MessagePack to JSON

Paste a MessagePack blob as hex or base64 and decode it into readable, pretty-printed JSON. Field order and full uint64 precision are preserved, timestamps become ISO strings, and binary/ext payloads are shown safely. Runs entirely in your browser — no upload, no sign-up.

About this tool

Paste a MessagePack blob as hex or base64 and this tool decodes it into readable, pretty-printed JSON. MessagePack is a compact binary serialization format used in caches (Redis), network protocols, config blobs, and driver payloads — great for machines, hard to read by eye. This decoder turns those bytes back into JSON you can inspect.

Field and element order is preserved (MessagePack maps are ordered), and full uint64 precision is kept, so a 64-bit id is not silently rounded to a float. Choose the indent, or set it to 0 to minify to one line. Everything runs locally in your browser using WebAssembly; the bytes are never uploaded.

MessagePack has a few types JSON cannot hold natively, so they are shown by a small, documented convention:

Raw binary (bin) → a base64 (default) or hex string of the bytes.
Extension (ext) → { "$ext": <type>, "data": "<base64|hex>" }.
The reserved timestamp extension (type -1) → an RFC 3339 / ISO 8601 UTC string.
Non-string map keys (numbers, booleans, nil) → stringified keys.

Worked example

The hex blob 82a7636f6d70616374c3a6736368656d6100 is the canonical MessagePack sample { "compact": true, "schema": 0 }. With Input encoding set to hex and Indent set to 2, the result is:

{
  "compact": true,
  "schema": 0
}

Set Indent to 0 and the same input minifies to one line:

{"compact":true,"schema":0}

Limits and edge cases

Input is a hex or base64 string, not a file upload. To decode a .msgpack file, base64- or hex-encode it first (for example base64 file.msgpack) and paste the text.
Several MessagePack values concatenated back-to-back are returned as a JSON array, in order.
Non-finite floats (NaN, Infinity) are rendered as null, since JSON has no way to represent them.

FAQ

What input formats does this accept?

Paste the MessagePack bytes as a hex or base64 string. With Input encoding left on auto, the tool detects which one you pasted; force it with hex or base64 if the encoding is ambiguous. Hex input may include spaces, :, -, or , separators and 0x markers — they are ignored — so byte dumps paste cleanly.

How are binary and extension types handled?

JSON has no binary type, so raw bin values and unknown ext payloads are encoded as a string. Use the Binary / ext encoding option to pick base64 (default) or hex. An unknown extension becomes { "$ext": <type>, "data": "<encoded>" }, and the reserved timestamp extension (type -1) is decoded to an ISO 8601 UTC string like 2018-01-01T00:00:00Z.

Does it keep full precision for large integers?

Yes. A 64-bit unsigned integer such as 18446744073709551615 (u64::MAX) is preserved exactly instead of being rounded to a floating-point number. Map key order is preserved too, so the JSON reflects the original document structure.

Is my data uploaded anywhere?

No. The decoder is compiled to WebAssembly and runs entirely in your browser tab. The MessagePack bytes you paste never leave your device, and there is no sign-up or request to a server.

Developer & Automation Access

Run it from the terminal

Same engine as this page, headless — via the gizza CLI:

gizza tool msgpack-to-json "82a7636f6d70616374c3a6736368656d6100"

New to the CLI? Get gizza →

Open it by URL

Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:

https://gizza.ai/tools/msgpack-to-json/?input=82a7636f6d70616374c3a6736368656d6100&input_format=auto&indent=2&binary_format=base64

Machine-readable descriptor: tool.json — title + parameters JSON Schema for agents.