Data transform blocks

Transform blocks change the message and send it on. They are how you rename keys, compute values, build texts and decode raw device data before Save telemetry. Each has an out output and an error output. None of them keeps state.

Change

Sets, edits, deletes or moves properties of the message and of flow or global variables, in steps done from top to bottom.

Setting	Meaning	Values
ops	The steps	up to 16 rows

Each step:

op	Does	Fields
set	Writes a value; missing parents are created	path, value (any value kind)
change	Replaces every occurrence of from with to in text; non-text is left alone	path, from, to, regex (a pattern of at most 64 characters)
delete	Removes the property or variable	path
move	Copies to the path in to, then deletes the original. The editor does not show the to field yet, so use set and delete instead.	path, to
copy keys	Copies every top-level key of the object at path whose whole name matches Keys matching into To object	path, Keys matching, To object
delete keys	Deletes every top-level key whose whole name matches	path, Keys matching

Paths are msg., flow. or global. paths (flow.persist:x for the persistent store). Engine fields (_…), msg.msgType and msg.originator cannot be written. Errors: invalid_value with invalid_path, read_only, invalid_key, limit (variable store full) or bad pattern; steps before the failing one are already applied.

Example: rename a device’s key before saving: step 1 set msg.payload.temperature to the path msg.payload.tmp; step 2 delete msg.payload.tmp.

Calculate

Works out an expression and writes the result.

Setting	Meaning	Default	Values
expr	The expression	required	up to 512 characters
target	Where the result goes	msg.payload	a msg., flow. or global. path

7 / 2 is 3.5; + joins text when either side is text; arithmetic on null or any text (even "21.5") fails with type: convert with number(). Errors: invalid_value, type, div_zero, steps, limit. See Condition blocks for the functions.

Examples: round(msg.payload.temperature * 1.8 + 32, 1); 10 * log10(msg.payload.ratio); clamp(msg.payload.level, 0, 100).

Scale

Maps a number linearly from one range to another, in place.

Setting	Meaning	Default	Values
property	The number	msg.payload	a path
in_min, in_max	The input range	0, 4095	numbers, not equal
out_min, out_max	The output range	0, 100	numbers
mode	Outside the output range	clamp	clamp (limit), wrap (wrap around), free (leave)
round	Decimal places	none	0 to 10

Formula: out_min + (value − in_min) × (out_max − out_min) / (in_max − in_min). Numeric text and true/false (1/0) count as numbers. Error invalid_value (“not a number”, or an empty input range).

Template

Builds text, or a JSON value, from {{ expression }} placeholders.

Setting	Meaning	Default	Values
template	The text	{{ msg.payload }}	up to 4,096 characters
target	Where the result goes	msg.payload	a msg., flow. or global. path
format	text, or json (the result is parsed as JSON)	text	text, json

null becomes empty, objects and arrays are written as JSON. For JSON output, put text placeholders in quotes yourself: {"temp": {{ msg.payload }}, "unit": "{{ flow.unit }}"}. The result is at most 64 KB of text.

JSON

Turns JSON text into a value, or a value into JSON text, in place.

Setting	Meaning	Default	Values
mode	auto (parse text, pass the rest), parse, stringify	auto
property	The property	msg.payload	a path

Errors: invalid_value “not JSON: …” or “not a string”.

CSV

CSV text to records, or records to CSV text, in place.

Setting	Meaning	Default	Values
mode	auto, decode, encode	auto
property	The property	msg.payload	a path
sep	Field separator	comma	comma, semicolon, tab, pipe
header	Decode: the first line has the names. Encode: write a header line	off	on, off
columns	Column names, comma-separated	empty	up to 256 characters
numbers	Decode: number-like fields become numbers	off	on, off
output	Decode: one message with all records (array) or one per record (rows)	array	array, rows

Quoting follows RFC 4180. Error queue_full over 10,000 lines or records.

XML

XML text to an object, or an object to XML text.

Setting	Meaning	Default
Mode	parse, build, or auto
Property	Where the conversion happens	msg.payload
Attribute prefix	Prefix of attribute keys	@
Text key	Key of text next to child elements	#text
Arrays / array elements	Which elements are always arrays
Numbers	Numeric text becomes numbers	off
Select	Keep only one element path, e.g. soap:Envelope/soap:Body/*/m:Price
Root, Declaration	Building: the root element name, the <?xml …?> line
Max bytes	Largest input	64 KiB (1 to 256 KiB)

A document with <!DOCTYPE is refused. At most 10,000 elements, 64 attributes per element, 128 characters per name. Errors: parse_error, dtd_refused, too_large, too_deep, bad_name, no_root.

Hex and Base64

Encode a property as hex (two lower-case digits per byte) or base64 text, or decode it back.

Setting	Meaning	Default	Values
mode	Which way	auto	auto, encode, decode
property	The property	msg.payload	a msg., flow. or global. path

In auto, text that looks like hex (or base64) is decoded and everything else encoded; short words such as test or digits such as 2024 are valid base64 or hex too, so choose encode or decode when you know the direction. Hex decoding ignores spaces and colons.

Bytes

Reads named numbers from binary data, or builds binary data from numbers.

Setting	Meaning	Default	Values
mode	Read or build	decode	decode, encode
fields	One row per field	empty	up to 16 rows

Each field:

Field	Meaning	Default	Values
name	Key in the result	required	a letter or _ first, up to 32 characters
offset	First byte, from 0	0	0 to 4,095
type	Size and kind	u16	u8, i8, u16, i16, u32, i32, f32
le	Little endian	off (big endian)	on, off
bits	A bit range start:length	whole field	e.g. 0:1, 4:3
scale	Decode: × scale; encode: ÷ scale	1	a number

Decode reads hex text (spaces and colons ignored) or an array of byte values in msg.payload and writes { name: value }. Encode writes hex text. Error invalid_value when the data is not hex or a field lies beyond its end.

Example: a raw payload 00d7ff9c with temp (offset 0, i16, scale 0.1) and pressure (offset 2, i16) gives { "temp": 21.5, "pressure": -100 }.

Decoding raw device data

A device that sends binary data arrives with the single key raw (base64 for binary). A typical decoder in the root flow, before Save telemetry:

Switch (msg.payload.raw nempty) → Change: set msg.payload to the path msg.payload.raw
  → Base64 (decode) → Hex (encode) → Bytes (decode fields) → Save telemetry

Check the result with Test before you deploy. For LoRaWAN devices, use codecs instead; see Codecs overview. For anything the blocks cannot express, use The script block.