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feat: add support for custom HTTP headers in StreamableHttpClient - #655

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Feb 13, 2026
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feat: add support for custom HTTP headers in StreamableHttpClient#655
alexhancock merged 2 commits into
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arichyx:feat/reqwest-support-custom-headers

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@arichyxarichyx commented Feb 13, 2026

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This PR adds support for custom HTTP headers in the StreamableHttpClient transport, allowing users to pass additional headers when connecting to remote MCP servers.

Motivation and Context

When connecting to the GitHub MCP server remotely, custom headers are required to filter and control server behavior. Specifically, the GitHub MCP server uses the X-MCP-Toolsets header to allow clients to specify which toolsets to load (e.g., X-MCP-Toolsets: issues to only load issue-related tools).

Reference: https://github.com/github/github-mcp-server/blob/main/docs/remote-server.md

The Rust SDK did not previously support custom headers, making it impossible to use these filtering capabilities. This PR addresses that limitation by adding custom header support to the StreamableHttpClient transport configuration.

How Has This Been Tested?

  • Unit tests: Added tests for configuration API, including default behavior, single/multiple headers, and interaction with existing auth_header
  • Integration test: Added end-to-end test that spins up a test HTTP server and verifies custom headers are correctly sent in MCP protocol requests
  • Test scenarios:
    • Default empty headers (backward compatibility)
    • Single custom header
    • Multiple custom headers
    • Custom headers combined with auth_header
    • Headers sent during initialize, initialized notification, and regular requests

All tests pass locally with just test.

Breaking Changes

None. This is a fully backward-compatible addition. Existing code continues to work without modification, as custom headers default to an empty HashMap.

Types of changes

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Breaking change (fix or feature that would cause existing functionality to change)
  • Documentation update

Checklist

  • I have read the MCP Documentation
  • My code follows the repository's style guidelines
  • New and existing tests pass locally
  • I have added appropriate error handling
  • I have added or updated documentation as needed

Additional context

Implementation details:

  • Added custom_headers: HashMap<HeaderName, HeaderValue> field to StreamableHttpClientTransportConfig
  • Added custom_headers() builder method for fluent API configuration
  • Updated StreamableHttpClient trait's post_message method signature to accept custom headers
  • Modified reqwest implementation to apply custom headers to all HTTP requests
  • Updated auth client wrapper to forward custom headers

Example usage:

use std::collections::HashMap;use http::{HeaderName,HeaderValue};use rmcp::transport::streamable_http_client::StreamableHttpClientTransportConfig;// Configure custom headers for GitHub MCP serverletmut headers = HashMap::new();
headers.insert(HeaderName::from_static("x-mcp-toolsets"),HeaderValue::from_static("issues"));let config = StreamableHttpClientTransportConfig::with_uri("https://mcp.github.com").custom_headers(headers);

@github-actionsgithub-actionsBot added T-dependencies Dependencies related changes T-test Testing related changes T-config Configuration file changes T-core Core library changes T-transport Transport layer changes labels Feb 13, 2026
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alexhancock self-requested a review February 13, 2026 15:28
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This is a good idea - thanks for the contribution. I left one recommendation in the code.

Comment threadcrates/rmcp/src/transport/common/reqwest/streamable_http_client.rs
request = request.bearer_auth(auth_header);
}
// Apply custom headers
for (name, value) in custom_headers {

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Perhaps disallow any of the headers that are controlled by the default client logic?

ACCEPTHEADER_SESSION_ID etc

@alexhancockalexhancockFeb 13, 2026

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I would check https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#streamable-http for a full list

MCP-Protocol-Version is another one that comes to mind

@arichyxarichyxFeb 13, 2026

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Good idea. I've updated the PR to add the check.

