diff --git a/.github/workflows/mddiffcheck.yml b/.github/workflows/mddiffcheck.yml
new file mode 100644
index 000000000..4cb8d0865
--- /dev/null
+++ b/.github/workflows/mddiffcheck.yml
@@ -0,0 +1,19 @@
+name: 'Check CAP Diffs'
+
+on:
+  push:
+    branches:
+    - master
+  pull_request:
+
+jobs:
+  mddiffcheck:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Go
+      uses: actions/setup-go@v2
+      with:
+        go-version: ^1.16
+    - run: go get github.com/stellar/mddiffcheck
+    - run: mddiffcheck -repo https://github.com/stellar/stellar-core core/*.md
diff --git a/core/cap-0021.md b/core/cap-0021.md
index 6ea6e24de..b1c9001b1 100644
--- a/core/cap-0021.md
+++ b/core/cap-0021.md
@@ -287,7 +287,7 @@ the same block.
 
 ### XDR diff
 
-```diff
+```diff mddiffcheck.base=v16.0.0
 diff --git a/src/xdr/Stellar-ledger-entries.x b/src/xdr/Stellar-ledger-entries.x
 index 26ff33d43..d96f55ea6 100644
 --- a/src/xdr/Stellar-ledger-entries.x
diff --git a/core/cap-0035.md b/core/cap-0035.md
index a9b17dcc8..d686dff1b 100644
--- a/core/cap-0035.md
+++ b/core/cap-0035.md
@@ -97,7 +97,7 @@ flags. This operation can be used to unset `TRUSTLINE_CLAWBACK_ENABLED_FLAG`.
 
 This patch of XDR changes is based on the XDR files in tag/commit `v15.1.0` (`90b2780584c6390207bf09291212d606896ce9f8`) of [stellar-core].
 
-```diff
+```diff mddiffcheck.base=v15.1.0
 diff --git a/src/xdr/Stellar-ledger-entries.x b/src/xdr/Stellar-ledger-entries.x
 index 8d7463915..26ff33d43 100644
 --- a/src/xdr/Stellar-ledger-entries.x
diff --git a/core/cap-0036.md b/core/cap-0036.md
index e66ef6881..1d68d6e1d 100644
--- a/core/cap-0036.md
+++ b/core/cap-0036.md
@@ -69,7 +69,7 @@ destroyed as if it had been claimed by a claimaint.
 
 This patch of XDR changes is based on the XDR files as they are after the XDR changes from CAP-35 are applied.
 
-```diff
+```diff mddiffcheck.ignore=true
 --- a/src/xdr/Stellar-transaction.x
 +++ b/src/xdr/Stellar-transaction.x
 @@ -47,7 +47,8 @@ enum OperationType
diff --git a/core/cap-0037.md b/core/cap-0037.md
index 591d82fc7..a60a2467e 100644
--- a/core/cap-0037.md
+++ b/core/cap-0037.md
@@ -85,7 +85,7 @@ their funds to the pool, participating in the collective liquidity allocation.
 
 ### XDR changes
 
-```diff
+```diff mddiffcheck.ignore=true
 --- a/src/xdr/Stellar-ledger-entries.x
 +++ b/src/xdr/Stellar-ledger-entries.x
 @@ -403,6 +403,43 @@ struct ClaimableBalanceEntry
@@ -165,7 +165,7 @@ their funds to the pool, participating in the collective liquidity allocation.
  };
 ```
 
-```diff
+```diff mddiffcheck.ignore=true
 --- a/src/xdr/Stellar-transaction.x
 +++ b/src/xdr/Stellar-transaction.x
 @@ -48,7 +48,9 @@ enum OperationType
@@ -647,4 +647,4 @@ every `LiquidityPoolEntry` requires at least one `LiquidityStakeEntry`.
 
 ## Security Concerns
 
-TBD
\ No newline at end of file
+TBD
diff --git a/core/cap-0038.md b/core/cap-0038.md
index 08b7cf83c..12513a815 100644
--- a/core/cap-0038.md
+++ b/core/cap-0038.md
@@ -57,7 +57,7 @@ exchanging assets with the order book and liquidity pools.
 
 ### XDR changes
 This patch of XDR changes is based on the XDR files in commit (`afb2dca9e112c79547e5125c1e45a8e94c9b965b`) of stellar-core.
-```diff
+```diff mddiffcheck.base=afb2dca9e112c79547e5125c1e45a8e94c9b965b
 diff --git a/src/xdr/Stellar-ledger-entries.x b/src/xdr/Stellar-ledger-entries.x
 index 0e7bc842..73a17001 100644
 --- a/src/xdr/Stellar-ledger-entries.x
diff --git a/core/cap-0039.md b/core/cap-0039.md
index 991037dc2..5e700d5a1 100644
--- a/core/cap-0039.md
+++ b/core/cap-0039.md
@@ -61,7 +61,7 @@ accounts for contracts, such as payment channels.
 This patch of XDR changes is based on the XDR files in commit
 `b9e10051eafa1125e8d238a47e5915dad30c2640` of stellar-core.
 
-```diff
+```diff mddiffcheck.base=b9e10051eafa1125e8d238a47e5915dad30c2640
 diff --git a/src/xdr/Stellar-ledger-entries.x b/src/xdr/Stellar-ledger-entries.x
 index 0e7bc842..68c52758 100644
 --- a/src/xdr/Stellar-ledger-entries.x