XML Validation in APIM policy not working correctly

Question

XML Validation in APIM policy not working correctly

Johnson, Dana 0

Gents, I'm trying to validate an XML document against an XSD schema using the following:

<validate-content

unspecified-content-type-action="prevent"

max-size="1048576"

size-exceeded-action="prevent"

errors-variable-name="validationErrors">

<content

    type="application/xml"

    validate-as="xml"

     schema-id="MySchema"

    action="prevent" />
</validate-content>

The Validate Content does not work no matter what I add or change in the properties

Any suggestions would be greatly appreciated

Rakesh Mishra 11,095 Reputation points Microsoft External Staff Moderator

2026-07-31T14:25:49.6266667+00:00
Hello @Johnson, Dana ,

Welcome to the Microsoft Q&A Platform! Thank you for asking your question here.

Troubleshooting the validate-content policy for XML payloads can be tricky because XML validation in Azure API Management strictly depends on both the APIM configuration and the exact structural nuances of your payload.

Based on your policy snippet, here are the most common reasons why it might not be working and the steps to fix it:

1. Extract the Exact Error via API Tracing

Since you defined errors-variable-name="validationErrors", APIM is already capturing the exact reason for the failure. The fastest way to solve this is to look at the trace:

Temporarily change the policy actions from "prevent" to "detect" (i.e., action="detect" and unspecified-content-type-action="detect").

Go to the Test tab in the Azure Portal, enable Trace, and fire a test request with your XML payload.

Review the Trace output. Look for the validationErrors context variable. It will give you the exact line number, position, and reason for the XSD failure (e.g., "API's schema does not exist" or "Body of the request does not conform...").

2. Verify the Content-Type Header

Your policy explicitly targets <content type="application/xml">.

If your client tool (like Postman or curl) defaults to sending text/xml or leaves the header out entirely, the request will immediately hit your unspecified-content-type-action="prevent" condition and fail with a 400 Bad Request before the schema is even checked.

Fix: Ensure the incoming request explicitly includes the Content-Type: application/xml header.

3. XML Namespace Mismatches (Most Common Culprit)

XSD validation in APIM strictly enforces XML namespaces.

Open your schema definition in APIM and locate the targetNamespace attribute.

Look at the root element of your incoming XML payload and locate the xmlns attribute.

Fix: These two must match perfectly. If your schema expects a namespace but your XML payload omits it (or vice-versa), the validation will fail because the processor won't recognize the elements.

4. Schema Location and Naming

The schema-id="MySchema" attribute relies on the schema being properly registered in the APIM instance.

Navigate to your APIM instance in the Azure Portal, go to APIs > Schemas (or the specific API's schema section).

Ensure that the schema is uploaded, the name exactly matches MySchema (it is case-sensitive), and the schema type is set to XML.

5. Policy Scope

Double-check that your <validate-content> snippet is placed inside the <inbound> block of your policy so it catches the incoming request before it reaches the backend.

Let me know if checking the APIM Trace reveals a specific error message, and we can look into it further.

XML Validation in APIM policy not working correctly

Your answer