diff --git a/README.md b/README.md
index 85e95c60..648c4589 100644
--- a/README.md
+++ b/README.md
@@ -44,3 +44,22 @@ cargo test
 # Build .wasm packages
 cargo build --release --target wasm32-unknown-unknown
 ```
+
+### Refreshing `schema.graphql`
+
+After bumping `api_version` in the `shopify.extension.toml.liquid` files (or when a schema changes upstream), use `refresh-function-schemas.sh` to regenerate the committed `schema.graphql` for every function template. The script expands liquid templates locally, symlinks each flavor into a linked Shopify app's `extensions/` directory, and runs `shopify app function schema` against each template's own `api_version`. Nothing is cloned from GitHub — whatever is in your working tree is what gets refreshed.
+
+Prereqs: `bash`, `git`, `jq`, `yarn`, `@shopify/cli`, and a dev app you've already linked via `shopify app config link`.
+
+```shell
+# refresh every function's schema from the local working tree
+./refresh-function-schemas.sh --app-dir ~/path/to/linked-app
+
+# refresh only a subset
+./refresh-function-schemas.sh --app-dir ~/path/to/linked-app --only cart_transform,discount
+
+# leave the generated `schemagen-*` symlinks in the app for inspection
+./refresh-function-schemas.sh --app-dir ~/path/to/linked-app --keep
+```
+
+Run `./refresh-function-schemas.sh --help` for the full flag list. After it finishes, review with `git status` / `git diff` and commit any schema changes.
diff --git a/refresh-function-schemas.sh b/refresh-function-schemas.sh
new file mode 100755
index 00000000..449a951d
--- /dev/null
+++ b/refresh-function-schemas.sh
@@ -0,0 +1,123 @@
+#!/usr/bin/env bash
+#
+# refresh-function-schemas.sh — refresh schema.graphql for function templates.
+#
+# For every (function type, flavor) pair in templates.json, symlinks the
+# local template dir into a linked Shopify app's `extensions/` directory
+# and runs `shopify app function schema` to fetch the schema for the
+# api_version declared in that template's toml. Each flavor's schema is
+# fetched independently so the flavors can drift in api_version without
+# one overwriting another.
+#
+# Usage:
+#   ./refresh-function-schemas.sh --app-dir <path> [options]
+#
+# Required:
+#   --app-dir <path>     Linked Shopify app directory (must have shopify.app.toml)
+#
+# Options:
+#   --only <id[,id...]>  Refresh only these function identifiers.
+#                        Default: every function in templates.json.
+#   --keep               Leave generated extension symlinks in the app.
+#   -h, --help           Show this help.
+#
+# Operates on the extensions-templates checkout containing this script.
+#
+# Requirements: bash, git, jq, yarn, shopify CLI (@shopify/cli).
+#
+# Example:
+#   ./refresh-function-schemas.sh --app-dir ~/src/my-dev-app
+#   ./refresh-function-schemas.sh --app-dir ~/src/my-dev-app --only cart_transform,discount
+#
+set -euo pipefail
+
+TEMPLATES_REPO="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+APP_DIR=""
+ONLY=""
+KEEP=0
+
+usage() { sed -n '2,/^set -euo/p' "$0" | sed 's/^# \{0,1\}//; $d'; exit "${1:-0}"; }
+
+while [ $# -gt 0 ]; do
+  case "$1" in
+    --app-dir) APP_DIR="$2"; shift 2 ;;
+    --only)    ONLY="$2"; shift 2 ;;
+    --keep)    KEEP=1; shift ;;
+    -h|--help) usage 0 ;;
+    *) echo "Unknown arg: $1" >&2; usage 1 ;;
+  esac
+done
+
+[ -n "$APP_DIR" ] || { echo "--app-dir is required" >&2; usage 1; }
+[ -f "$APP_DIR/shopify.app.toml" ] || { echo "No shopify.app.toml in $APP_DIR — is it linked?" >&2; exit 1; }
+[ -f "$TEMPLATES_REPO/templates.json" ] || { echo "No templates.json in $TEMPLATES_REPO" >&2; exit 1; }
+command -v jq >/dev/null || { echo "jq is required" >&2; exit 1; }
+command -v yarn >/dev/null || { echo "yarn is required" >&2; exit 1; }
+command -v shopify >/dev/null || { echo "shopify CLI is required" >&2; exit 1; }
+
+only_match() {
+  [ -z "$ONLY" ] && return 0
+  case ",$ONLY," in *",$1,"*) return 0 ;; esac
+  return 1
+}
+
+echo "Expanding liquid templates..."
+for flavor in rust vanilla-js wasm; do
+  ( cd "$TEMPLATES_REPO" && yarn --silent expand-liquid "$flavor" >/dev/null )
+done
+
+ROWS=()
+while IFS= read -r line; do
+  ROWS+=("$line")
+done < <(
+  jq -r '
+    .[]
+    | select(.type == "function") as $t
+    | [$t.supportedFlavors[].path] | unique | .[] as $p
+    | [$t.identifier, $p] | @tsv
+  ' "$TEMPLATES_REPO/templates.json"
+)
+
+cleanup_list=()
+cleanup() {
+  [ "$KEEP" = 1 ] && return
+  for ext in "${cleanup_list[@]}"; do
+    rm -f "$APP_DIR/extensions/$ext"
+  done
+}
+trap cleanup EXIT
+
+mkdir -p "$APP_DIR/extensions"
+
+refreshed=0
+skipped=0
+for row in "${ROWS[@]}"; do
+  ID="$(printf '%s' "$row" | cut -f1)"
+  REL_PATH="$(printf '%s' "$row" | cut -f2)"
+  [ -n "$ID" ] && [ -n "$REL_PATH" ] || continue
+
+  if ! only_match "$ID"; then
+    skipped=$((skipped + 1)); continue
+  fi
+
+  TEMPLATE_DIR="$TEMPLATES_REPO/$REL_PATH"
+  if [ ! -f "$TEMPLATE_DIR/shopify.extension.toml" ]; then
+    echo "SKIP $REL_PATH (no expanded toml)"
+    skipped=$((skipped + 1)); continue
+  fi
+
+  EXT="schemagen-$REL_PATH"
+  LINK="$APP_DIR/extensions/$EXT"
+  rm -rf "$LINK"
+  ln -s "$TEMPLATE_DIR" "$LINK"
+  cleanup_list+=("$EXT")
+
+  echo ">> $REL_PATH — fetching schema"
+  ( cd "$APP_DIR" && shopify app function schema --path "$LINK" )
+
+  refreshed=$((refreshed + 1))
+done
+
+echo
+echo "Done. Refreshed: $refreshed, skipped: $skipped."
+echo "Review: (cd $TEMPLATES_REPO && git status)"