Action blocks

Action blocks do something: call another system, publish a message, store a variable, start a timer, hand the message to another flow, or write a log line. The device, alarm and notification actions are on their own pages: IoT data blocks and Alarm, command and notify blocks.

Common behaviour of outbound blocks

HTTP request, MQTT out and Webhook share these rules:

Topic	Behaviour
Risk	External: a deploy that contains one asks for a confirmation
Retries	Only transient failures retry; 3 attempts by default (retry_* settings), at most 5, with an exponential back-off from 1 s
Idempotency	Every attempt of one message carries the same key (X-Idempotency-Key, or the MQTT 5 user property idempotency-key), also after a crash or a replay, so a receiver can deduplicate
Delivery	At least once
Breaker	A block whose calls keep failing pauses its calls for a while (circuit_open)
Late messages	late: skip (default; the message stops, counted as Too old) or send (a data feed that must also get the backlog after an outage)
Tests	A test run sends nothing and reports what it would have sent
Order	HTTP request and MQTT out calls run separately from the run that made them: the device’s next message does not wait for the answer, and the order of messages after the call is not guaranteed
Addresses	Private and internal addresses are refused (ssrf_blocked)

HTTP request

Calls an HTTP endpoint and puts the answer into the message. Scheme, host, port, authentication and TLS come only from the endpoint connection, never from the message. See Connections and secrets.

Setting	Meaning	Default	Values
endpoint	The HTTP endpoint connection	required
host	Another host the endpoint allows	empty	a template; must match the endpoint’s allowed hosts
method	HTTP method	GET	GET, POST, PUT, PATCH, DELETE, HEAD
path	Appended to the endpoint’s base path	empty	a template, 1,024 characters
query	Query parameters	none	up to 16 rows
headers	Extra headers	none	up to 16 rows; Host, Authorization, Cookie, Proxy-*, Content-Length, X-Idempotency-Key and hop-by-hop headers are refused
body	What is sent	payload	payload, template, none (hidden for GET, HEAD, DELETE)
template	The body template	empty	up to 4,096 characters
template_format	How {{ }} values are written	text	text, json (each value as a JSON value; the body must be JSON)
timeout_ms	Time per attempt	10,000	1,000 to 30,000
parse	How the answer is read	auto	auto, json, text
max_bytes	Largest answer	64 KiB	1 to 256 KiB
response_headers	Answer headers kept in msg.metadata.headers	all	all, list, none (at most 32 headers, 8 KiB)
max_parallel	Calls in flight for this block	0 (no cap)	0 to 64
inline	Keep the call inside the run, so the device’s next message waits for the answer (the deploy warns)	off	on, off
retry_*	Attempts and back-off	3, from 1 s
late	See above	skip	skip, send

Outputs:

• out: status below 400. msg.payload is the body, msg.statusCode, msg.contentType, msg.metadata.headers. Redirects are not followed.
• error: http_status (400 or above, body in msg.payload), timeout, connect, tls, ssrf_blocked, too_large, invalid_json, invalid_value, oauth_failed, function_error, circuit_open, limit. msg.error.attempts says how many attempts were made.

Retried: timeouts, connection failures and HTTP 408, 425, 429 (honouring Retry-After), 500, 502, 503, 504.

For a JSON body built from values, use template_format: json and leave the placeholders unquoted: {"name": {{ msg.payload.name }}, "n": {{ msg.payload.n }}}.

HTTP response

Answers the caller of a synchronous Webhook trigger (reply: response). The first response of a run wins.

Setting	Meaning	Default	Values
status	HTTP status (msg.statusCode overrides it)	200	100 to 599
headers	Response headers	none	content-type, cache-control, location (3xx), x-* (not x-forwarded-*)
body	What is sent	payload	payload, template, none
template	Body template	empty	up to 4,096 characters
max_bytes	Largest body	256 KiB	at most 256 KiB

Errors: no_reply_pending, reply_sent, limit. Without a response the caller gets 204; after the hook’s timeout, 504.

MQTT out

Publishes the payload to a topic on your broker, then passes the message on. Text is sent as text, anything else as JSON.

Setting	Meaning	Default	Values
broker	The MQTT broker connection	required
topic	The topic	{{ msg.topic }}	a template, 256 characters; a leading ~/ is the broker’s topic prefix
qos	Delivery guarantee	0	0, 1, 2
retain	Ask the broker to keep the message	off	on, off
timeout_ms	Time for the acknowledgement	10,000	1,000 to 30,000
max_parallel	Publishes in flight	0 (no cap)	0 to 64
retry_*, late	As above

Errors: bad_topic (empty, + or #, or ~/ without a prefix), timeout, connect, auth, ssrf_blocked, node_not_ready, not_configured, circuit_open, limit. Only timeouts and connection failures retry.