@alexhancock
alexhancock merged commit 016b7d3 into modelcontextprotocol:mainFeb 13, 2026
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Nice one @Arichy - thanks

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feat: add support for custom HTTP headers in StreamableHttpClient by arichyx · Pull Request #655 · modelcontextprotocol/rust-sdk · GitHub
Skip to content
feat: add support for custom HTTP headers in StreamableHttpClient - #655
Merged
alexhancock merged 2 commits into
modelcontextprotocol:mainfrom 
arichyx:feat/reqwest-support-custom-headers
Feb 13, 2026
Merged
feat: add support for custom HTTP headers in StreamableHttpClient#655
alexhancock merged 2 commits into
modelcontextprotocol:mainfrom 
arichyx:feat/reqwest-support-custom-headers
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@arichyx
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Feb 13, 2026

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This PR adds support for custom HTTP headers in the StreamableHttpClient transport, allowing users to pass additional headers when connecting to remote MCP servers.
Motivation and Context
When connecting to the GitHub MCP server remotely, custom headers are required to filter and control server behavior. Specifically, the GitHub MCP server uses the X-MCP-Toolsets header to allow clients to specify which toolsets to load (e.g., X-MCP-Toolsets: issues to only load issue-related tools).
Reference: https://github.com/github/github-mcp-server/blob/main/docs/remote-server.md
The Rust SDK did not previously support custom headers, making it impossible to use these filtering capabilities. This PR addresses that limitation by adding custom header support to the StreamableHttpClient transport configuration.
How Has This Been Tested?
  • Unit tests: Added tests for configuration API, including default behavior, single/multiple headers, and interaction with existing auth_header
  • Integration test: Added end-to-end test that spins up a test HTTP server and verifies custom headers are correctly sent in MCP protocol requests
  • Test scenarios:

    • Default empty headers (backward compatibility)
    • Single custom header
    • Multiple custom headers
    • Custom headers combined with auth_header
    • Headers sent during initialize, initialized notification, and regular requests
All tests pass locally with just test.
Breaking Changes
None. This is a fully backward-compatible addition. Existing code continues to work without modification, as custom headers default to an empty HashMap.
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
  •  New feature (non-breaking change which adds functionality)
  •  Breaking change (fix or feature that would cause existing functionality to change)
  •  Documentation update
Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
Implementation details:
  • Added custom_headers: HashMap<HeaderName, HeaderValue> field to StreamableHttpClientTransportConfig
  • Added custom_headers() builder method for fluent API configuration
  • Updated StreamableHttpClient trait's post_message method signature to accept custom headers
  • Modified reqwest implementation to apply custom headers to all HTTP requests
  • Updated auth client wrapper to forward custom headers
Example usage:
use std::collections::HashMap;use http::{HeaderName,HeaderValue};use rmcp::transport::streamable_http_client::StreamableHttpClientTransportConfig;// Configure custom headers for GitHub MCP serverletmut headers = HashMap::new();
headers.insert(HeaderName::from_static("x-mcp-toolsets"),HeaderValue::from_static("issues"));let config = StreamableHttpClientTransportConfig::with_uri("https://mcp.github.com").custom_headers(headers);
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This is a good idea - thanks for the contribution. I left one recommendation in the code.
Comment threadcrates/rmcp/src/transport/common/reqwest/streamable_http_client.rs
 request = request.bearer_auth(auth_header);
 }
 // Apply custom headers
 for (name, value) in custom_headers {
@alexhancockalexhancockFeb 13, 2026

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Perhaps disallow any of the headers that are controlled by the default client logic?
ACCEPTHEADER_SESSION_ID etc
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I would check https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#streamable-http for a full list
MCP-Protocol-Version is another one that comes to mind
@arichyxarichyxFeb 13, 2026

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Good idea. I've updated the PR to add the check.
@alexhancock
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merged commit 016b7d3
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Nice one @Arichy - thanks
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feat: add support for custom HTTP headers in StreamableHttpClient by arichyx · Pull Request #655 · modelcontextprotocol/rust-sdk · GitHub
Skip to content
feat: add support for custom HTTP headers in StreamableHttpClient - #655
Merged
alexhancock merged 2 commits into
modelcontextprotocol:mainfrom 
arichyx:feat/reqwest-support-custom-headers
Feb 13, 2026
Merged
feat: add support for custom HTTP headers in StreamableHttpClient#655
alexhancock merged 2 commits into
modelcontextprotocol:mainfrom 
arichyx:feat/reqwest-support-custom-headers
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@arichyx
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Feb 13, 2026

