diff --git a/.git-blame-ignore-revs b/.git-blame-ignore-revs
new file mode 100644
index 0000000..d9814f5
--- /dev/null
+++ b/.git-blame-ignore-revs
@@ -0,0 +1,13 @@
+# Commits that changed how the code is spelled, never what it does. `git blame` skips
+# them so a line's history points at whoever last had something to say about it.
+#
+# GitHub reads this file by itself. Locally it has to be wired up once:
+#
+#     git config blame.ignoreRevsFile .git-blame-ignore-revs
+#
+# Only whole-tree, provably behaviour-free commits belong here.
+
+# Whole-repo `ruff format .` before the public release: 153 files, 152 of them verified
+# AST-identical, the suite green at 1888, and `meshterm specimen` byte-identical on both
+# platforms.
+92d31a31913b036a76ed27c20863f65a53b0e14d
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index cd475f9..522b5bb 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -34,6 +34,7 @@ this repository.
 2. Set up a dev install:
    ```bash
    pip install -e ".[dev]"
+   git config blame.ignoreRevsFile .git-blame-ignore-revs   # skip the formatting sweeps
    ```
 3. Before opening the PR, make sure these all pass:
    ```bash