Webhook

Sends the message to one of your organisation’s webhook endpoints: signed, retried and listed in the endpoint’s deliveries. This is the guaranteed-delivery path.

Setting	Meaning	Default	Values
endpoint	The endpoint	required	active endpoints subscribed to Automation message
topic	Sent as topic	{{ msg.topic }}	a template, 256 characters
body	What is sent besides the topic	payload	payload, payload and metadata
metadata_keys	Metadata keys sent	none	at most 20
late	See above	skip	skip, send

The receiver gets the event automation.message with topic, payload, originator, flowId, flowVersion, nodeId, actor and the listed metadata. out carries msg.metadata.webhook.deliveryId once queued. Errors: endpoint_not_found, endpoint_inactive, enqueue_failed, not_configured, node_not_ready, circuit_open, limit (webhooks not in your plan). See Webhooks.

Emit event

Sends an event that Event triggers with source flow hear, in any flow.

Setting	Meaning	Default	Values
kind	The event’s name	required	a lower-case letter first, then lower-case letters, digits, _ and .; up to 32 characters
data	What it carries	msg.payload	any value kind; a non-object is wrapped as { "value": … }

Listeners get msg.payload = the data and msg.topic flow/<kind>. Errors: rate_limited, invalid_value (a bad kind, or “emit: depth”: the fifth step of a chain). A deploy refuses a loop it can see (flow_cycle). A late message emits nothing.

Set variable

Stores a value in a flow or global variable.

Setting	Meaning	Values
path	The variable	flow.<name> or global.<name>, deeper keys allowed; flow.persist:<name> for the persistent store
value	What to store	any value kind; nothing (null) removes it

Errors: invalid_value, limit (store full; the old value stays). Limits: 1 MiB per flow, 4 MiB for global variables. In a test, the test’s own copy is written.

Timer

Starts, restarts or cancels a named timer. When it runs out, every Named timer trigger with that name fires.

Setting	Meaning	Default	Values
name	The timer, shared by all flows	required
op	Start (again) or cancel	start	start, cancel
ms	Duration (msg.ms overrides it)	1 min	0 to 7 days

Starting a running timer restarts it from zero: the watchdog pattern. Error queue_full “too many timers”: the organisation holds 64 timers of 60 s or less, or 10,000 longer ones. A late message starts or cancels nothing.

Enable or disable a flow

Switches another flow on or off, like the switch in the flow list.

Setting	Meaning	Default	Values
flow	The flow	required	a deployed flow of the organisation, not this one
state	Enable or disable	enable	enable, disable

out carries msg.metadata.flow_enable { flow, enabled, changed }. Errors: not_configured, self_reference, not_found, not_approved, conflict, invalid, limit (more than 6 switches a minute). Deploying a flow with this block needs the typed confirmation.

Run flow

Hands the message to another flow’s Flow input and ends this branch.

Setting	Meaning	Values
flow	The flow to run	another flow of the same host; never a root flow

No out port; nothing comes back. Errors: not_configured, invalid_value (missing, disabled or stopped), forbidden (a root), loop (fifth hop). A flow that other flows run cannot be deleted until those blocks are removed. The message keeps its device, so Save telemetry works in the target flow.

Link out

Passes the message to Link in blocks by name, or returns the answer to a Link call.

Setting	Meaning	Default	Values
mode	link (to Link in blocks) or return (answer the caller)	link	link, return
targets	Link in names (link mode)	empty	up to 16
name	The return’s name (return mode)	out	a return the caller declares

No out port. A missing target is a warning in the debug panel, not an error. A deploy refuses unknown names and loops with no waiting block (cycle_sync).

System log

Writes a line to the flow’s log (Activity > Events > Log, kept 24 hours).

Setting	Meaning	Default	Values
text	The line, with {{ }} placeholders	{{ msg.payload }}	up to 512 characters
level	Priority	info	info, notice, warn, err

Debug

Shows the messages that reach it in the editor’s Activity > Debug tab. No out port.

Setting	Meaning	Default	Values
property	What to show	msg.payload	msg (the whole message) or a path
active	Show messages at all	on	on, off

Debug entries are kept 24 hours and are visible to people who may debug. The button on the block switches it off and on without saving.

Write to an external time-series database

A block writes one point per message to an external time-series database server of your own, through a database server connection. Settings: the server, the bucket or database, the measurement, up to 16 tags, 1 to 32 fields (with a type: auto, float, int, string, bool), the time (default: the time of the first attempt, the same on every retry), timeout_ms (1,000 to 30,000), retries and late. out carries msg.metadata with the written measurement, fields and tags. For a general integration, the HTTP request block to your own API is often simpler.