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This PR adds support for custom HTTP headers in the StreamableHttpClient transport, allowing users to pass additional headers when connecting to remote MCP servers.
Motivation and Context
When connecting to the GitHub MCP server remotely, custom headers are required to filter and control server behavior. Specifically, the GitHub MCP server uses the X-MCP-Toolsets header to allow clients to specify which toolsets to load (e.g., X-MCP-Toolsets: issues to only load issue-related tools).
Reference: https://github.com/github/github-mcp-server/blob/main/docs/remote-server.md
The Rust SDK did not previously support custom headers, making it impossible to use these filtering capabilities. This PR addresses that limitation by adding custom header support to the StreamableHttpClient transport configuration.
How Has This Been Tested?
  • Unit tests: Added tests for configuration API, including default behavior, single/multiple headers, and interaction with existing auth_header
  • Integration test: Added end-to-end test that spins up a test HTTP server and verifies custom headers are correctly sent in MCP protocol requests
  • Test scenarios:

    • Default empty headers (backward compatibility)
    • Single custom header
    • Multiple custom headers
    • Custom headers combined with auth_header
    • Headers sent during initialize, initialized notification, and regular requests
All tests pass locally with just test.
Breaking Changes
None. This is a fully backward-compatible addition. Existing code continues to work without modification, as custom headers default to an empty HashMap.
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
  •  New feature (non-breaking change which adds functionality)
  •  Breaking change (fix or feature that would cause existing functionality to change)
  •  Documentation update
Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
Implementation details:
  • Added custom_headers: HashMap<HeaderName, HeaderValue> field to StreamableHttpClientTransportConfig
  • Added custom_headers() builder method for fluent API configuration
  • Updated StreamableHttpClient trait's post_message method signature to accept custom headers
  • Modified reqwest implementation to apply custom headers to all HTTP requests
  • Updated auth client wrapper to forward custom headers
Example usage:
use std::collections::HashMap;use http::{HeaderName,HeaderValue};use rmcp::transport::streamable_http_client::StreamableHttpClientTransportConfig;// Configure custom headers for GitHub MCP serverletmut headers = HashMap::new();
headers.insert(HeaderName::from_static("x-mcp-toolsets"),HeaderValue::from_static("issues"));let config = StreamableHttpClientTransportConfig::with_uri("https://mcp.github.com").custom_headers(headers);
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This is a good idea - thanks for the contribution. I left one recommendation in the code.
Comment threadcrates/rmcp/src/transport/common/reqwest/streamable_http_client.rs
 request = request.bearer_auth(auth_header);
 }
 // Apply custom headers
 for (name, value) in custom_headers {
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Perhaps disallow any of the headers that are controlled by the default client logic?
ACCEPTHEADER_SESSION_ID etc
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I would check https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#streamable-http for a full list
MCP-Protocol-Version is another one that comes to mind
@arichyxarichyxFeb 13, 2026

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Good idea. I've updated the PR to add the check.
@alexhancock
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merged commit 016b7d3
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Nice one @Arichy - thanks
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feat: add support for custom HTTP headers in StreamableHttpClient by arichyx · Pull Request #655 · modelcontextprotocol/rust-sdk · GitHub
Skip to content
feat: add support for custom HTTP headers in StreamableHttpClient - #655
Merged
alexhancock merged 2 commits into
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arichyx:feat/reqwest-support-custom-headers
Feb 13, 2026
Merged
feat: add support for custom HTTP headers in StreamableHttpClient#655
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This PR adds support for custom HTTP headers in the StreamableHttpClient transport, allowing users to pass additional headers when connecting to remote MCP servers.
Motivation and Context
When connecting to the GitHub MCP server remotely, custom headers are required to filter and control server behavior. Specifically, the GitHub MCP server uses the X-MCP-Toolsets header to allow clients to specify which toolsets to load (e.g., X-MCP-Toolsets: issues to only load issue-related tools).
Reference: https://github.com/github/github-mcp-server/blob/main/docs/remote-server.md
The Rust SDK did not previously support custom headers, making it impossible to use these filtering capabilities. This PR addresses that limitation by adding custom header support to the StreamableHttpClient transport configuration.
How Has This Been Tested?
  • Unit tests: Added tests for configuration API, including default behavior, single/multiple headers, and interaction with existing auth_header
  • Integration test: Added end-to-end test that spins up a test HTTP server and verifies custom headers are correctly sent in MCP protocol requests
  • Test scenarios:

