How do I validate an MCP config JSON file?

Paste the file into the validator above. It first checks that the JSON is valid and shows the line and column of any syntax error. Then it checks the server settings: command or url, args, env, headers and type. Results appear as you type.

What is the difference between mcpServers and servers?

As far as I know, Claude Desktop, Cursor, Claude Code, Windsurf and Cline use a top-level mcpServers key, while VS Code’s mcp.json uses servers. Check your client’s documentation, because each client defines its own format.

Where is the MCP config file located?

It depends on the client. Claude Desktop uses claude_desktop_config.json, Cursor uses .cursor/mcp.json, Claude Code uses .mcp.json in a project, and VS Code uses .vscode/mcp.json. Check your client’s documentation for the exact path on your system.

Why does my MCP server fail to start?

Common causes are invalid JSON, a full command line placed in the command field, missing -y when using npx, a program that is not on the PATH of the app, and env values that are not strings. This validator flags all of these except a missing PATH program.

Can an MCP config have comments or trailing commas?

No. The file must be strict JSON, so comments, trailing commas and single quotes cause errors. Remove them, or use the Format JSON button on a valid file to tidy it.

Is it safe to paste my MCP config here?

The check runs in your browser and nothing is uploaded. Still, remove API keys and tokens first. The Share link button puts your text in the URL, so never share a link that contains secrets.

MCP Config JSON Validator: Check Server Settings

MCP config JSON validator

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Free online MCP config checker. Paste your claude_desktop_config.json, .cursor/mcp.json or .mcp.json and see JSON errors and server problems with line numbers. Everything runs in your browser. Nothing is uploaded.

Inputs

Paste your MCP config

Output

Results

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robots.txt AI Bot Generator →	Generate rules to block, allow, or limit AI crawlers like GPTBot, ClaudeBot, and CCBot.
llms.txt Generator →	Build clean, structured Markdown maps to help LLMs understand your website content.
llms.txt Validator →	Lint and validate llms.txt syntax, check broken links, and verify standard formatting.
agents.md Builder →	Create configuration files for AI coding agents with tools, rules, and system behavior.

What does an MCP config validator check?

MCP (Model Context Protocol) clients read a JSON file that lists the servers they should start or connect to. A small mistake, such as a trailing comma, a number in env, or a full command line in command, usually makes a server silently fail. This validator catches those mistakes with line numbers before you restart your client. Clients differ in details, so treat the results as guidance and check your client’s documentation.

MCP config reference: 60 rules and settings

Severity is a recommended level. The validator above checks JSON syntax and server settings. Location and client rows are reference only, and rows marked Unverified are items I could not confirm, so check your client’s documentation.

