step.when gates one workflow node

What workflow.steps.when is

step.when is a safe boolean guard evaluated after dependencies are complete and before one workflow node runs.

It is not Python eval. Hydra parses an allow-listed AST of comparisons, boolean operators, literals, lists, tuples, and parameter/environment placeholders.

What it contains

• Comparisons — Equality and ordered comparisons, with numeric coercion when appropriate.
• Boolean logic — and, or, and not.
• Safe values — Literals plus {{ param:NAME }} and {{ env:NAME }} placeholders.

Ready does not always mean run

Dependencies decide when a node is ready. when makes the final admission decision for that node without changing the topology of the graph.

Run the complete example

Copy this manifest from the verified documentation project, then run it from the repository root.

workflow:
  version: "1.0"
  name: docs_workflow
  description: Two actions used by the DSL documentation.
  trigger: {type: manual}
  steps:
    - name: prepare
      type: action
      action: log
      params: {message: "Preparation complete."}
      retry: {max: 2, delay: 0, backoff: fixed}
    - name: publish
      type: action
      action: log
      params: {message: "Publication complete."}
      depends_on: [prepare]
      when: "1 == 1"
      on_failure: fail

hdrctl workflow run examples/tutorial/dsl-elements/workflow.yaml

  ✓  Step 'prepare' OK (0.0s)
  ✓  Step 'publish' OK (0.0s)

  ✅ Workflow 'docs_workflow' completed in 0.0s — 2/2 steps OK

The relevant command syntax, copied from hdrctl workflow run --help:

hdrctl workflow run PATH
  PATH          path to workflow.yaml
  --lang LANG   interface language
  -h, --help    show command help

Close by

• workflow steps — graph nodes
• retry — attempts after admission
• parameters and environment
• workflow.yaml — full context
• Reference — when field