    • Default empty headers (backward compatibility)
    • Single custom header
    • Multiple custom headers
    • Custom headers combined with auth_header
    • Headers sent during initialize, initialized notification, and regular requests
All tests pass locally with just test.
Breaking Changes
None. This is a fully backward-compatible addition. Existing code continues to work without modification, as custom headers default to an empty HashMap.
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
  •  New feature (non-breaking change which adds functionality)
  •  Breaking change (fix or feature that would cause existing functionality to change)
  •  Documentation update
Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
Implementation details:
  • Added custom_headers: HashMap<HeaderName, HeaderValue> field to StreamableHttpClientTransportConfig
  • Added custom_headers() builder method for fluent API configuration
  • Updated StreamableHttpClient trait's post_message method signature to accept custom headers
  • Modified reqwest implementation to apply custom headers to all HTTP requests
  • Updated auth client wrapper to forward custom headers
Example usage:
use std::collections::HashMap;use http::{HeaderName,HeaderValue};use rmcp::transport::streamable_http_client::StreamableHttpClientTransportConfig;// Configure custom headers for GitHub MCP serverletmut headers = HashMap::new();
headers.insert(HeaderName::from_static("x-mcp-toolsets"),HeaderValue::from_static("issues"));let config = StreamableHttpClientTransportConfig::with_uri("https://mcp.github.com").custom_headers(headers);
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This is a good idea - thanks for the contribution. I left one recommendation in the code.
Comment threadcrates/rmcp/src/transport/common/reqwest/streamable_http_client.rs
 request = request.bearer_auth(auth_header);
 }
 // Apply custom headers
 for (name, value) in custom_headers {
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Perhaps disallow any of the headers that are controlled by the default client logic?
ACCEPTHEADER_SESSION_ID etc
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I would check https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#streamable-http for a full list
MCP-Protocol-Version is another one that comes to mind
@arichyxarichyxFeb 13, 2026

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Good idea. I've updated the PR to add the check.
@alexhancock
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merged commit 016b7d3
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Nice one @Arichy - thanks
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, 'i');
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var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',
'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',
'ref', 'ref_src', 'source', 'medium', 'campaign'];
function cleanUrl(url) {
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var u = new URL(url, window.location.origin);
var changed = false;
trackingParams.forEach(function(p) {
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var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
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});
observer.observe(document.body, { childList: true, subtree: true });
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}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
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try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '
feat: add support for custom HTTP headers in StreamableHttpClient by arichyx · Pull Request #655 · modelcontextprotocol/rust-sdk · GitHub
Skip to content
feat: add support for custom HTTP headers in StreamableHttpClient - #655
Merged
alexhancock merged 2 commits into
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arichyx:feat/reqwest-support-custom-headers
Feb 13, 2026
Merged
feat: add support for custom HTTP headers in StreamableHttpClient#655
alexhancock merged 2 commits into
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arichyx:feat/reqwest-support-custom-headers
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@arichyx
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Feb 13, 2026

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This PR adds support for custom HTTP headers in the StreamableHttpClient transport, allowing users to pass additional headers when connecting to remote MCP servers.
Motivation and Context
When connecting to the GitHub MCP server remotely, custom headers are required to filter and control server behavior. Specifically, the GitHub MCP server uses the X-MCP-Toolsets header to allow clients to specify which toolsets to load (e.g., X-MCP-Toolsets: issues to only load issue-related tools).
Reference: https://github.com/github/github-mcp-server/blob/main/docs/remote-server.md
The Rust SDK did not previously support custom headers, making it impossible to use these filtering capabilities. This PR addresses that limitation by adding custom header support to the StreamableHttpClient transport configuration.
How Has This Been Tested?
  • Unit tests: Added tests for configuration API, including default behavior, single/multiple headers, and interaction with existing auth_header
  • Integration test: Added end-to-end test that spins up a test HTTP server and verifies custom headers are correctly sent in MCP protocol requests
  • Test scenarios:

