What chunk sizes are available?

You can choose presets of 256, 512, 1 024, 4 096, or 8 192 characters, or enter a custom size. Smaller chunks suit message queues with payload limits; larger chunks reduce overhead.

What output formats are produced?

JSON array format outputs a JSON array of objects with index, total, and data fields. Line format outputs one chunk per line as "b64chunk: / : ", useful for line-oriented transports.

Can I upload a file directly?

Yes. Switch to "Upload file" mode, drop any file up to 10 MB, and the tool encodes it to Base64 then splits it automatically.

Is my data uploaded to a server?

No. All encoding and chunking happens entirely in your browser. Nothing is sent anywhere.

How do I rebuild the original string from chunks?

Paste the chunked output into the Base64 Reassembler tool. It validates the sequence and rebuilds the original Base64 string.

What is the difference between chunk size and the decoded file size?

Chunk size is measured in Base64 characters, not bytes. Because Base64 encodes 3 bytes as 4 characters, a 1 024-character chunk carries approximately 768 bytes of decoded data. Keep this in mind when sizing chunks against a transport limit measured in bytes.

Can I upload any file type?

Yes. The tool accepts any file up to 10 MB. It reads the raw bytes, encodes them as standard Base64, then chunks the resulting string. The MIME type is not relevant to the chunking step.

How do I reassemble the chunks on the receiving end?

Paste the JSON or line-format output into the Base64 Reassembler tool. Alternatively, sort the chunks by index and concatenate the data fields — the result is the complete original Base64 string.

What happens if the input is not valid Base64?

The tool checks the alphabet before chunking and shows a clear error if the input contains characters outside the Base64 set (A–Z, a–z, 0–9, +, /, =, - and _). Fix or re-encode the source data and retry.

Base64 Chunker

Paste a Base64 string or upload a file, choose a chunk size, and get a validated numbered chunk set ready for reassembly — with zero server uploads.

Updated June 2026

Files never leave your browser

Output format

Chunk size

Base64 string to split

All processing happens in your browser. Nothing is uploaded.

How to use Base64 Chunker

The Base64 Chunker splits any Base64-encoded string — or any file you upload — into fixed-size numbered chunks with embedded sequence metadata. Each chunk carries its index and total so a downstream consumer can detect gaps, reassemble out-of-order arrivals, or apply per-chunk integrity checks without needing a side-channel manifest. Chunked output is available as a JSON array or a compact line format, both fully parseable by the companion Base64 Reassembler. All encoding and splitting happen in your browser; files never leave your device.

Paste a Base64 string into the input field, or switch to "Upload file" and drop any file up to 10 MB.
Select the output format — "JSON array" for structured consumers or "Line format" for line-oriented transports.
Choose a chunk size preset (256 – 8 192 characters) or click "Custom" and enter your own size.
Click "Split into chunks" to produce the numbered chunk set.
Review the stat panel (total chars, chunk count, last-chunk size), then copy the output or download it as a file.
Paste the output into the Base64 Reassembler to verify sequence integrity before sending.

Your data never leaves your device — 100% private processing.

Why chunk Base64 strings for transport?

Many messaging systems impose strict per-message payload limits — MQTT brokers default to 256 KB, SMS gateways typically cap at a few hundred bytes, and some HTTP APIs enforce request body limits to protect against oversized inputs. When a file or binary blob needs to pass through one of these transports, it is first encoded to Base64 (which makes it text-safe at a 33 % size cost) then split into segments small enough for the channel. Each segment carries a sequence number and total so the receiver can detect missing parts, reassemble fragments arriving out of order, and refuse to process a partially-delivered payload. This tool automates the splitting and numbering step, producing output in either a JSON format that structured consumers can parse directly or a compact line format convenient for plain-text transports.

Common chunk size choices by transport type
Transport	Suggested chunk size	Reason
MQTT (default broker limit)	512 – 4 096 chars	Typical broker max is 256 KB; large payloads need splitting
SMS / messaging gateway	256 chars	SMS segment is 160 chars; short chunks keep parts under limit
HTTP multipart upload	4 096 – 8 192 chars	Large chunks reduce part count while staying under API limits
WebSocket message	1 024 – 4 096 chars	Avoids buffering large frames on low-memory devices
OTA firmware update (IoT)	256 – 1 024 chars	Flash write pages are typically 256 – 512 bytes

JSON vs line format: choosing the right output

The JSON array format encodes each chunk as an object with three keys — "index" (1-based position), "total" (overall chunk count), and "data" (the Base64 characters for this segment). This structure is ideal for programmatic consumers: any JSON parser can iterate the array, access named fields, and add extra fields (like a per-chunk checksum) without breaking parsers that ignore unknown keys. The line format writes one chunk per line as "b64chunk:<index>/<total>:<data>", which is more compact and suits line-oriented consumers such as shell scripts, log parsers, and serial-port transports. Both formats carry full sequence information so the Base64 Reassembler can validate and rebuild the original string from either one. Use JSON when the receiver already works with structured data, and line format when you need minimal overhead or human-readable progress.

Worked examples

Split a Base64 PNG for MQTT transport

Inputs: 4 000-char Base64 PNG, chunk size 512

Result: 8 chunks · 512 chars each (last chunk may be shorter)

Chunk a PDF for multi-part HTTP upload

Inputs: 20 000-char PDF Base64, chunk size 4 096

Result: 5 chunks · JSON array with index 1–5, total 5

Glossary

Base64 chunk: A fixed-size substring of a Base64 string, tagged with a sequence index and total count so receivers can validate completeness and order.
Sequence metadata: The index and total fields attached to each chunk — they are the minimal information needed to detect missing or duplicate parts and reassemble in order.
JSON array format: An output format where each chunk is a JSON object with "index", "total", and "data" fields, wrapped in a top-level JSON array.
Line format: A compact output format writing one chunk per line as "b64chunk:<index>/<total>:<data>", suitable for line-oriented transports and shell scripts.
Chunk size: The maximum number of Base64 characters (not bytes) in each segment. The last chunk may be shorter if the total length is not evenly divisible.

Frequently Asked Questions

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Why use Base64 Chunker?

Split Base64 strings of any size into precisely sized numbered chunks in one click
Choose from presets (256, 512, 1 024, 4 096, 8 192 chars) or enter a custom chunk size
JSON array and line-format outputs suit different downstream consumers and transports
Upload any file up to 10 MB — the tool encodes it to Base64 and chunks it automatically
Companion tool Base64 Reassembler validates and rebuilds the original string end-to-end

Common use cases

Break a large Base64-encoded PDF into chunks that fit within an SMS, push notification, or IoT MQTT message limit
Split a Base64 image payload into parts for a multi-step wizard that submits one chunk per HTTP request
Generate a numbered chunk set to test a queue consumer's ability to handle out-of-order delivery
Divide a firmware image encoded as Base64 into fixed-size OTA update segments for embedded devices

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