MCP server failed to start or connect — page 2
A configured MCP server never completed its handshake or dropped out.
230 issues · 46 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. 61 new reports in the last 90 days vs 89 in the 90 before — -31%. The open backlog peaked at 46 in 2026-08 and sits at 46 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
137 of these reports name the Claude Code build they were running, spanning 85 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 101–200
Ranked by community engagement (reactions weighted over comments).
- [BUG] Windows: npx-based MCP/plugin servers fail to connect (spawn EINVAL from .cmd shim)
- /mcp reconnect after config-hash-stale spawns literal unexpanded ${CLAUDE_PLUGIN_ROOT} → -32000
- [BUG] Slack MCP slack_read_file fails with invalid_union content validation error (content[1]) for binary files
- [BUG] Auto-update orphans MCP child processes on Windows, breaking next launch of npx-based MCP servers (EBUSY)
- [BUG] CLI crashes (exit code 1) on unhandled McpError -32001 AbortError during tool_use
- Claude Code goes silent for 10+ minutes in status=requesting after a tool_result with is_error=true
- "Unhandled case: [object Object]" overlay crashes session (correlates with MCP SSE reconnect)
- claude.ai Figma connector loaded by VSCode extension despite being disabled in web + Desktop + /mcp UI (Max plan)
- VSCode extension v2.1.141 renders 'Unhandled case: [object Object]' instead of MCP server error messages
- Bun runtime SIGKILL's stdio MCP server process group after ~60s idle
- Remote MCP (Figma): post-OAuth reconnect hangs 30s and fails, requires full restart
- [BUG] MCP tool result spuriously reports "user denied" without showing a permission prompt — affects mcp__codebrain__reindex_codebaseandmcp__codebrain__save_memory mid-session
- [BUG] `claude --print -p` silently exits 143 after ~14 tool round-trips
- [BUG] Cowork dispatches macOS-only extensions to Linux remote → retry loop causes remote OOM and local renderer leak
- Slack MCP (mcp.slack.com) fails: does not support dynamic client registration
- Slack MCP (mcp.slack.com) fails: does not support dynamic client registration
- HTTP MCP servers returning 405 on GET health check fail to load tools at session startup
- MCP stdio transport to plugin silently dies, no disconnect/error logged
- [Bug] plugin:slack OAuth flow never triggers — SSE endpoint 302-redirects instead of returning 401
- [Bug] Plugin sync fails to extract scripts directory from bundle, breaking local MCP servers
- [Bug] Export functionality fails when attempting both clipboard and file output simultaneously
- [Bug] Non-Opus models consume tokens when only Opus 4.6 specified
- MCP elicitation queue leaks on abort — multi-elicit tool calls silently stall
- [Bug] CLI hangs with active timers while token processing stalls
- [BUG] timeout field in claude_desktop_config.json not honored for MCP servers
- [BUG] Excessive usage from stalled API streams + silent thinking token consumption
- [BUG] MCP OAuth: Client does not fall back to OIDC Discovery (/.well-known/openid-configuration) when RFC 8414 metadata returns 404
- Claude in Chrome: CLI MCP client fails to connect despite working native messaging and socket (macOS, multi-profile)
- [BUG]
- MCP servers fail silently on session start with no auto-recovery or health feedback
- [BUG] Gmail MCP fails — npm package @anthropic-ai/google-gmail-mcp returns 404
- MCP servers with many tools silently fail to connect on startup
- stdio MCP servers fail to connect — process never spawned
- GitHub Copilot HTTP MCP server fails to reconnect after remove/re-add
- [BUG] MCP Server Connection Fails on Windows — `cmd /c` wrapper corrupted by CLI parser
- VSCode extension MCP panel shows "X Failed" for github server that is actually connected
- BUG: claude-in-chrome MCP fails - npm package @anthropic-ai/claude-in-chrome-mcp not published (404)
- OAuth MCP servers fail in remote-control mode due to disabled redirect handling
- [Bug] Bash allow rule glob pattern fails to match commands with multiline command substitution containing heredocs
- [BUG]
- [Bug] stdio MCP server stdin closed before initialize request on startup
- MCP stdio server fails on Windows with libuv assertion crash
- Claude Desktop v1.1.4173 crashes on startup: @formatjs/intl unhandled rejection
- MCP server connection fails silently on VS Code extension startup
- [BUG] MCP Atlassian OAuth tokens stored but not retrieved for SSE connection (400 error)
- MCP HTTP transport ignores configured URL path, defaults to /sse
- [BUG] Slack MCP connector fails to authenticate - SSE OAuth flow broken + GitHub PAT undocumented
- [BUG] macOs - Claude consumes massive diskspace (472GB) in ~/.claude/debug and ~/Library/Caches/claude-cli-nodejs/<project>/--mcp-logs-*
