diff --git a/.github/workflows/update_metadata.yml b/.github/workflows/update_metadata.yml
new file mode 100644
index 000000000..82a36230f
--- /dev/null
+++ b/.github/workflows/update_metadata.yml
@@ -0,0 +1,40 @@
+# This workflow updates the check_metadata.sh script, which compares the current
+# size of build artifacts against their size in the previous version of Blockly.
+
+name: Update Metadata
+
+on: [workflow_dispatch]
+
+jobs:
+  update-metadata:
+    runs-on: ubuntu-latest        
+
+    steps:
+    - name: Check Out Blockly
+      uses: actions/checkout@v2
+      with:
+        ref: 'develop'
+
+    - name: Use Node.js 16.x
+      uses: actions/setup-node@v1
+      with:
+        node-version: 16.x
+
+    - name: Build Blockly
+      run: npm run build:compressed
+
+    - name: Build Blockly blocks
+      run: npm run build:blocks
+
+    - name: Update Metadata
+      run: source ./tests/scripts/update_metadata.sh
+
+    - name: Create Pull Request
+      uses: peter-evans/create-pull-request@9825ae65b1cb54b543b938503728b432a0176d29
+      with:
+        commit-message: Update build artifact sizes in check_metadata.sh
+        delete-branch: true
+        title: Update build artifact sizes in check_metadata.sh
+
+    - name: View Pull Request
+      run: echo "View Pull Request - ${{ steps.cpr.outputs.pull-request-url }}"
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diff --git a/tests/scripts/update_metadata.sh b/tests/scripts/update_metadata.sh
new file mode 100755
index 000000000..d3b97f3ab
--- /dev/null
+++ b/tests/scripts/update_metadata.sh
@@ -0,0 +1,34 @@
+#!/bin/bash
+
+# Determines the size of generated files and updates check_metadata.sh to
+# reflect the new values.
+
+gzip -k build/blockly_compressed.js
+gzip -k build/blocks_compressed.js
+
+blockly_size=$(wc -c < "build/blockly_compressed.js")
+blocks_size=$(wc -c < "build/blocks_compressed.js")
+blockly_gz_size=$(wc -c < "build/blockly_compressed.js.gz")
+blocks_gz_size=$(wc -c < "build/blocks_compressed.js.gz")
+quarter=$(date "+Q%q %Y")
+version=$(npx -c 'echo "$npm_package_version"')
+
+replacement="# ${quarter}\t${version}\t${blockly_size}\n"
+replacement+="readonly BLOCKLY_SIZE_EXPECTED=${blockly_size}"
+sed -ri "s/readonly BLOCKLY_SIZE_EXPECTED=[0-9]+/${replacement}/g" \
+  tests/scripts/check_metadata.sh
+
+replacement="# ${quarter}\t${version}\t${blocks_size}\n"
+replacement+="readonly BLOCKS_SIZE_EXPECTED=${blocks_size}"
+sed -ri "s/readonly BLOCKS_SIZE_EXPECTED=[0-9]+/${replacement}/g" \
+  tests/scripts/check_metadata.sh
+
+replacement="# ${quarter}\t${version}\t${blockly_gz_size}\n"
+replacement+="readonly BLOCKLY_GZ_SIZE_EXPECTED=${blockly_gz_size}"
+sed -ri "s/readonly BLOCKLY_GZ_SIZE_EXPECTED=[0-9]+/${replacement}/g" \
+  tests/scripts/check_metadata.sh
+
+replacement="# ${quarter}\t${version}\t${blocks_gz_size}\n"
+replacement+="readonly BLOCKS_GZ_SIZE_EXPECTED=${blocks_gz_size}"
+sed -ri "s/readonly BLOCKS_GZ_SIZE_EXPECTED=[0-9]+/${replacement}/g" \
+  tests/scripts/check_metadata.sh
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