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Variables do three jobs at once. They are the environment variables the steps read, the form fields the UI renders, and the entries in the generated manifest that tells someone what to supply.
Names are uppercase environment-variable style — [A-Z][A-Z0-9_]*. The KEEL_ prefix is reserved for the metadata Keel injects into every run.

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Required, optional, and defaults

Variables are required unless required: false. A default satisfies a required variable without any input, and pre-fills the form. The form makes the distinction visible at a glance:
  • A red asterisk marks fields that need input — required, with no default.
  • optional marks fields with required: false.
  • Fields with a default show neither; the default applies when left blank.
Each collapsible group in a large form also shows how many of its fields still need input, so you never have to open every group to find out. How a value reaches the run follows from this: a variable resolves to its saved value, else its default. An optional variable with neither is not exported at all — read it as ${NAME:-} in steps. Booleans are the exception: an unset boolean resolves to false.

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Types

The type decides the form control and the validation: Details for each are in the variable types reference.

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Validation

validation adds constraints beyond the type: a regular expression the whole value must match (with a custom message), numeric bounds, and length bounds. The form shows the constraints under the field before you type, so nobody has to guess the format, and the same rules run again on save and on deploy. See the validation reference.

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Secrets

secret: true marks a value as sensitive. Secrets are encrypted at rest (AES-256-GCM), rendered as password fields that never echo the saved value, masked as ••• wherever they appear in run logs, and never printed by keel deploy. A saved secret can be left blank on the form to keep it, or overwritten with a new value. Secrets cannot have defaults, and boolean and select variables cannot be secret. The secrets guide follows a value from form to log.

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Deploy-time variables

Most variables are configuration — set once per target and reused. A variable with deploy_time: true is asked for every time a deploy starts, in a modal, and applies to that run only. Use it for choices that change per run: an image tag, a plan-versus-apply switch, a destroy confirmation. See Deploy-time and conditional variables.

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Conditional variables

when: gates a variable on another variable’s value. While the condition does not hold, the variable is inactive: disabled in the form (re-enabled live as values change), never required, and not exported into the run. Conditions chain and are validated for cycles and impossible comparisons. See the conditions reference.

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Layout

With many variables, groups, row, and flex organize the form into collapsible sections and side-by-side fields. Without them, the form is one variable per line in document order. See Organize large forms.

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Documentation

label, description (Markdown), placeholder, and the manifest block’s why and how are what the person filling in the form — or reading the generated manifest — actually sees. Write them for that person. See Variable manifests.