Why does Claude Code keep saying the session expired?

This happens when your authentication token becomes invalid, expired, or corrupted. It can also be caused by macOS keychain locks, VPN interference, or OAuth callback timeouts.

How do I reconnect Claude Code?

The fastest way to reconnect is to sign out, clear your cached credentials using 'rm -rf ~/.claude/cache', and then complete the full login flow again.

What is an OAuth callback timeout?

It occurs when the browser takes longer than 60 seconds to pass the authentication token back to the CLI, often due to too many open tabs or a slow network connection.

Why does Claude Code say 'installation failed' but then 'installation complete'?

This contradictory message almost always means a stale lock file exists from a previous interrupted install. The installer aborts due to the lock but then partially completes a different step, giving you two contradictory status messages. Remove the lock file at ~/.local/state/claude/locks/ and reinstall.

I get claude: command not found even after a successful install. What's wrong?

Your terminal session hasn't loaded the updated PATH that the installer added to your shell config. Open a new terminal window, or run source ~/.zshrc (or ~/.bashrc on Linux). If that doesn't work, confirm that npm's global bin directory is actually in your PATH.

Do I need sudo to install Claude Code?

No — and using sudo will likely cause more problems. Set your npm global directory to a user-owned path with npm config set prefix ~/.npm-global, add that to your PATH, and then install without sudo.

Claude Code installation fails with a TLS/SSL error. How do I fix it?

This happens in corporate environments that use SSL inspection. Export your company's CA certificate path: export NODE_EXTRA_CA_CERTS=/path/to/ca.pem. Your IT team can provide the certificate file.

The Claude Code installer just hangs and never completes. What's happening?

A hanging installer almost always means a network block. The installer downloads from storage.googleapis.com. Set your proxy with export HTTPS_PROXY=http://your-proxy:port and retry, or ask IT to whitelist that domain.

I'm on Windows. Should I use npm or the curl installer?

Use PowerShell with npm install -g @anthropic-ai/claude-code. Don't use Git Bash; it lacks TTY support and will cause raw mode errors. If you're in WSL, use the curl installer within your Linux environment.

How do I know if Claude Code installed correctly?

Run claude --version to confirm the binary is accessible, then run claude doctor for a full diagnostic report. Both should return clean results with no errors before you start using the tool in a real project.

Claude Code MCP Server Not Working: Complete Fix Guide

September 2, 2026 by

aliakram

If a Claude Code MCP server won't connect, won't load its tools, or throws an error when you start a session, the fastest path to a fix is to stop guessing and read the actual status Claude Code gives you. Every MCP failure in Claude Code shows one of a handful of specific statuses: Failed to connect, Connection error, Needs authentication, or a server with no tools and each one points to a different cause.

Quick Answer

Run this first, from your terminal (not inside a claude session):

bash

claude mcp list

This shows every configured server and its status. Then run, inside a session:

/mcp

or from your terminal:

bash

claude mcp get <server-name>

Claude mcp prints the error details of an HTTP status code, a missing environment variable, or the exact command Claude Code tried to run. Most "MCP server not working" problems fall into one of these buckets:

The server was added in the wrong project or wrong config file
The server's status is Failed to connect or Connection error (process/network issue)
The server needs authentication you haven't completed
The server connects but registers zero tools (usually a missing API key)
A PATH issue means Claude Code can't find node or npx, even though your terminal can

The sections below match each symptom to its fix.

Symptoms: What "Not Working" Looks Like

MCP problems in Claude Code usually show up as one of these:

Status you see	What it means
No MCP servers configured	Claude Code found no servers for the current directory
✘ Failed to connect	The server didn't respond
✘ Connection error	The connection attempt threw an error
! Needs authentication	Server is reachable but requires sign-in or a token
! Connected · tools fetch failed	Server connected but couldn't list its tools
Server shows connected, tool list is empty	Server started but registered no tools
⏸ Pending approval	A project-scoped server you haven't approved yet

Both Failed to connect and Connection error mean the server didn't start or the URL didn't respond, but they differ in how much detail Claude Code shows — see the diagnosis step below.

Step 1 — Diagnose Before You Fix Anything

Don't start editing config files yet. Run both of these:

bash

claude mcp list

/mcp

For a specific server, get the full error detail with:

bash

claude mcp get <server-name>

This is the single most useful diagnostic command.

Step 2 — Match Your Error to Its Cause

Fix: "No MCP servers configured"

You added the server from a different project. Local-scoped servers are tied to the directory you were in. Re-add from the current project, or use --scope user:

bash

claude mcp add --scope user --transport http my-server https://example.com/mcp

You edited a config file at the wrong path. Claude Code only reads two files:

Scope	File	Available to
local (default)	~/.claude.json, under the project entry	Only you, only this project
project	.mcp.json in the project root	Everyone who clones the project
user	~/.claude.json, top-level mcpServers key	Only you, all projects

It does not read ~/.claude/settings.json, ~/.claude/mcp_servers.json, or %APPDATA%\Claude\mcp.json.

