MCP server failed to start or connect
A configured MCP server never completed its handshake or dropped out.
229 issues · 45 open · 184 resolved (80%) · first seen Mar 5, 2025
First response · integration
What to do now
Most likely: A local integration or child process did not satisfy Claude Code’s expected contract.
- Isolate the failing MCP server, shell command or editor integration.
- Run that dependency directly and capture its exit code and stderr.
- Compare with a clean configuration before editing global settings.
These are conservative triage steps, not an official Anthropic fix. Use the issue and workaround evidence below before making a destructive configuration change.
Is this getting better or worse?
This class of problem is converging. 60 new reports in the last 90 days vs 89 in the 90 before — -33%. The open backlog peaked at 45 in 2026-08 and sits at 45 today.
Derived by counting each matching issue from its creation date until it closed. First-party
computation over the anthropics/claude-code tracker — the trend is not published
anywhere upstream.
Which builds report this
136 of these reports name the Claude Code build they were running, spanning 84 releases. Heaviest reporters:
- Claude Code v2.1.220
- Claude Code v2.1.114
- Claude Code v2.1.63
- Claude Code v2.1.216
- Claude Code v2.1.181
- Claude Code v2.1.141
- Claude Code v2.1.126
- Claude Code v2.1.123
Report volume, not a defect count: an issue can mention a build without that build having caused the failure. Versions come from the version string in the bug-report template, matched against real published tags.
Do these get fixed?
Median time to close is 27 days across 184 closures. Of the 184 closures with a recorded reason, 21% were closed as completed and 146 as not-planned or duplicate. The most recent completed fix landed in 2026-08.
Workarounds reported by the community
78 of these issues post a workaround someone says worked. The highest-engagement ones:
- Claude.ai MCP servers auto-injected into Claude Code without opt-in — causes OOM crashes on resource-constrained systems
- …r's Claude.ai account and load them into every CLI session. Workaround Manually editing to set: However, this is a cached flag and may be overwritten on next update/startup. Expected Behavior 1. This should be opt-in, no…
Found in the description of #20412 · resolved - [BUG] Slack plugin fails to authenticate - "does not support dynamic client registration"
- …blocking real workflow automation for us. Why the bot token workaround ( ) doesn't work: - Bot tokens require the bot to be invited to every channel. In an enterprise workspace with dozens of relevant channels, this is i…
Found in the thread of #18009 · resolved - [FEATURE] Claude can reconnect to a broken MCP in a manner similar to how it performs other actions
- …call pauses the conversation rather than letting the model work around it. Together with the reconnection UX proposed in this issue, the behavior tiers would be: Scenario Action ---------- -------- Server process crashe…
Found in the thread of #10071 · still open - [BUG] Claude Code SDK: SDK MCP server faills to connect due to closed stream
- I encountered the same issue today and was able to work around it with a minimal adjustment: 1. Refactored into an MCP Server using (this was straightforward since the code format is nearly identical). 2. Updated the def…
Found in the thread of #6710 · resolved - [BUG] OAuth Authentication Succeeds but MCP Reconnection Fails - Requires Restart
- …ansport - Server is properly configured for streamable-http Workaround Restart Claude Code after OAuth authentication completes. The stored tokens are preserved and work correctly after restart. Impact - Poor user experi…
Found in the description of #10250 · resolved
Excerpts are quoted from the linked issue so you can judge relevance before opening it. Threads that only ask for a workaround, or report that there is none, are excluded. These are community suggestions, not official guidance from Anthropic — read the full thread before applying one.
Matching issues 1–100
Ranked by community engagement (reactions weighted over comments).
