MCP Config JSON Invalid / Not Loading

Why JSON errors are silent

Claude Desktop parses claude_desktop_config.json at startup as a single JSON document. If parsing fails, the entire file is rejected — Claude Desktop cannot fall back to individual servers because it never got past reading the file. All servers are disabled and no error appears in the Claude UI. The only indicator is the missing tools icon.

How to validate your config

# macOS / Linux
cat ~/Library/Application\ Support/Claude/claude_desktop_config.json | python3 -m json.tool

# Windows (PowerShell)
Get-Content "$env:APPDATA\Claude\claude_desktop_config.json" | ConvertFrom-Json

# Any platform - using node
node -e "JSON.parse(require('fs').readFileSync(process.argv[1],'utf8'))" ~/Library/Application\ Support/Claude/claude_desktop_config.json

If the command throws an error, you will see the line number and character position of the problem. Fix it, then rerun the command to confirm the file is now valid before restarting Claude Desktop.

Common JSON errors and fixes

1. Trailing comma (most common)

JSON does not allow a comma after the last item in an object or array. This is valid JavaScript but not valid JSON.

// WRONG - trailing comma after the last server
{
  "mcpServers": {
    "filesystem": {
      "command": "/usr/local/bin/npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/tmp"],    ← remove this
    },    ← and this
  }
}

// CORRECT
{
  "mcpServers": {
    "filesystem": {
      "command": "/usr/local/bin/npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/tmp"]
    }
  }
}

2. Unescaped backslash in Windows path

In JSON strings, a backslash must be doubled. A single backslash is an escape character and will cause a parse error unless followed by a valid escape sequence (\n, \t, \\, \", etc.).

// WRONG - single backslashes
"command": "C:\Users\you\AppData\Roaming\npm\npx.cmd"

// CORRECT option 1 - forward slashes (recommended)
"command": "C:/Users/you/AppData/Roaming/npm/npx.cmd"

// CORRECT option 2 - escaped backslashes
"command": "C:\\Users\\you\\AppData\\Roaming\\npm\\npx.cmd"

3. Comments in JSON

JSON does not support comments. The // syntax is JavaScript, not JSON.

// WRONG - JSON does not allow comments
{
  "mcpServers": {
    // "old-server": { ... },    ← will cause parse error
    "filesystem": { ... }
  }
}

To "comment out" a server, delete the entry entirely or rename the key to something like "_disabled_filesystem".

4. Single quotes instead of double quotes

// WRONG - single quotes
{
  'mcpServers': {
    'filesystem': {
      'command': '/usr/local/bin/npx'
    }
  }
}

// CORRECT - always double quotes
{
  "mcpServers": {
    "filesystem": {
      "command": "/usr/local/bin/npx"
    }
  }
}

5. Missing closing brace or bracket

When you add a new server, it is easy to forget to close all braces. Each { needs a matching } and each [ needs a matching ]. Use an editor with bracket matching (VS Code highlights unmatched braces in red) or a JSON validator.

// WRONG - missing closing brace for github server
{
  "mcpServers": {
    "filesystem": {
      "command": "/usr/local/bin/npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/tmp"]
    },
    "github": {
      "command": "/usr/local/bin/npx",
      "args": ["-y", "@modelcontextprotocol/server-github"]
              ← missing closing } for github, } for mcpServers, } for root
}

Correct config structure

For reference, this is the minimal valid config structure:

{
  "mcpServers": {
    "server-name": {
      "command": "/absolute/path/to/npx",
      "args": ["-y", "package-name"]
    }
  }
}

With multiple servers and env vars:

{
  "mcpServers": {
    "filesystem": {
      "command": "/usr/local/bin/npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/Users/you/projects"]
    },
    "github": {
      "command": "/usr/local/bin/npx",
      "args": ["-y", "@modelcontextprotocol/server-github"],
      "env": {
        "GITHUB_PERSONAL_ACCESS_TOKEN": "ghp_yourtoken"
      }
    }
  }
}

Config at wrong file path

If the JSON is valid but servers still do not appear, confirm you are editing the right file:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json (typically C:\Users\NAME\AppData\Roaming\Claude\claude_desktop_config.json)
• Linux: ~/.config/Claude/claude_desktop_config.json

Open the file directly to confirm you are editing the right one:

# macOS
open ~/Library/Application\ Support/Claude/claude_desktop_config.json

# Windows
notepad "$env:APPDATA\Claude\claude_desktop_config.json"

# Linux
nano ~/.config/Claude/claude_desktop_config.json

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