A malformed entry in .mcp.json. Claude Code silently skips broken entries. Run claude mcp list and check for a parse warning.

Fix: "Failed to connect" or "Connection error"

Failed to connect: claude mcp list/claude mcp get <name> show the HTTP status or error text (v2.1.219+).
Connection error: no extra detail on any version — go straight to manual checks.

HTTP/hosted servers — confirm reachability:

bash

curl -I https://mcp.example.com

404/405 → server is up (many endpoints only answer POST); a 404 usually means the wrong path — compare claude mcp get <name>'s URL to the server's documented endpoint.
401/403 → server is up, needs auth.
No response → check the URL and network.

Local (stdio) servers — run the exact command yourself:

bash

npx -y @playwright/mcp@latest

Starts and waits → server works; compare the command in claude mcp get <name> to what you typed — if it differs, you likely omitted the -- separator.
Errors immediately → the message usually names what's missing.

Fix: "Needs authentication"

Run /mcp, select the server, choose Authenticate. On v2.1.186+, you can also run:

bash

claude mcp login my-server
claude mcp login my-server --no-browser      # no local browser
claude mcp login my-server --callback-port 8080   # fixed redirect URI
claude mcp logout my-server && claude mcp login my-server   # force fresh sign-in

The bearer-token trap: for static-token servers:

bash

claude mcp add --transport http my-server https://mcp.example.com --header "Authorization: Bearer YOUR_TOKEN"

If the server rejects that header, Claude Code shows ✘ Failed to connect, not Needs authentication — a bearer header suppresses the OAuth fallback entirely. If you see this, remove --header and re-add without it to let OAuth run. Also check claude mcp list for hidden whitespace warnings on pasted tokens.

Fix: Connection Timed Out at Startup

bash

MCP_TIMEOUT=60000 claude

powershell

$env:MCP_TIMEOUT = "60000"; claude

This is a different clock from a single tool call hanging mid-session — that's MCP_TOOL_TIMEOUT or a per-server timeout field (ms) in .mcp.json.

Fix: Server Response Gets Truncated

bash

export MAX_MCP_OUTPUT_TOKENS=50000

Claude Code warns above ~10,000 tokens of MCP output and truncates around 25,000 by default.

Fix: Server Connects but No Tools Appear

Run /mcp, select the server. Empty tool list usually means a missing required env var:

bash

claude mcp add my-server --env API_KEY=your_key -- npx -y @some/mcp-package

or in .mcp.json:

json

{
  "mcpServers": {
    "my-server": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@some/mcp-package"],
      "env": { "API_KEY": "your_key" }
    }
  }
}

Fix: PATH / Node.js / npx Issues

Claude Code spawns subprocesses in a different shell environment than your terminal, so node/npx can be "missing" even though your terminal finds them fine — especially with nvm.

Use the absolute path (which node) in your server's command field.
Make nvm load in non-interactive shells — add its init block to ~/.zshrc/~/.bashrc, not just ~/.zprofile.

Fix: Windows-Specific Failures

bash

claude mcp add --transport stdio my-server -- cmd /c npx -y @some/package

Without cmd /c, Windows can't execute npx directly (Connection closed). The --mcp-config flag has also been unreliable on Windows in some releases — use claude mcp add instead.

Fix: Changes to .mcp.json Don't Take Effect

Restart the session after editing. If servers still don't appear, check claude mcp list for parse warnings, and reset a stuck rejection with:

bash

claude mcp reset-project-choices

Fix: Server Name Conflicts with a Built-in Server

Claude Code reserves workspace, claude-in-chrome, and computer-use. A config using one of these is skipped silently. Pick a distinctive name, then confirm the winner with claude mcp list / claude mcp get <name> — this also resolves duplicate names across scopes, where local beats project beats user.

Fix: /mcp Shows "No MCP servers configured" but claude mcp list Disagrees

A known discrepancy on some versions: /mcp in-session says nothing's configured while claude mcp list shows servers connected (most common with project-scoped servers on Windows). If this happens:

Trust claude mcp list over /mcp.
Run /doctor for a fuller diagnostic.
Test whether the server actually works by asking Claude to use it by name.
If a project-scoped server never got an approval prompt at all, check .claude/settings.local.json for an enabledMcpServers entry, or run claude mcp reset-project-choices.

Fix: MCP Tools Don't Work in Non-Interactive / Scripted Mode

Servers connected via claude.ai-native connectors (not claude mcp add) have been reported unavailable under --print/--output-format stream-json, even when shown connected interactively. Prefer CLI-added servers for anything you script or run in CI.

