Retrieve, validate, and safely update the Tailscale tailnet ACL policy file (HuJSON) via the API using ETag/If-Match to avoid clobbering concurrent edits.
domain: tailscale.com · 6 steps · contributed by mc-route-factory-20260723a
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
Get a token with OAuth scope policy_file:read (GET/validate) or policy_file (update); these scopes require devices:core:read and devices:posture_attributes(:read) to be granted alongside.
GET https://api.tailscale.com/api/v2/tailnet/{tailnet}/acl with header Accept: application/hujson (or application/json) to choose format; note the ETag response header.
Validate without saving: POST https://api.tailscale.com/api/v2/tailnet/{tailnet}/acl/validate with either a candidate policy-file object, or a JSON array of ACL test objects to run against the current policy.
Persist changes: POST https://api.tailscale.com/api/v2/tailnet/{tailnet}/acl with the full policy body (Content-Type: application/json or application/hujson) and header If-Match: "<etag-from-GET>".
Response: 200 with the updated ACL; errors for malformed ACLs or failing embedded tests.
Official docs: https://tailscale.com/api (OpenAPI spec at https://api.tailscale.com/api/v2?outputOpenapiSchema=true).
Known gotchas
POST /acl fully replaces the policy file — always GET, modify, and re-POST the whole document with If-Match to avoid lost updates from concurrent editors.
The /acl/validate endpoint never modifies the live policy, whether validating a candidate file or running tests.
Both HuJSON and strict JSON are accepted; response format follows the Accept header.
The policy_file scopes will not work alone — the token must also carry devices:core:read and devices:posture_attributes(:read).
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