Description
Since approximately May 18, 2026 (coinciding with v1.0.5 release), the remote MCP endpoint at https://api.githubcopilot.com/mcp/ intermittently returns HTTP 500 with a raw text/plain error body. The failure rate is approximately 7–10% and affects write operations like create_branch. Read-only operations (search_repositories, get_file_contents) appear unaffected.
Error Response
HTTP Status: 500 Internal Server Error
Content-Type: text/plain; charset=utf-8 (not a valid JSON-RPC or SSE response)
can't get copilot user by id: error getting copilot user details: twirp error permission_denied: Error from intermediary with HTTP status code 403 "Forbidden"
Full Request/Response Context
Request:
POST https://api.githubcopilot.com/mcp/
Authorization: Bearer <valid-PAT-with-repo-scope>
Content-Type: application/json
Accept: application/json, text/event-stream
Mcp-Session-Id: <valid-session-id>
{
"jsonrpc": "2.0",
"method": "tools/call",
"id": 9,
"params": {
"name": "create_branch",
"arguments": {
"owner": "<org>",
"repo": "<private-repo>",
"branch": "test-branch-name",
"from_branch": "main"
}
}
}Response Headers:
HTTP/2 500
content-type: text/plain; charset=utf-8
x-github-backend: Kubernetes
x-github-request-id: D44E:1D706B:5F7B92F:675BE79:6A0C6556
Reproduction
- Frequency: ~7–10% of
create_branch calls (1 in 9 to 1 in 15 attempts)
- Pattern: Random, not correlated with request timing or concurrency
- Session state: Occurs on freshly initialized sessions (not stale session issue)
- Authentication: PAT is valid (other calls in the same session succeed;
initialize and tools/list always return 200)
Minimal reproduction: send 15–30 consecutive create_branch tool calls (each with a new session). Typically 1–3 will return HTTP 500.
Analysis
The error chain suggests the failure occurs in the Copilot hosting infrastructure (not in the open-source MCP server logic):
- Request passes HTTP gateway authentication (PAT is valid → not 401)
- Hosting layer attempts internal twirp RPC:
getCopilotUserById
- An internal service mesh intermediary returns 403 Forbidden to the twirp call
- This unhandled error propagates as a raw HTTP 500 to the client
The 403 from the "intermediary" indicates a service-to-service authentication failure (likely mTLS cert rotation, internal token expiry, or inconsistent sidecar state during deployment), not a user-permission issue.
Impact
- MCP clients using
streamablehttp_client have their entire transport killed by this error (the SDK's post_writer TaskGroup crashes, closing read/write streams)
- Simple in-session retries are ineffective because the session is dead after the 500
- Automated workloads (CI/CD, evaluation pipelines) see cascading failures
Expected Behavior
- HTTP 500 should not leak internal error details to clients
- The
getCopilotUserById lookup should have retry/circuit-breaker logic on the server side
- Alternatively, the error should be wrapped in a proper JSON-RPC error response so MCP clients can handle it gracefully
Environment
- MCP Protocol Version:
2024-11-05
- Transport: Streamable HTTP (POST)
- Client: Python MCP SDK (
mcp package)
- Authentication: GitHub PAT (repo + read:org scopes)
- GitHub MCP Server version: v1.0.5 (remote, hosted)
Related
Description
Since approximately May 18, 2026 (coinciding with v1.0.5 release), the remote MCP endpoint at
https://api.githubcopilot.com/mcp/intermittently returns HTTP 500 with a raw text/plain error body. The failure rate is approximately 7–10% and affects write operations likecreate_branch. Read-only operations (search_repositories,get_file_contents) appear unaffected.Error Response
HTTP Status:
500 Internal Server ErrorContent-Type:
text/plain; charset=utf-8(not a valid JSON-RPC or SSE response)Full Request/Response Context
Request:
{ "jsonrpc": "2.0", "method": "tools/call", "id": 9, "params": { "name": "create_branch", "arguments": { "owner": "<org>", "repo": "<private-repo>", "branch": "test-branch-name", "from_branch": "main" } } }Response Headers:
Reproduction
create_branchcalls (1 in 9 to 1 in 15 attempts)initializeandtools/listalways return 200)Minimal reproduction: send 15–30 consecutive
create_branchtool calls (each with a new session). Typically 1–3 will return HTTP 500.Analysis
The error chain suggests the failure occurs in the Copilot hosting infrastructure (not in the open-source MCP server logic):
getCopilotUserByIdThe 403 from the "intermediary" indicates a service-to-service authentication failure (likely mTLS cert rotation, internal token expiry, or inconsistent sidecar state during deployment), not a user-permission issue.
Impact
streamablehttp_clienthave their entire transport killed by this error (the SDK'spost_writerTaskGroup crashes, closing read/write streams)Expected Behavior
getCopilotUserByIdlookup should have retry/circuit-breaker logic on the server sideEnvironment
2024-11-05mcppackage)Related