The undeclared policy

Fifteen sections list the live resources sitting next to the declared ones: labels, autolinks, collaborators, actions_variables, agents_variables, rulesets, milestones, webhooks, custom_properties, deploy_keys, actions_secrets, dependabot_secrets, codespaces_secrets, agents_secrets, and secret_scanning_custom_patterns. Each has a default answer for a live resource the settings file does not declare, and each accepts a wrapped form that overrides it per file. This page is the normative statement of that policy: the knob, the defaults per section, and how it layers with a multi-repo defaults file. The README's Sections table states each section's default in its Undeclared default column; this page says what the defaults mean and how to change them.

The two forms

The plain array form is unchanged and keeps the section's default policy (in multi-repo mode a defaults file can set the policy instead - see layering below):

labels:
  - name: bug
    color: "d73a4a"

The wrapped form names the policy explicitly. entries holds exactly what the array form would, and a wrapper that omits undeclared behaves exactly like the plain array (the section default, or an inherited defaults-file policy, applies):

labels:
  undeclared: keep
  entries:
    - name: bug
      color: "d73a4a"

undeclared: delete removes live resources the file does not declare; undeclared: keep leaves them alone and surfaces each one as a note in the run log, so nothing disappears from view. In check mode, a resource a delete policy would remove is reported as drift; under keep it stays a note.

The wrapper takes only these two keys. Unlike entry fields, which pass through to GitHub, undeclared and entries are this action's own vocabulary, so a misspelled wrapper key fails validation before anything is written.

Defaults per section

Section	Default	The override buys you
labels	delete (Probot parity)	keep: manage a core set without deleting ad-hoc labels
autolinks	delete	keep: declare some references, tolerate the rest
collaborators	delete (owner always exempt)	keep: manage listed people without removing others
actions_variables	delete	keep: declare the managed variables, tolerate the rest
agents_variables	delete	keep: declare the managed variables, tolerate the rest
rulesets	keep	delete: make the file the complete ruleset inventory
milestones	keep	delete: prune stale milestones, with the caveat below
webhooks	keep (integrations create their own hooks)	delete: make the file the complete hook inventory
deploy_keys	keep (deployment tooling installs its own keys, and deleting a live key breaks whatever authenticates with it)	delete: make the file the complete key inventory
actions_secrets	keep	delete: prune stale secrets - a deleted secret's value is unrecoverable
dependabot_secrets	keep	delete: prune stale secrets - a deleted secret's value is unrecoverable
codespaces_secrets	keep	delete: prune stale secrets - a deleted secret's value is unrecoverable
agents_secrets	keep	delete: prune stale secrets - a deleted secret's value is unrecoverable
custom_properties	keep (an unset can revert to an org default the file does not model)	delete: make the file the complete property-value inventory, unsetting the rest
secret_scanning_custom_patterns	keep	delete: prune stale patterns - the pattern's alerts are resolved (never deleted), keeping the audit trail

The owner exemption for collaborators does not move with the knob: under undeclared: delete (the default) every undeclared direct collaborator is removed except the repository owner.

The nested variables, secrets, and deployment knobs

Four lists carry the same wrapped form WITHOUT being top-level sections: environments[].variables, environments[].secrets, environments[].deployment_branch_policies, and environments[].deployment_protection_rules. Each environment entry's list accepts the plain array or {undeclared, entries}, with its own fixed default: within a declared variables key the default is delete (the file is that environment's variable inventory), and the same holds for a declared deployment_branch_policies key (patterns are readable, recreatable configuration), while within a declared secrets key the default is keep, matching the top-level secret sections - a deleted secret's value is unrecoverable, so deletion stays opt-in. A declared deployment_protection_rules key also defaults to keep, for a security reason rather than an unrecoverable one: GitHub Apps can enable themselves as deployment gates, and silently disabling a gate the file never named would weaken a protection nobody asked to weaken - undeclared: delete opts into disabling. The knob is set per environment entry, and it never inherits a policy through the multi-repo defaults merge: arrays replace wholesale in that merge, so a target that declares environments replaces the defaults' entire environments array - individual entries never merge, and neither do the knobs inside them.

Deleting milestones detaches issues

Deleting a milestone does not delete the issues in it; it detaches the milestone from every issue that carried it, and there is no undo beyond re-assigning the issues by hand. That is why milestones keep undeclared entries by default. Set milestones: {undeclared: delete, ...} only when the settings file really is the complete list; the drift and change lines name the detachment every time, so a check run shows the consequence before an apply does it.

Layering with a multi-repo defaults file

In multi-repo mode the defaults file merges under every target the run processes (a repository with no settings file is skipped outright, defaults included), and the policy rides that merge as its own key:

• Entries never concatenate: a target that declares the section replaces the defaults' entry list wholesale, same as every other array.
• A target using the plain array form inherits the policy the defaults file set for that section.
• A target's explicit undeclared wins over the defaults'.

So a fleet can set the policy once. With this defaults file:

labels:
  undeclared: keep
  entries:
    - name: bug
      color: "d73a4a"

a target declaring labels: [{name: incident}] gets undeclared: keep with only its own entry, and a target declaring labels: {undeclared: delete, entries: [...]} keeps its own delete policy.

There is no way to set a policy without declaring an inventory: a defaults wrapper requires entries, and entries: [] is itself a declaration. A defaults-file section applies to every target the run processes, including targets whose settings file omits the section entirely - that is what a defaults file is. (A repository with no settings file at all is skipped outright, defaults included, and reported as skipped - the defaults never reach it.) So entries: [] under a policy declares an empty inventory fleet-wide. With undeclared: keep that only produces notes; with undeclared: delete it deletes every eligible resource on every processed target that does not declare the section itself. To harden a fleet's policy to delete, declare the fleet's entries in the same defaults section, so omitting targets keep them. A check run shows the resulting deletions as drift before an apply performs them.

One boundary to know about: HAVING a policy and INHERITING one are different things. The fifteen top-level section lists take the policy through the multi-repo defaults merge as described above. The nested environments[].variables, environments[].secrets, environments[].deployment_branch_policies, and environments[].deployment_protection_rules lists have their own knobs, set per environment entry with their own fixed defaults - they never inherit a policy from their section, from another list, or through the defaults merge.