Table of Contents

Class McpHeaderAttribute

Namespace
ModelContextProtocol.Server
Assembly
ModelContextProtocol.Core.dll

Indicates that a tool parameter should be mirrored as an HTTP header in client requests.

[AttributeUsage(AttributeTargets.Property|AttributeTargets.Parameter)]
public sealed class McpHeaderAttribute : Attribute
Inheritance
McpHeaderAttribute
Inherited Members

Examples

[McpServerTool]
public static string ExecuteSql(
    [McpHeader("Region")] string region,
    string query)
{
    // The client will add header: Mcp-Param-Region: {region value}
}

Remarks

When applied to a parameter, the SDK will include an x-mcp-header extension property in the parameter's JSON schema. Clients will then mirror this parameter's value into an HTTP header named Mcp-Param-{Name}.

Only parameters with primitive types (integer, string, boolean) may use this attribute. The header name must match HTTP field-name token syntax (tchar per RFC 9110 Section 5.6.2) and must be case-insensitively unique within the tool's input schema.

This enables network infrastructure such as load balancers, proxies, and gateways to make routing decisions based on tool parameter values without parsing the JSON-RPC request body.

Constructors

McpHeaderAttribute(string)

Initializes a new instance of the McpHeaderAttribute class.

public McpHeaderAttribute(string name)

Parameters

name string

The name portion of the header. The full header name will be Mcp-Param-{name}. Must match HTTP field-name token syntax (tchar per RFC 9110 Section 5.6.2).

Exceptions

ArgumentException

The name is null, empty, or contains invalid characters.

Properties

Name

Gets the name portion of the header.

public string Name { get; }

Property Value

string

Remarks

The full header name sent by clients will be Mcp-Param-{Name}.

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