ServiceNow MCP Client not working

YashKumarV · yesterday

Hello Everyone.

I wanted to check if there is any update or official guidance on MCP Server compatibility with ServiceNow at the moment.

Issue I’m facing:

I have a custom MCP Server locally hosted
When I add it in ServiceNow AI Agent Studio and try to use it as a tool, I get the error:
“Unable to fetch tools for the MCP server”
The same MCP server works correctly when tested using:
- MCP Inspector
- Postman (as an MCP client)

Below are the record data from the MCP Execution Logs (sn_mcp_execution_logs) table:
Request = {"protocolVersion":"2025-06-18","clientInfo":{"version":"1.0.0","name":"Servicenow"},"capabilities":{}}

Error Message = Flow Action execution failed: Method failed: (/mcp/) with code: 406

Method = initialize

The error I got was related to the Content-Type headers where it shows that:

"error": {

"code": -32600,

"message": "Not Acceptable: Client must accept both application/json and text/event-stream"

}

Additional Errors Observed in ServiceNow System Logs:

Additional observation:

I was able to successfully add and use the open-source Microsoft Learning MCP Server in ServiceNow without any issues, which suggests the ServiceNow MCP client itself is functional.

So I wanted to understand:

Is ServiceNow MCP client currently limited to only application/json responses?
Is it possible to change the headers in ServiceNow to make it compatible with my custom MCP Server?
Are there any known limitations or required MCP server patterns (tool exposure, transport, headers, etc.) that custom servers must strictly follow?
Is there any update or planned fix to improve compatibility with custom/local MCP servers?

Any clarification or updates on this would be really helpful. Thanks!

@warren_chan

warren_chan · yesterday

I think depending on which version of the MCP Client you are running, it's possible that we are only supporting "application/json" as the content type. I do know that we have compatibility (not true support) for "text/event-streaming" in the later MCP Client versions. You should verify that you are running latest.

Everyone's local MCP server has been different so far, and frankly they have not been that easy to debug. I'll try to round a list of requirements from our side.

If it's your own MCP server, you can try relaxing the header requirements so that only "application/json" is required. If you're using FastMCP, I believe it's setting "json_response" to true.

YashKumarV · yesterday

Hi @warren_chan,

Thank you for the clarification.

Just to confirm, I am currently using the latest version of the MCP Client plugin (v1.1.2).

In our case, we do not own or control the MCP server, so unfortunately we are unable to relax or modify the header requirements on the server side.

Given this constraint, it would be really helpful if you could share the minimum required headers (and any other mandatory expectations) from the ServiceNow MCP client side, so we can validate whether the server aligns with them.

Looking forward to the list of requirements you mentioned. Thanks again for the support.

YashKumarV · yesterday

Hi @warren_chan ,

Thank you for the clarification.

Just to confirm, I am currently using the latest version of the MCP Client plugin (v1.1.2).
In our case, we do not own or control the MCP server, so unfortunately we are unable to relax or modify the header requirements on the server side.

Given this constraint, it would be really helpful if you could clarify the following from the ServiceNow MCP Client perspective:

Does the ServiceNow MCP Client currently support only application/json, only text/event-stream, or both content types?
You mentioned that text/event-stream has compatibility (not full support) in later MCP Client versions — could you please confirm which version introduced this compatibility? Since we are already on v1.1.2, we’d like to understand whether this version supports both headers or is limited to one.
Is there any way within ServiceNow to override or customize request headers for the MCP Client — for example via connection aliases, connections, flow actions, or any other configuration — so that we can test different header combinations?

Additionally, if you could share the minimum required headers and any other mandatory expectations from the ServiceNow MCP client side, that would help us validate whether the external MCP server aligns with them.

Thanks again for the guidance and support.

YashKumarV · yesterday

Hi @warren_chan ,

Thank you for the clarification.

Just to confirm, I am currently using the latest version of the MCP Client plugin (v1.1.2).
In our case, we do not own or control the MCP server, so unfortunately we are unable to relax or modify the header requirements on the server side.

Given this constraint, it would be really helpful if you could clarify the following from the ServiceNow MCP Client perspective:

Does the ServiceNow MCP Client currently support only application/json, only text/event-stream, or both content types headers?
You mentioned that text/event-stream has compatibility (not full support) in later MCP Client versions — could you please confirm which version introduced this compatibility? Since we are already on v1.1.2, we’d like to understand whether this version supports both headers or is limited to one.
Is there any way within ServiceNow to override or customize request headers for the MCP Client — for example via connection aliases, connections, flow actions, or any other configuration — so that we can test different header combinations?

Additionally, if you could share the minimum required headers and any other mandatory expectations from the ServiceNow MCP client side, that would help us validate whether the external MCP server aligns with them.

Thanks again for the guidance and support.