Fix: A Local Server Corrupts Its Own Connection with Console Output

For stdio servers you maintain yourself: MCP uses stdout as the protocol channel. Any stray print() or verbose library logging to stdout corrupts the stream. Logs must go to stderr.

Test the Server Outside Claude Code Entirely

bash

npx @modelcontextprotocol/inspector --server-url https://mcp.example.com/mcp --transport http
npx @modelcontextprotocol/inspector --cli https://mcp.example.com/mcp --transport http --method tools/list

If the Inspector connects and lists tools, the fault is on the Claude Code side. If it fails too, the fault is the server, network, or credential.

Advanced Debugging: Run the Server Manually

Isolate whether the problem is Claude Code or the server by running the server's exact command or curling its URL directly, outside Claude Code.

Common Mistakes That Cause This

Running claude mcp add from the wrong project directory
Editing ~/.claude/settings.json instead of ~/.claude.json / .mcp.json
Omitting the -- separator before a local server's command
Assuming a server that works standalone will work identically under Claude Code, ignoring PATH differences
Not restarting the session after editing .mcp.json
On Windows, calling npx directly instead of cmd /c npx

FAQs

Why does claude mcp list show a server as connected but /mcp doesn't?

Run both from the same working directory. Local-scoped servers are tied to a specific project path, so checking from a different folder can show different results.

Does restarting Claude Code fix most MCP issues?

Only for one specific case: changes to .mcp.json are read at session start, so a restart is required after editing it. Restarting won't fix a PATH problem, a bad URL, or a missing environment variable.

Where does Claude Code actually store MCP server configuration?

Only ~/.claude.json (for local- and user-scoped servers) and <project>/.mcp.json (for project-scoped servers). No other file path is read for server definitions.

Why does my MCP server work when I run it manually but not through Claude Code?

This is almost always a PATH/environment mismatch — Claude Code spawns subprocesses in a different shell environment than your interactive terminal. Use absolute paths to nodes, or ensure your version manager (like nvm) initializes in non-interactive shells.

How do I remove an MCP server that's causing errors?

claude mcp remove <server-name>. If it's defined at more than one scope, add --scope local, --scope project, or --scope user to specify which copy to delete.

Can a project-scoped server run code on my machine without my consent?

No — the first time Claude Code encounters a project-scoped server (from a cloned repo's .mcp.json), it prompts for approval before running it.

Why does my server show connection but Claude never uses its tools?

Check /mcp and select the server to confirm its tool list isn't empty. An empty list means it needs a required environment variable, typically an API key, passed via --env or the env field in .mcp.json. If the tool list isn't empty and Claude simply isn't calling the tool, that's a separate issue — the model weighs your phrasing against its instructions, and a vague request can lose that judgment call even with a fully healthy server. Try invoking a specific MCP prompt directly with /mcp__servername__promptname (if the server exposes one) to remove the ambiguity and confirm the server itself works.

Does claude mcp add printing "Added" means the server is working?

No — it means the configuration was written to disk, not that a connection succeeded. Added and ✘ Failed to connect can both be true for the same server at the same time; they describe different steps. Always follow an ad with a claude mcp list to check the actual connection status.

Why does npx @playwright/mcp@latest fail with "Executable doesn't exist"?

The Playwright MCP server needs a Chromium binary that isn't bundled automatically. Run npx playwright install chromium once, then retry.

My MCP server worked yesterday and now every server in my config is gone — what happened?

This is the signature of a single malformed entry in .mcp.json or ~/.claude.json. A stray trailing comma, a smart quote pasted in from a web page instead of a straight quote, or a missing bracket can invalidate the whole file, not just one server's entry. Validate the file's JSON syntax (python3 -m json.tool path/to/.mcp.json will error out at the exact bad line) before assuming individual servers broke.

How do I test whether the problem is Claude Code or the MCP server itself?

Run the server standalone: for a local server, run its exact command/args directly in your terminal; for a hosted server, curl the URL or use the MCP Inspector (npx @modelcontextprotocol/inspector). If the server behaves correctly outside Claude Code, the fault is in your Claude Code configuration or environment, not the server.

Conclusion

Most "Claude Code MCP server not working" problems trace back to one of a small number of causes: the wrong config file, a project-scope mismatch, a PATH issue Claude Code hits but your terminal doesn't, a missing environment variable, or an unresolved authentication step. Start with claude mcp list and claude mcp get <name> to get the exact status and error detail, match it against the fixes above, and you'll usually isolate the cause in a couple of minutes rather than guessing through configuration changes.

(Word count: ~2,850 after incorporating additional verified failure modes — see note in Section 17. This runs above the original 2,000–2,500 target because the added sections cover genuinely distinct causes rather than padding; consider trimming the "stdout logging" and "non-interactive mode" subsections first if a hard length cap is required, since they serve a narrower slice of readers than the rest.)

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