Showing 60 of 60 rules & specifications

Rule / Setting / Query	Specification & Fix	Severity Level	Scope / Category
What is an MCP config file?	A JSON file that an MCP client reads to learn which servers to start or connect to. Each client defines its own file name and location.	Reference	File & Location
Claude Desktop config file	`claude_desktop_config.json`. On macOS it sits in `~/Library/Application Support/Claude/`, and on Windows in `%APPDATA%\Claude\`.	Reference	File & Location
Cursor MCP config location	`.cursor/mcp.json` inside a project, or `~/.cursor/mcp.json` for all projects.	Reference	File & Location
Claude Code MCP config	A `.mcp.json` file in the project root holds shared servers. You can also add servers with the `claude mcp add` command.	Reference	File & Location
VS Code MCP config	`.vscode/mcp.json`, with a top-level `servers` key instead of `mcpServers`.	Reference	File & Location
Windsurf MCP config location	As far as I know it is `~/.codeium/windsurf/mcp_config.json`. Check Windsurf’s documentation for the current path.	Unverified	File & Location
Cline MCP settings file	Cline keeps servers in `cline_mcp_settings.json`, which you open from its MCP Servers panel. Check Cline’s documentation to confirm.	Unverified	File & Location
mcpServers vs servers key	Most clients use `mcpServers`. VS Code uses `servers`. This validator accepts either and warns if both exist.	Reference	File & Location
Top-level value must be an object	The file must start with `{`. An array or a string at the top level is invalid.	Fatal Error	File & Location
Trailing comma error	A comma after the last item, such as `"a": 1,}`, is invalid. Fix: remove the last comma.	Fatal Error	JSON Syntax
Comments in JSON	`//` and `/* */` comments are not allowed. Fix: delete them, or keep notes in a separate file.	Fatal Error	JSON Syntax
Single quotes error	Use double quotes: `"command"`, not `'command'`.	Fatal Error	JSON Syntax
Curly quotes from copy-paste	Quotes copied from a web page or a document can be curly (“ ”). Fix: replace them with straight `"` quotes.	Fatal Error	JSON Syntax
Missing comma between servers	Every server entry except the last needs a comma after its closing brace. The error line is usually the one after the missing comma.	Fatal Error	JSON Syntax
Unclosed bracket or brace	Each `{` needs a `}` and each `[` needs a `]`. Format the file in an editor to find the mismatch.	Fatal Error	JSON Syntax
Windows path backslashes	Write `"C:\\Users\\me"` with doubled backslashes, or use forward slashes: `"C:/Users/me"`.	Fatal Error	JSON Syntax
Duplicate server names	If two servers share a name, JSON keeps only the last one. Fix: give each server a unique name.	Fatal Error	JSON Syntax
BOM at the start of the file	A byte order mark can break strict parsers. Fix: save as UTF-8 without BOM.	Warning	JSON Syntax
Unquoted keys	Keys must be in double quotes. `{command: "npx"}` is JavaScript, not JSON.	Fatal Error	JSON Syntax
The command field	The program to run for a local server, for example `"command": "npx"`.	Fatal Error	Local Servers
The args field	An array of strings, one item per argument: `"args": ["-y", "package-name"]`.	Fatal Error	Local Servers
Full command line in command	`"command": "npx -y pkg"` is wrong. Fix: `"command": "npx", "args": ["-y", "pkg"]`.	Warning	Local Servers
Flag and value in one arg	`"--port 3000"` is one argument. Fix: `"--port", "3000"` as two items.	Warning	Local Servers
Numbers in args	Every item in `args` must be a string. Write `"3000"`, not `3000`.	Fatal Error	Local Servers
npx needs -y	Add `"-y"` to args so npx does not stop to ask before installing a package. This validator shows it as a tip.	Best Practice	Local Servers
Python servers with uvx	Many Python servers run with `"command": "uvx"` and the package name in `args`, for example `["mcp-server-git"]`.	Reference	Local Servers
Docker-based servers	Use `"command": "docker"` with `"args": ["run", "-i", "--rm", "image-name"]`. The `-i` keeps stdin open for the server.	Reference	Local Servers
Node scripts with absolute path	For your own server, use an absolute path: `"args": ["/full/path/to/server.js"]`. Relative paths depend on the client’s working directory.	Best Practice	Local Servers
Program not found (PATH)	Apps started from a menu or dock may not inherit your shell PATH, so tools from nvm or pyenv are missed. Fix: use the full path to the executable.	Warning	Local Servers
The cwd field	Some clients support `"cwd"` to set the working directory. Check your client’s documentation before relying on it.	Unverified	Local Servers
Logs on stdout break stdio servers	A stdio server must write only protocol messages to stdout. Send logs to stderr.	Warning	Local Servers
The url field	Remote servers use `"url": "https://example.com/mcp"`. It must be an absolute URL.	Fatal Error	Remote Servers
The type field	Most clients accept `"type": "stdio"`, `"http"` or `"sse"`. This validator warns about other values.	Warning	Remote Servers
type stdio with a url	`"type": "stdio"` needs `command`. Fix: remove the type or switch to `http` or `sse`.	Fatal Error	Remote Servers
type http or sse with a command	`"type": "http"` or `"sse"` needs `url`. Fix: add a url or set the type to `stdio`.	Fatal Error	Remote Servers
Both command and url	Use `command` for a local server or `url` for a remote one, not both.	Fatal Error	Remote Servers
Streamable HTTP vs SSE	Newer MCP specification revisions replace the older HTTP+SSE transport with Streamable HTTP. Check which one your server and client support.	Reference	Remote Servers
http instead of https	Use `https://` for remote servers. This validator allows `http://` only for `localhost`.	Warning	Remote Servers
The headers field	An object of string values, for example `"headers": {"Authorization": "Bearer ..."}`.	Fatal Error	Remote Servers
The serverUrl key	Some clients use `serverUrl` instead of `url`. This validator accepts it and shows a tip.	Reference	Remote Servers
OAuth sign-in for remote servers	Some clients handle OAuth in their own interface instead of in the JSON file. Check your client’s documentation.	Unverified	Remote Servers
Local HTTP servers	`http://localhost:3000/mcp` is fine for development. The https warning does not apply to `localhost`.	Reference	Remote Servers
The env field	An object of string values: `"env": {"API_KEY": "value"}`.	Fatal Error	Secrets & Security
Booleans and numbers in env	`"DEBUG": true` is invalid for env. Fix: `"DEBUG": "true"`.	Fatal Error	Secrets & Security
Hard-coded secrets	Tokens and API keys written in the file can leak. This validator warns about secret-looking values in env and headers.	Warning	Secrets & Security
Committing .mcp.json to Git	Project config files are often committed. Keep secrets out of them, or add the file to `.gitignore`.	Warning	Secrets & Security
Environment variable expansion	Some clients can read values from environment variables, with different syntax. Check your client’s documentation before using `${VAR}`.	Unverified	Secrets & Security
VS Code inputs for secrets	VS Code’s `mcp.json` supports an `inputs` section that prompts for a secret instead of storing it in the file.	Reference	Secrets & Security
Limit filesystem server paths	Give a filesystem server only the folders it needs. Avoid `/` or your whole home folder.	Best Practice	Secrets & Security
Only install trusted servers	A local MCP server runs code with your user permissions. Install servers only from sources you trust.	Best Practice	Secrets & Security
Changes not picked up	Many clients read the file only at startup. Fully quit and reopen the client after editing it.	Warning	Troubleshooting
Where to find Claude Desktop logs	Claude Desktop writes MCP logs to a Logs folder, for example `~/Library/Logs/Claude` on macOS. Check its documentation for your system.	Unverified	Troubleshooting
Test a server with MCP Inspector	Run `npx @modelcontextprotocol/inspector` to try a server outside any client and see its tools.	Reference	Troubleshooting
Server name rules	Use short names with letters, numbers, `-` and `_`. This validator shows a tip for spaces or special characters.	Best Practice	Troubleshooting
Too many servers or tools	Many servers add many tools and slow startup. Enable only what you need.	Best Practice	Troubleshooting
Disabling a server	Some clients support `"disabled": true`. Others need you to delete the entry. Check your client’s documentation.	Unverified	Troubleshooting
Global vs project config	A global file applies to every project. A project file applies only there. Put personal servers in the global file.	Reference	Troubleshooting
Pin package versions	Use `package@1.2.3` in args so an update does not change behavior unexpectedly.	Best Practice	Troubleshooting
Validate the config in CI	Run `node -e "JSON.parse(require('fs').readFileSync('.mcp.json','utf8'))"` in a check to catch syntax errors before merging.	Best Practice	Troubleshooting
Share a config safely	Remove API keys and tokens first. The Share link button puts your text in the URL.	Best Practice	Troubleshooting

