSON or other binary formats for the same data
Common Mistakes
- Expecting a raw downloadable .msgpack file instead of a hex-encoded text dump.
- Assuming decimal numbers get the compact float32 format; they're always encoded as float64.
- Passing non-integer or out-of-range numbers and expecting lossless round-tripping beyond what float64 precision allows.
Tips
- Pair with MessagePack to JSON to verify a payload decodes back to the exact JSON you started with.
- For a text-based alternative with similar compactness goals, compare against JSON to Bencode.