diff --git a/.claude/rules/code-comments.md b/.claude/rules/code-comments.md
index 05f2d28e4..02f179fab 100644
--- a/.claude/rules/code-comments.md
+++ b/.claude/rules/code-comments.md
@@ -1,11 +1,12 @@
 ## JS/Go Code Comment Rules
 
-Doc comments for packages and exported identifiers must be complete sentences that begin with the name of the thing being described and end with a period.
-
 A doc comment is **required** for every function (including unexported helpers), as well as for every non-trivial Vue `methods:` / `computed:` / watcher:
 - Keep comments **compact** and default to one line for WHAT in the format `// Name does X.`. Skip trivial getters (`isOpen: () => this.open`).
 - Add up to three follow-up lines (`// …`) only when the WHY is non-obvious: a hidden invariant, a workaround that would otherwise be undone by a future cleanup, a contract a reader can't infer from the code.
 - If readers can derive the WHY from the function body or a nearby line, leave it out. Multi-paragraph explanations belong in `specs/`, package `README.md` files, or GitHub issues — never in the source itself.
 - For short examples in comments, indent code instead of using backticks.
 
+Doc comments for packages and exported identifiers must be complete sentences that begin with the name of the thing being described and end with a period.
+Use US English spelling in all code comments (`parameterized`, `behavior`, `color`, `serialize`, `normalize`, `optimize`, …) — not the British `-ised`/`-our`/`-re` variants. Identifiers in code that already use a different spelling (e.g. an existing exported symbol) are not in scope; only the prose in comments and doc strings.
+
 > **Don't include in code comments:** Issue / PR numbers, "previously…" history, alternatives considered, what the function used to do, references to old commits, names of subsequent reviewers, or any narrative that names the change rather than the steady-state behavior. That context belongs in commit messages, specs, or handover notes.
diff --git a/AGENTS.md b/AGENTS.md
index bbe1fa274..9968a63db 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -107,14 +107,15 @@ Title Case rules (Chicago-style, with code- and path-aware normalization):
 
 ### JS/Go Code Comments
 
-Doc comments for packages and exported identifiers must be complete sentences that begin with the name of the thing being described and end with a period.
-
 A doc comment is **required** for every function (including unexported helpers), as well as for every non-trivial Vue `methods:` / `computed:` / watcher:
 - Keep comments **compact** and default to one line for WHAT in the format `// Name does X.`. Skip trivial getters (`isOpen: () => this.open`).
 - Add up to three follow-up lines (`// …`) only when the WHY is non-obvious: a hidden invariant, a workaround that would otherwise be undone by a future cleanup, a contract a reader can't infer from the code.
 - If readers can derive the WHY from the function body or a nearby line, leave it out. Multi-paragraph explanations belong in `specs/`, package `README.md` files, or GitHub issues — never in the source itself.
 - For short examples in comments, indent code instead of using backticks.
 
+Doc comments for packages and exported identifiers must be complete sentences that begin with the name of the thing being described and end with a period.
+Use US English spelling in all code comments (`parameterized`, `behavior`, `color`, `serialize`, `normalize`, `optimize`, …) — not the British `-ised`/`-our`/`-re` variants. Identifiers in code that already use a different spelling (e.g. an existing exported symbol) are not in scope; only the prose in comments and doc strings.
+ 
 > **Don't include in code comments:** Issue / PR numbers, "previously…" history, alternatives considered, what the function used to do, references to old commits, names of subsequent reviewers, or any narrative that names the change rather than the steady-state behavior. That context belongs in commit messages, specs, or handover notes.
 
 ## Agent Runtime