diff --git a/.github/instructions/cdac.instructions.md b/.github/instructions/cdac.instructions.md
index 8715be06e224c8..5339f3543e7864 100644
--- a/.github/instructions/cdac.instructions.md
+++ b/.github/instructions/cdac.instructions.md
@@ -1,5 +1,5 @@
 ---
-applyTo: "src/native/managed/cdac/**"
+applyTo: "src/native/managed/cdac/**,docs/design/datacontracts/**,src/coreclr/**/datadescriptor/**"
 ---
 
 # cDAC — Folder-Specific Guidance
@@ -32,3 +32,16 @@ When porting `HRESULT`-returning APIs to throw exceptions, the following mapping
 - `ArgumentException` → for `E_INVALIDARG`
 - `NullReferenceException` → for `E_POINTER`
 - `InvalidCastException` → for `E_NOINTERFACE`
+
+## Documentation updates (ALL branches)
+
+`docs/design/datacontracts/<Name>.md` is the authoritative spec of each contract (1:1 with `Abstractions/Contracts/I<Name>.cs`). If the PR changes any of the following without also updating the doc, **MUST** flag it as an error citing the exact doc file:
+
+- **`Abstractions/Contracts/I<Name>.cs`** — added, removed, or renamed methods, or new exposed types/enums.
+- **`Contracts/Contracts/<Name>_<N>.cs`** — a new version file (needs a new `## Version N` section), or a semantic change to an existing version's algorithm. Pure refactors don't need doc updates.
+- **New contract** (new `I<Name>.cs` + `<Name>_1.cs`) — needs a new `docs/design/datacontracts/<Name>.md`.
+- **`src/coreclr/**/datadescriptor/**`** — added, removed, or renamed types, fields, or globals may need a matching update in every consuming contract's doc; check whichever contracts' algorithms are affected.
+
+Do **NOT** require doc updates for pure refactors, test-only changes, bug fixes that restore documented behavior, `Legacy/**` (SOSDacImpl, DacDbi shim), or build/CI changes.
+
+