- Claude.ai MCP servers auto-injected into Claude Code without opt-in — causes OOM crashes on resource-constrained systems
- [BUG] Slack plugin fails to authenticate - "does not support dynamic client registration"
- [FEATURE] Claude can reconnect to a broken MCP in a manner similar to how it performs other actions
- BUG: MCP servers fail to connect in Claude Code despite correct configuration
- [BUG] Claude Code SDK: SDK MCP server faills to connect due to closed stream
- [BUG] OAuth Authentication Succeeds but MCP Reconnection Fails - Requires Restart
- [BUG] Claude code does not obey values of MCP_TIMEOUT longer than 60 seconds
- claude_design MCP fails: 404 from api.anthropic.com/v1/design/mcp (harness-injected, unremovable)
- [BUG] Slack MCP "Failed to connect" — cannot reconnect after re-authentication
- Xcode MCP tools requiring Automation permission hang indefinitely for CLI clients without bundle identifiers
- [BUG] Omits OAuth resource parameter required by MCP 2025-06-18
- [Bug] Plan mode not enforced; tool calls continue despite plan-mode indicator
- [BUG] MCP server connection fails with error -32000: Connection closed (race condition)
- [BUG] Claude Code fails to resolve Git Bash path with space in Windows (`Program Files`)
- [BUG] Remote sentry mcp is not launching auth flow
- JIRA Integration Fails in Claude Code with Authentication Error
- [BUG] MCP HTTP client doesn't re-initialize session after "Server not initialized" error
- [BUG] Unable to connect to MCP Server when using HTTP PROXY.
- [BUG] Windows: Atlassian Remote MCP Server fails to connect
- Playwright MCP Initialization Fails on First Install Requiring Manual Restart
- [BUG] MCP HTTP server connection fails in v2.1.84+ when server uses stateless transport (GET /mcp returns 405)
- [Bug] Code tab only displays GitHub connection screen after remote session exit
- MCP error -32000: Connection closed - Node.js uncaught exception
- UI shows "Unhandled case: [object Object]" toast when SDK stream ends with error after stall
- Elicitation hooks not triggered with --input-format stream-json
- [BUG] MCP Fails on native Windows
- [BUG] Custom MCP connector OAuth tokens fail to persist across restart; menu "Connect" silently fails while in-chat auth works
- [BUG] npx MCP servers fail to load after "claude update"
- Brave Search MCP Server Installation Error
- MCP server "ide" connection fails immediately on startup - IntelliJ IDEA plugin 0.1.14-beta
- [BUG] Cursor IDE integration fails: option disappears after brief availability
- Unhandled MCP Connection Closed Error in Claude Code CLI
- [BUG] Remote (Streamable HTTP) MCP form elicitation never reaches the client: no dialog, no `Elicitation` hook, server times out at -32001
- Remote MCP servers declaring completions/logging capabilities fail to connect despite valid initialize handshake
- [Bug] GitHub MCP Connection Failed
- Late response to cancelled MCP request drops stdio transport instead of being ignored
- MCP stdio transport: client kills stdin 2-5s after receiving successful tool response (chrome-devtools-mcp)
- [BUG] Claude Code CLI MCP connection issue
- [BUG] Notion MCP blocked by proxy in Cowork sessions - mcp.notion.com not on allowlist
- Cost estimation blind spots when building agent systems with Claude Code
- [BUG] Issue with Atlassian MCP
- [BUG] Claude code does not obey values of MCP_TIMEOUT longer than 60 seconds
- [BUG] Prompt cache lookup fails intermittently mid-session — cache_read pinned to the stable-prefix boundary, 89 full-context rewrites across 9 days (~59M excess cache_creation tokens)
- Claude Code 2.1.143 silently hangs MCP tool calls after SSE drop — client logs the drop but does not fail or reconnect
- [BUG] MCP server args containing `~` (tilde) cause ENOENT — tilde not expanded in stdio server arguments
- [Feature Request] Auto-reconnect to MCP servers on connection loss
- [BUG] Windows: MCP server fails with /d: Is a directory -> MCP error -32000: Connection closed
- [MCP servers “Failed to connect” on Windows 11 (Node 22, npm 11.5.1, Claude CLI 1.0.62)]
- Connection Failure: Sentry MCP Network Communication Error
- [BUG] stdio MCP server always times out at ~30000ms on Windows, even though it connects via MCP Inspector)
- [BUG] claude mcp login for the Claude Design MCP server opens a decommissioned /authorize endpoint (HTTP 410), hanging the OAuth flow
- tmux/psmux auto-detection disables session transcript persistence — .jsonl never written
- Gmail / Calendar hosted MCP endpoints (*.mcp.claude.com) return 404 — deprovisioned or outage?
