MCP server config generator and validator
Most MCP servers that "do not show up" are a config problem, not a server problem. The key is nested wrong, the wrong file was edited, or a Windows path broke the JSON. Build a config for your client, or paste the one that is failing and find the line.
Generated config
Check a config that is failing
Paste a config and press Check it.
What usually breaks
Four mistakes account for most of it. The servers sit under the wrong top-level key, because each client names it differently: Claude Desktop, Claude Code and Cursor use mcpServers, VS Code uses servers, Zed uses context_servers, and Codex uses TOML rather than JSON at all. The wrong file is edited, which on Windows is worse than it sounds, since an MSIX install redirects writes to a virtualised path and your edit lands in a file the app never reads.
A Windows path breaks the JSON, because C:\Users is not a valid escape sequence, so the whole file fails to parse and every server disappears at once. And environment values are not strings, so a token pasted without quotes is rejected. All four are caught below.
Client schemas move. Check your client's own documentation before trusting an example, and keep the file you generated under version control so an editor can diff the next change.
If you are new to the protocol itself rather than to the config, the MCP explainer covers what a server exposes and how a client discovers it, which makes the shape of the object below easier to read.