- [BUG] HTTP MCP connection fails with Snap Lens Studio - protocol version mismatch (2024-11-05 vs 2025-06-18)
- [Bug] Claude consumes tokens and responds after manual background task termination
- [BUG] MCP Server Connection Race Condition - Connections closed immediately after establishment
- HTTP MCP Server "Failed to connect" Despite Successful Manual Testing
- [BUG] C# MCP Server stdio transport fails to connect - health check timeout issue
- [BUG] MCP Connection Status Shows "Failed to Connect" Despite Working Server (Protocol Violation in Health Checker)
- [BUG] MCP is broken ENOENT on MacOS
- JSON Parsing Error: Invalid Low Surrogate in Request Body
- [BUG] timeout makes you loose session
- [BUG] Claude Code, Linux, v1.0.51, node.js exception
- Unhandled MCP Connection Closed Error in WebSocket Transport
- /mcp command fails with timeout and claude doctor shows "Raw mode is not supported" error
- Windows: CCD session host repeatedly exits killing live background tasks ('torn down with N live background task(s)') — Desktop 1.37937.3 / runtime 2.1.246, filesystem MCP relay flapping
- claude.ai META mcp connector times out in Claude Code CLI while working in claude.ai web chat
- Built-in design MCP (claude_design) auto-injected and 401s even when frontend-design plugin is disabled
- [BUG] stdio MCP tool call hangs indefinitely under `claude -p` when the full MCP fleet is loaded — regression in 2.1.177, works under --strict-mcp-config
- [BUG] ArchicadTapir MCP server consistently fails to connect on startup with "Could not attach to MCP server ArchicadTapir"
- [Bug] MCP Server Connection Failed in `/doctor` Command
- MCP stdio server fails to start at session init with no error surfaced (silent no-spawn)
- `claude mcp list` prints expanded `${ENV}` values in plain text, leaking secrets to terminal/scrollback/ps
- Built-in "claude.ai Figma" connector shows "Failed to connect" instead of "Needs authentication"
- [Feature Request] Restore claude -p support or provide alternative pricing for agentic workflows
- Meta Ads MCP at mcp.facebook.com/ads rejects Claude Code CLI OAuth — redirect_uris not registered
- Compact context 因 MCP 服务启动失败而中止，仅执行 1 步后停止
- [Feature Request] Add ability to cancel scheduled wakeups
- [DOCS] MCP docs missing startup auto-retry behavior for transient errors
- [Bug] Terminal output exceeds viewport width, requires scrolling to view complete responses
- [Bug] Response streaming duplicates and drops content
- [BUG] Claude Desktop MCP tool calls silently timeout after 4min on Windows — affects ALL transports, causes UI state corruption
- Plugin-bundled MCP servers should be opt-in, not fail-loudly on every startup
- [BUG] Cowork times out attaching a minimal local .mcpb extension
- HTTP MCP transport fails to connect to Cypress Cloud MCP server (missing Accept header)
- MCP HTTP+OAuth fails: Claude Code sends unrecognised 'elicitation.form' capability field causing -32603 on older Java MCP SDKs
- CCD/Cowork requires system Node.js for local MCP extensions while Chat uses built-in UtilityProcess
- HTTP MCP servers with OAuth don't trigger browser auth flow
- [Bug] /new command not recognized when issued by user in conversation
- [Bug] AskUserQuestion tool auto-answers without showing interactive UI in v2.1.63
- [BUG] Agent Teams: Catastrophic agent lifecycle failures, duplicate spawning, and mailbox polling waste
- [BUG] AWS MCP proxy (mcp-proxy-for-aws) fails during initialization with -32602: Invalid request parameters
- [Bug] MCP HTTP Transport: JSON-RPC validation paradox - rejects valid jsonrpc: 2.0
- Feature Request: Include error details in mcpServerStatus() response
- [Bug] Claude Code hangs indefinitely without progress
- [Feature Request] Support mTLS Client Certificates for SSE MCP Transport
- Unhandled Promise Rejection: MCP Connection Closed Error
- [BUG] non-interactive mcp add doesn't accept arguments
- [BUG] mcp add incorrectly escapes command line arguments
- [BUG] Windows: one broken MCP server entry in claude_desktop_config.json silently kills every cold session start (no turn, worker exits) — should degrade gracefully
- [BUG] Cowork local MCPB calls fail with -32003 without approval UI, even in Skip mode
- [BUG] MCP streamable-HTTP: an immediate 404 "Session not found" is surfaced as -32001 Request timed out, the session is never re-initialized, and the call is silently lost
- [plugin: telegram] Concurrent sessions race on bun install, MCP server fails to start (EEXIST -> -32000 Connection closed)
- [Bug] MCP connector startup starvation with large unauthenticated connector pools causes -32001 timeouts
- [BUG] Linux native binary: MCP HTTPS fails UNKNOWN_CERTIFICATE_VERIFICATION_ERROR for chains anchored on roots newer than the embedded bundle; CLAUDE_CODE_CERT_STORE has no effect