diff --git a/categories/software-engineering/rules-to-better-net8-migrations.md b/categories/software-engineering/rules-to-better-net8-migrations.md
index 0e6503fe8f6..89e57a89b62 100644
--- a/categories/software-engineering/rules-to-better-net8-migrations.md
+++ b/categories/software-engineering/rules-to-better-net8-migrations.md
@@ -17,6 +17,7 @@ index:
 - know-how-to-migrate-web-config-to-asp-net-core
 - manage-compatibility-for-different-tfms
 - dotnet-upgrade-for-complex-projects
+- do-you-check-your-api-serialisation-format
 
 ---
 
diff --git a/rules/do-you-check-your-api-serialisation-format/rule.md b/rules/do-you-check-your-api-serialisation-format/rule.md
new file mode 100644
index 00000000000..880f7dd872b
--- /dev/null
+++ b/rules/do-you-check-your-api-serialisation-format/rule.md
@@ -0,0 +1,58 @@
+---
+type: rule
+title: Do you check your API serialisation format?
+uri: do-you-check-your-api-serialisation-format
+authors:
+  - title: Chris Clement
+    url: https://www.ssw.com.au/people/chris-clement/
+related:
+  - dotnet-upgrade-assistant
+  - migrate-from-system-web-to-modern-alternatives
+  - migration-plans
+  - modernize-your-app
+created: 2024-05-13T05:45:10.297Z
+guid: 5d3f3d8d-161f-4fdd-9721-e4e9f37de9ac
+---
+
+Most REST APIs serialise/deserialise to and from JSON format. To perform this serialisation, a .NET web application typically relies on either `Newtonsoft.Json` or `System.Text.Json`.
+
+Modern .NET applications prefer `System.Text.Json` over `Newtonsoft.Json` - which is commonly found in earlier versions of .NET and .NET Framework projects. 
+This, however, may break in certain usages.
+
+This issue needs to be addressed when migrating projects from .NET Framework to modern .NET.
+
+
+<!--endintro-->
+
+
+The primary reason for switching to `System.Text.Json` is its [faster performance and lower memory usage](https://devblogs.microsoft.com/dotnet/the-convenience-of-system-text-json/) compared to `Newtonsoft.Json`. However, it also breaks compatibility and lacks some features found in `Newtonsoft.Json`.
+
+
+## The differences
+[This Microsoft documentation](https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/migrate-from-newtonsoft?pivots=dotnet-9-0#table-of-differences) contains a compiled list of differences between `System.Text.Json` and `Newtonsoft.Json`.
+
+
+### Notable Things to Check
+
+- ⚠️ **Default Serialisation Property Name Casing**
+  
+  Since .NET Core 3.0, the default behaviour for JSON property name serialisation has switched to `camelCase`, whereas earlier versions followed the class's property names as-is (usually in `PascalCase`).
+  Couple of options to address this when migrating controllers from legacy endpoints while maintaining compatibility:
+    - **Option A:** Implement a per-controller override for migrated legacy APIs to maintain the same behaviour by setting `JsonSerializerOptions.PropertyNamingPolicy = null`, e.g., via a custom attribute using `ActionFilterAttribute`.
+    - **Option B:** Apply a global JSON serialisation override to retain `JsonSerializerOptions.PropertyNamingPolicy = null`.
+
+
+- ⚠️ **No Support for JSON Patch Documents**
+  
+  Deserialisation of JSON Patch documents might fail due to [lack of support for JSON Path queries](https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/migrate-from-newtonsoft?pivots=dotnet-9-0#json-path-queries-not-supported), e.g., commonly used in legacy `PATCH` endpoints.
+
+
+- ⚠️ **Limited OData Support**
+
+  OData might not work as expected when using `System.Text.Json`. See more: [Example issues](https://github.com/OData/AspNetCoreOData/issues/424).
+
+
+- ⚠️ **Limited Support for Date Formats**
+
+  While `System.Text.Json` [supports the ISO 8601-1:2019 format](https://learn.microsoft.com/en-us/dotnet/standard/datetime/system-text-json-support#the-extended-iso-8601-12019-profile-in-systemtextjson) for date and time components, `Newtonsoft.Json` accommodates a broader range of date-time strings. For example, `System.Text.Json` cannot deserialise the format `8:00am February, 24 2024`.
+
diff --git a/rules/dotnet-upgrade-for-complex-projects/rule.md b/rules/dotnet-upgrade-for-complex-projects/rule.md
index ef02e9770cc..1e8fbbc43eb 100644
--- a/rules/dotnet-upgrade-for-complex-projects/rule.md
+++ b/rules/dotnet-upgrade-for-complex-projects/rule.md
@@ -16,6 +16,7 @@ authors:
 related:
   - dotnet-upgrade-assistant
   - migrate-from-system-web-to-modern-alternatives
+  - do-you-check-your-api-serialisation-format
 created: 2023-07-16T23:08:53.979Z
 guid: 9de5ca88-a6aa-4fe5-af47-d6d2169cde86
 ---