FAQ

Question	Answer
How do I validate an MCP config JSON file?	Paste the file into the validator above. It first checks that the JSON is valid and shows the line and column of any syntax error. Then it checks the server settings: command or url, args, env, headers and type. Results appear as you type.
What is the difference between mcpServers and servers?	As far as I know, Claude Desktop, Cursor, Claude Code, Windsurf and Cline use a top-level mcpServers key, while VS Code’s mcp.json uses servers. Check your client’s documentation, because each client defines its own format.
Where is the MCP config file located?	It depends on the client. Claude Desktop uses claude_desktop_config.json, Cursor uses .cursor/mcp.json, Claude Code uses .mcp.json in a project, and VS Code uses .vscode/mcp.json. Check your client’s documentation for the exact path on your system.
Why does my MCP server fail to start?	Common causes are invalid JSON, a full command line placed in the command field, missing -y when using npx, a program that is not on the PATH of the app, and env values that are not strings. This validator flags all of these except a missing PATH program.
Can an MCP config have comments or trailing commas?	No. The file must be strict JSON, so comments, trailing commas and single quotes cause errors. Remove them, or use the Format JSON button on a valid file to tidy it.
Is it safe to paste my MCP config here?	The check runs in your browser and nothing is uploaded. Still, remove API keys and tokens first. The Share link button puts your text in the URL, so never share a link that contains secrets.