- [BUG] Official Meta Ads MCP (mcp.facebook.com/ads) fails OAuth with "redirect_uris are not registered for this client"
- Stdio MCP server cwd field silently ignored on Windows (2.1.123)
- MCP resource read errors surface as 'Connection closed' instead of the actual JSON-RPC error
- MCP servers using npx fail to connect in VS Code 1.112
- [BUG] MCP servers fail on startup due to race condition — connections dropped before REPL mounts (AlmaLinux 8 / RHEL 8)
- [BUG] SSE MCP connection fails with "Could not convert argument of type symbol to string"
- [BUG] MCP Server Connection Failures on Windows
- [BUG] Unable to connect to stdio MCP proxies from Windows Terminal
- [BUG] CCR proxy returns -32003 needs_approval and the retroactive approval card cannot succeed — root cause analysis from the shipped client (2.1.220)
- [BUG] Cowork/MCP tool calls fail with -32001 after ~60s even when the server completes and the result arrives
- [BUG] Desktop app cancels stdio MCP tool calls at ~60s and ignores MCP_TOOL_TIMEOUT; the CLI honors it
- [BUG] HTTP MCP server returning RFC 6750 401 without RFC 9728 `resource_metadata=` hint surfaces as 'Failed to connect' instead of triggering OAuth dance
- [BUG] Cowork MCP client times out long-running tool calls despite server progress notifications
- MCP servers crash on macOS when accessing Bluetooth — missing NSBluetoothAlwaysUsageDescription in claude-code bundle
- [FEATURE] Need a canonical way for MCP servers (e.g from plugins) to provide startup error messages
- [BUG] MCP server named "supabase" ignores stdio configuration and forces SSE/OAuth connection
- [BUG] Claude Code HTTP MCP Transport - Connection Failure
- [BUG] SSE MCP Server fails to connect to Monday.com despite valid endpoint
- /ide command fails in devcontainer: VS Code extension ignores $CLAUDE_CONFIG_DIR when writing lock files
- MCP Connection Closed Unexpectedly During IDE Interaction
- [RESOLVED - not a CLI bug] Orchestrator SIGTERMed its own agents every 300s; surfaced as aborted_tools with no logged cause
- [BUG] MCP tool calls fail with -32003 after approval on mobile web
- Claude Desktop spawns duplicate generations of local MCP server processes without terminating the previous generation
- Stdio MCP server that exits mid-session: lazy reconnect serves one call, then tools are wrongly deregistered while respawned process leaks
- stdio MCP server tools dropped when initialize exceeds probe timeout
- [Bug] Loop command repeats identical responses instead of progressing to next steps
- [Bug] Auto-mode prevents basic function execution
- [Feature Request] Allow runtime preference customization for rejected commands in auto mode
- [BUG] Claude ignores user's MEMORY.md and auto-memory files during debugging — treats external memory as disposable
- [BUG] Cowork silently drops uvx-based plugin MCP servers — startup timeout too short for PyPI cold-start
- [Channels] onSubmit early return due to "suggestions showing" causes input to silently disappear
- [Bug] Claude Code: Inconsistent or unreliable response behavior
- npx-based MCP plugins (Playwright, Context7) fail to connect with concurrent sessions
- [BUG] Claude Code MCP does not use the NO_PROXY setting in environment variables
- [BUG] MCP server spawning fails for some .bat/.cmd files on Windows
- [Bug] Chrome Extension MCP Connection Failed: Agent Cannot Access Chrome Tools
- Bug: Claude Code times out on USB tethering + VPN (Windows)
- [BUG] Initialization delay causes resources/list and prompts/list timeout
- [Feature Request] Make MCP tool timeouts configurable in Claude Desktop
- [BUG] Can not connect to MCP servers running by `pnpx` in Windows
- Connection Closed Unexpectedly During Claude Code Interaction
- HTTP MCP: valid token treated as expired — "OAuth session expired and could not be refreshed" when provider issues no refresh token (mcp.facebook.com/ads)
- CLAUDE_PLUGIN_ROOT path separators stripped on Windows-client + WSL-mounted project (semgrep@2.1.1 MCP fails 100%)
- Local stdio MCP server fails with "access denied for socket file" when spawned by MSIX-packaged Claude Desktop on Windows (works fine under Codex on the same machine)
- claude_design connector / /design-login not available
- [Bug] MCP tool call wedges indefinitely without client-side timeout (CLI, no MCP_TOOL_TIMEOUT default)
- [BUG] Desktop extension install silently fails — "Installing unsigned extension" then no completion, no toggle (Autodesk Fusion connector)