diff --git a/.prettierignore b/.prettierignore
new file mode 100644
index 0000000..0f2c12a
--- /dev/null
+++ b/.prettierignore
@@ -0,0 +1,9 @@
+# settings.json and settings2.json are hand-compacted on purpose: the permission
+# allow-lists are grouped by stack on single lines so they read as a table. Prettier's
+# defaults would expand each into ~60 lines, turning any one-line edit into an
+# unreviewable diff. Prettier is not part of the quality gate (§19.3), so it has no
+# business rewriting them. The hooks/format.sh PostToolUse hook honors this file, so
+# editing either settings file no longer triggers a reformat. Everything else
+# (Markdown, and real code in repos that use this config) is still formatted normally.
+settings.json
+settings2.json
diff --git a/STRUCTURE.md b/STRUCTURE.md
index b25c5b1..a039442 100644
--- a/STRUCTURE.md
+++ b/STRUCTURE.md
@@ -31,6 +31,7 @@ Per-repo CLAUDE.md (§19 only; inherits spine + whichever rule pack your files p
 Repo-only, not installed:
    tests/hooks/               # behavioral tests for all three hooks (stdin JSON → exit code); run by the §19.3 gate
    .github/workflows/gate.yml # CI: the §19.3 gate on every PR and on push to main
+   .prettierignore            # keeps format.sh's prettier off the hand-compacted settings*.json
 ```
 
 ## Install (Mac)