Condition blocks

A condition block tests something and sends the message, unchanged, on its yes or no output. Use them to filter and branch. All condition blocks also have an error output for a test that could not be made. This page lists them as the blocks define them, then explains the values, paths and expressions they use.

Compare

Compares one property with a value.

Setting	Meaning	Default	Values
property	What is tested	msg.payload	a msg., flow., global. or sys. path
op	The comparison	eq	see the operators below
value	What it is compared with	empty	any value kind; not shown for true, false, null, empty, nempty

A missing property counts as null: gt 30 is then false. Errors: invalid_value (a bad pattern or operator), or the code of a value that could not be worked out.

Operators

Shared by Compare, Any / all of, Device state and Switch:

Operator	True when
eq, ne	Equal, not equal. A number and a number or numeric text compare as numbers ("5" equals 5, true counts as 1); anything else compares by content as JSON.
lt, le, gt, ge	Less, less or equal, greater, greater or equal. Numbers and numeric text as numbers; two texts alphabetically; any other mix is false.
contains	Text contains the value; an array has an equal element; an object has a key of that name
regex	Text (or a number as text) matches the pattern: case-sensitive, at most 64 characters
true, false	Exactly the boolean true / false (not 1, not "true")
null	Missing or null
empty, nempty	null, "", [] or {} / anything else
type	The type is number, string, boolean, array, object or null

Patterns cannot use lookahead, lookbehind or back-references; such a pattern is refused at deploy (regex_unsupported).

Any / all of

Up to 8 comparisons joined by “or” or “and”.

Setting	Meaning	Default	Values
mode	How the rows are joined	any	any (or), all (and)
items	One comparison per row: property, op, value	none	up to 8 rows

Rows are checked in order and checking stops once the answer is known. With no rows, any is false and all is true.

If / else

True when an expression is true.

Setting	Meaning	Values
expr	The expression	required, up to 512 characters

no when the result is false, null, 0, "" or not a number; an empty array or object counts as true. Errors: invalid_value (does not compile), type, div_zero, steps, regex, limit.

Example: msg.payload.temperature > 30 && flow.mode == "auto".

In range

Is a number between a minimum and a maximum, with optional hysteresis.

Setting	Meaning	Default	Values
property	The number	msg.payload	a path
min	Lower limit, inclusive; empty = none	empty	a number
max	Upper limit, inclusive; empty = none	empty	a number
hyst	How far past a limit the value must go before the answer changes	0	0 or more
key	A separate memory per value of this path	msg.originator (one per device)	a path

Once inside, the answer stays yes until the value drops below min − hyst or rises above max + hyst; once outside, it turns yes again only within min + hyst … max − hyst. Not a number: no, memory unchanged.

Device state

Tests a stored variable (flow., global.) or a platform value (sys.) instead of the message. The message only decides when the test is made.

Setting	Meaning	Default	Values
path	What is tested, e.g. flow.mode, global.persist:count	required	a sys., flow. or global. path
op	The comparison	eq	as above
value	What it is compared with	empty	any value kind

Changed

yes when a property differs from its value in the previous message of the same key; the first message of a key is yes.

Setting	Meaning	Default	Values
property	The value watched	msg.payload	a path
key	A separate last value per value of this path	msg.originator (one per device)	a path

Values compare as JSON text: 5 and "5" differ.

Not repeated

yes only if nothing with the same key went through yes within the period.

Setting	Meaning	Default	Values
Period (window_ms)	How long after a yes the key is held back	1 h	0 to 7 days; 0 lets everything through
key	Keys counted apart	msg.originator (one per device)	a path

Only a yes starts the period; with a 1-hour period a steady stream gives one yes an hour. Use it to stop repeating notifications.

Happened n times

yes when this message makes at least n messages of the same key within the period.

Setting	Meaning	Default	Values
n	How many times	3	1 to 1,000
Period (window_ms)	Sliding window	10 min	1 ms to 7 days
key	Keys counted apart	msg.originator (one per device)	a path
reset_on_yes	Start counting from zero after a yes	off	on, off

Memory of condition blocks

In range, Changed, Not repeated and Happened n times remember values per key. On Hermetry the key defaults to the message’s originator, so each device has its own memory; set key to msg.topic (or another path) to share or split it differently. Each block keeps at most 10,000 keys; beyond that the oldest is forgotten. The memory survives restarts. Deploying a change to the block’s settings starts its memory empty. See Counters, statistics and watchdogs.

Values, paths and expressions

Many settings take a value of one of these kinds:

Kind	Example	Meaning
Number, Text, Yes / no, JSON	30, "alarm", true, {"on": true}	A fixed value
Variable (path)	msg.payload.level, flow.limit, global.persist:site.max	Read when the block runs
Expression	msg.payload.a + msg.payload.b	Worked out for every message
Environment variable		A value of the environment
Current time		The time the message arrives

Paths

• msg.…: the message. Fields starting with _ belong to the engine and cannot be written; msg.msgType and msg.originator are read-only.
• flow.…: variables of this flow. global.…: variables shared by all flows of the organisation. Add persist: to use the persistent store (flow.persist:total). The first key starts with a letter or _ and has at most 32 letters, digits or _.
• sys.…: read-only platform values.
• Missing paths give null.

Expressions

Up to 512 characters, at most 10,000 evaluation steps.

Part	Available
Values	numbers, "text", true, false, null, [arrays], {objects}, paths
Operators	?: || && == != < <= > >= in + - * / % !
Number functions	abs, round(x, decimals), floor, ceil, min, max, clamp(x, lo, hi), sqrt, pow, number, int, fixed, sum, avg, and trigonometric and logarithmic functions (sin, cos, asin, rad, log10 …)
Text functions	string, len, lower, upper, trim, substr, replace, split, join, contains, starts, ends, matches
Other	keys, has, now, fmt_time, typeof, exists, default(x, fallback), empty

• == compares numbers numerically and everything else by type and value; < and > with null are false.
• Arithmetic on text fails with type, even on numeric text: write number(msg.payload).
• {{ expression }} in text settings (templates) inserts a value: Level {{ msg.payload.level }} %.