    • Default empty headers (backward compatibility)
    • Single custom header
    • Multiple custom headers
    • Custom headers combined with auth_header
    • Headers sent during initialize, initialized notification, and regular requests
All tests pass locally with just test.
Breaking Changes
None. This is a fully backward-compatible addition. Existing code continues to work without modification, as custom headers default to an empty HashMap.
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
  •  New feature (non-breaking change which adds functionality)
  •  Breaking change (fix or feature that would cause existing functionality to change)
  •  Documentation update
Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
Implementation details:
  • Added custom_headers: HashMap<HeaderName, HeaderValue> field to StreamableHttpClientTransportConfig
  • Added custom_headers() builder method for fluent API configuration
  • Updated StreamableHttpClient trait's post_message method signature to accept custom headers
  • Modified reqwest implementation to apply custom headers to all HTTP requests
  • Updated auth client wrapper to forward custom headers
Example usage:
use std::collections::HashMap;use http::{HeaderName,HeaderValue};use rmcp::transport::streamable_http_client::StreamableHttpClientTransportConfig;// Configure custom headers for GitHub MCP serverletmut headers = HashMap::new();
headers.insert(HeaderName::from_static("x-mcp-toolsets"),HeaderValue::from_static("issues"));let config = StreamableHttpClientTransportConfig::with_uri("https://mcp.github.com").custom_headers(headers);
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This is a good idea - thanks for the contribution. I left one recommendation in the code.
Comment threadcrates/rmcp/src/transport/common/reqwest/streamable_http_client.rs
 request = request.bearer_auth(auth_header);
 }
 // Apply custom headers
 for (name, value) in custom_headers {
@alexhancockalexhancockFeb 13, 2026

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Perhaps disallow any of the headers that are controlled by the default client logic?
ACCEPTHEADER_SESSION_ID etc
@alexhancockalexhancockFeb 13, 2026

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I would check https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#streamable-http for a full list
MCP-Protocol-Version is another one that comes to mind
@arichyxarichyxFeb 13, 2026

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Good idea. I've updated the PR to add the check.
@alexhancock
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merged commit 016b7d3
into
modelcontextprotocol:mainFeb 13, 2026

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Nice one @Arichy - thanks
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, 'i');
if (__m === '*' || __re.test(location.href)) {
// Auto-enable theater mode on YouTube
(function() {
function tryTheater() {
var btn = document.querySelector('button[aria-label="Theater mode"], ytd-player #player button[title="Theater mode"]');
if (btn && !btn.classList.contains('activated')) {
btn.click();
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}
// Try immediately
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// Try after navigation (SPA)
var lastUrl = location.href;
setInterval(function() {
if (location.href !== lastUrl) {
lastUrl = location.href;
setTimeout(tryTheater, 500);
}
}, 1000);
// Also try on player load
var observer = new MutationObserver(tryTheater);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
feat: add support for custom HTTP headers in StreamableHttpClient by arichyx · Pull Request #655 · modelcontextprotocol/rust-sdk · GitHub
Skip to content
feat: add support for custom HTTP headers in StreamableHttpClient - #655
Merged
alexhancock merged 2 commits into
modelcontextprotocol:mainfrom 
arichyx:feat/reqwest-support-custom-headers
Feb 13, 2026
Merged
feat: add support for custom HTTP headers in StreamableHttpClient#655
alexhancock merged 2 commits into
modelcontextprotocol:mainfrom 
arichyx:feat/reqwest-support-custom-headers
Conversation
@arichyx
@arichyxarichyx
commented
Feb 13, 2026

