Workflow Helper Functions
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This group is more situational, but it becomes valuable in complex flows where you need to inspect sibling results, build links back into Kestra, or summarize failures.

errorLogs()

Prints all error logs from the current execution:

{{ errorLogs() }}

It is most useful in errors blocks, where you need a compact summary of what failed without manually traversing task state objects.

currentEachOutput()

Use it inside ForEach flows to avoid manual taskrun.value indexing:

{{ currentEachOutput(outputs.make_data).values.data }}

tasksWithState()

Returns a list of task run objects matching the given state. Use it in error handlers or notifications to report which tasks failed:

{{ tasksWithState('FAILED') }}

Useful for building conditional logic or failure summaries based on task outcomes.

iterationOutput()

Retrieves the output of a specific iteration from a previous task. Both arguments are optional — taskId defaults to the current task and iteration defaults to the previous iteration:

{{ iterationOutput(outputs.myTask).value }}
{{ iterationOutput(outputs.myTask, 2).value }}

parentOutput()

Retrieves the output of a parent task. The optional index argument specifies which ancestor to target; omitting it returns the direct parent’s output:

{{ parentOutput() }}
{{ parentOutput(1) }}

subflow()

Synchronously runs a subflow and returns its terminal execution result, so you can read the subflow’s outputs, state, or labels from within an expression.

{{ subflow(namespace='company.team', id='my_subflow', inputs={'key': 'value'}).outputs.my_output }}

Arguments:

ArgumentRequiredDescription
namespaceYesNamespace of the subflow to run
idYesFlow ID of the subflow to run
inputsNoMap of inputs to pass to the subflow
revisionNoSpecific revision to run; defaults to latest
labelsNoLabels to attach to the subflow execution
timeoutNoISO 8601 duration; defaults to PT1M, hard cap PT5M

Return value — an object with four fields:

FieldTypeDescription
.idstringExecution ID of the subflow run
.statestringTerminal state name, e.g. SUCCESS, FAILED
.outputs.<key>anyFlow-level outputs declared in the subflow’s outputs: block
.labels.<key>stringExecution labels as a key → value map

Primary use case — populating a SELECT or MULTISELECT input’s expression: at form render time:

inputs:
  - id: datacenter
    type: SELECT
    expression: "{{ subflow(namespace='company.ops', id='fetch_datacenters').outputs.datacenter_list }}"

When a user opens the Execute form, Kestra runs the subflow synchronously, reads its output, and populates the dropdown before the main flow begins.

Important constraints:

  • Only valid in an input expression: context. Using subflow() inside a task or trigger property throws an error, because blocking a worker thread while waiting for a child execution can deadlock a worker under load.
  • Only available on WEBSERVER and STANDALONE server types. The function is not registered on other server types.
  • The default timeout is PT1M. The hard cap is PT5M — passing a larger timeout value is rejected at runtime. Both limits are configurable; see configuration reference.
  • Subflow recursion depth is capped at 3. A subflow whose own inputs call subflow() counts against this limit.
  • Executions triggered by subflow() carry a system.from: subflow label automatically.

Enterprise Edition’s appLink() builds links back to Kestra Apps:

{{ appLink(appId='com.example.my-app') }}
{{ appLink(baseUrl=true) }}

Use it in notifications when you want recipients to jump directly into the related app rather than the generic flow UI.

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