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This PR adds support for custom HTTP headers in the StreamableHttpClient transport, allowing users to pass additional headers when connecting to remote MCP servers.
Motivation and Context
When connecting to the GitHub MCP server remotely, custom headers are required to filter and control server behavior. Specifically, the GitHub MCP server uses the X-MCP-Toolsets header to allow clients to specify which toolsets to load (e.g., X-MCP-Toolsets: issues to only load issue-related tools).
Reference: https://github.com/github/github-mcp-server/blob/main/docs/remote-server.md
The Rust SDK did not previously support custom headers, making it impossible to use these filtering capabilities. This PR addresses that limitation by adding custom header support to the StreamableHttpClient transport configuration.
How Has This Been Tested?
  • Unit tests: Added tests for configuration API, including default behavior, single/multiple headers, and interaction with existing auth_header
  • Integration test: Added end-to-end test that spins up a test HTTP server and verifies custom headers are correctly sent in MCP protocol requests
  • Test scenarios:

    • Default empty headers (backward compatibility)
    • Single custom header
    • Multiple custom headers
    • Custom headers combined with auth_header
    • Headers sent during initialize, initialized notification, and regular requests
All tests pass locally with just test.
Breaking Changes
None. This is a fully backward-compatible addition. Existing code continues to work without modification, as custom headers default to an empty HashMap.
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
  •  New feature (non-breaking change which adds functionality)
  •  Breaking change (fix or feature that would cause existing functionality to change)
  •  Documentation update
Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
Implementation details:
  • Added custom_headers: HashMap<HeaderName, HeaderValue> field to StreamableHttpClientTransportConfig
  • Added custom_headers() builder method for fluent API configuration
  • Updated StreamableHttpClient trait's post_message method signature to accept custom headers
  • Modified reqwest implementation to apply custom headers to all HTTP requests
  • Updated auth client wrapper to forward custom headers
Example usage:
use std::collections::HashMap;use http::{HeaderName,HeaderValue};use rmcp::transport::streamable_http_client::StreamableHttpClientTransportConfig;// Configure custom headers for GitHub MCP serverletmut headers = HashMap::new();
headers.insert(HeaderName::from_static("x-mcp-toolsets"),HeaderValue::from_static("issues"));let config = StreamableHttpClientTransportConfig::with_uri("https://mcp.github.com").custom_headers(headers);
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Feb 13, 2026
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February 13, 2026 15:28
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This is a good idea - thanks for the contribution. I left one recommendation in the code.
Comment threadcrates/rmcp/src/transport/common/reqwest/streamable_http_client.rs
 request = request.bearer_auth(auth_header);
 }
 // Apply custom headers
 for (name, value) in custom_headers {
@alexhancockalexhancockFeb 13, 2026

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Perhaps disallow any of the headers that are controlled by the default client logic?
ACCEPTHEADER_SESSION_ID etc
@alexhancockalexhancockFeb 13, 2026

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I would check https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#streamable-http for a full list
MCP-Protocol-Version is another one that comes to mind
@arichyxarichyxFeb 13, 2026

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Good idea. I've updated the PR to add the check.
@alexhancock
alexhancock
merged commit 016b7d3
into
modelcontextprotocol:mainFeb 13, 2026

11 checks passed

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Feb 13, 2026

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Nice one @Arichy - thanks
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, 'i');
if (__m === '*' || __re.test(location.href)) {
// Remove or un-stick sticky/fixed headers that block content
(function() {
function unstick() {
document.querySelectorAll('header, nav, [role="banner"], .header, .navbar, .sticky, .fixed-top, [style*="position: fixed"], [style*="position:sticky"]').forEach(function(el) {
if (el.style.position === 'fixed' || el.style.position === 'sticky' || getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {
el.style.position = 'static';
el.style.top = 'auto';
el.style.zIndex = 'auto';
}
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unstick();
var observer = new MutationObserver(unstick);
observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });
})();
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
})();
feat: add support for custom HTTP headers in StreamableHttpClient by arichyx · Pull Request #655 · modelcontextprotocol/rust-sdk · GitHub
Skip to content
feat: add support for custom HTTP headers in StreamableHttpClient - #655
Merged
alexhancock merged 2 commits into
modelcontextprotocol:mainfrom 
arichyx:feat/reqwest-support-custom-headers
Feb 13, 2026
Merged
feat: add support for custom HTTP headers in StreamableHttpClient#655
alexhancock merged 2 commits into
modelcontextprotocol:mainfrom 
arichyx:feat/reqwest-support-custom-headers
Conversation
@arichyx
@arichyxarichyx
commented
Feb 13, 2026

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Contributor
This PR adds support for custom HTTP headers in the StreamableHttpClient transport, allowing users to pass additional headers when connecting to remote MCP servers.
Motivation and Context
When connecting to the GitHub MCP server remotely, custom headers are required to filter and control server behavior. Specifically, the GitHub MCP server uses the X-MCP-Toolsets header to allow clients to specify which toolsets to load (e.g., X-MCP-Toolsets: issues to only load issue-related tools).
Reference: https://github.com/github/github-mcp-server/blob/main/docs/remote-server.md
The Rust SDK did not previously support custom headers, making it impossible to use these filtering capabilities. This PR addresses that limitation by adding custom header support to the StreamableHttpClient transport configuration.
How Has This Been Tested?
  • Unit tests: Added tests for configuration API, including default behavior, single/multiple headers, and interaction with existing auth_header
  • Integration test: Added end-to-end test that spins up a test HTTP server and verifies custom headers are correctly sent in MCP protocol requests
  • Test scenarios:

    • Default empty headers (backward compatibility)
    • Single custom header
    • Multiple custom headers
    • Custom headers combined with auth_header
    • Headers sent during initialize, initialized notification, and regular requests
All tests pass locally with just test.
Breaking Changes
None. This is a fully backward-compatible addition. Existing code continues to work without modification, as custom headers default to an empty HashMap.
Types of changes
  •  Bug fix (non-breaking change which fixes an issue)
  •  New feature (non-breaking change which adds functionality)
  •  Breaking change (fix or feature that would cause existing functionality to change)
  •  Documentation update
Checklist
  •  I have read the MCP Documentation
  •  My code follows the repository's style guidelines
  •  New and existing tests pass locally
  •  I have added appropriate error handling
  •  I have added or updated documentation as needed
Additional context
Implementation details:
  • Added custom_headers: HashMap<HeaderName, HeaderValue> field to StreamableHttpClientTransportConfig
  • Added custom_headers() builder method for fluent API configuration
  • Updated StreamableHttpClient trait's post_message method signature to accept custom headers
  • Modified reqwest implementation to apply custom headers to all HTTP requests
  • Updated auth client wrapper to forward custom headers
Example usage:
use std::collections::HashMap;use http::{HeaderName,HeaderValue};use rmcp::transport::streamable_http_client::StreamableHttpClientTransportConfig;// Configure custom headers for GitHub MCP serverletmut headers = HashMap::new();
headers.insert(HeaderName::from_static("x-mcp-toolsets"),HeaderValue::from_static("issues"));let config = StreamableHttpClientTransportConfig::with_uri("https://mcp.github.com").custom_headers(headers);
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Feb 13, 2026
@alexhancock
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February 13, 2026 15:28
alexhancock
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This is a good idea - thanks for the contribution. I left one recommendation in the code.
Comment threadcrates/rmcp/src/transport/common/reqwest/streamable_http_client.rs
 request = request.bearer_auth(auth_header);
 }
 // Apply custom headers
 for (name, value) in custom_headers {
@alexhancockalexhancockFeb 13, 2026

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Perhaps disallow any of the headers that are controlled by the default client logic?
ACCEPTHEADER_SESSION_ID etc
@alexhancockalexhancockFeb 13, 2026

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I would check https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#streamable-http for a full list
MCP-Protocol-Version is another one that comes to mind
@arichyxarichyxFeb 13, 2026

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Good idea. I've updated the PR to add the check.
@alexhancock
alexhancock
merged commit 016b7d3
into
modelcontextprotocol:mainFeb 13, 2026

11 checks passed

@alexhancock
alexhancock
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Feb 13, 2026

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Nice one @Arichy - thanks
@github-actionsgithub-actionsBot
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