What causes "MCP server "${name}": invalid URL "${server.url}"" in Mintplex-Labs/anything-llm?

Prefix the url with the scheme: http:// or https:// (e.g. http://localhost:8000, not localhost:8000).

Mintplex-Labs/anything-llm · error · Error

MCP server "${name}": invalid URL "${server.url}"

Error message

MCP server "${name}": invalid URL "${server.url}"

What it means

Thrown by #validateServerDefinitionByType when server.url is present but `new URL(server.url)` throws — i.e. the value is not a parseable absolute URL. The caught exception is swallowed and replaced with a message naming the server and echoing the offending string. This runs only for http-classified servers and after the missing-url check.

Source

Thrown at server/utils/MCP/hypervisor/index.js:384

      // "type" is optional for http servers - when omitted, SSE is assumed
      // (see createHttpTransport). An explicit unknown value is a config error.
      if (
        server.type !== undefined &&
        !["sse", "streamable", "http"].includes(server.type)
      ) {
        throw new Error("MCP server type must have sse or streamable value.");
      }

      if (!server.url) {
        throw new Error(
          `MCP server "${name}": missing required "url" for ${server.type || "sse"} transport`
        );
      }

      try {
        new URL(server.url);
      } catch {
        throw new Error(`MCP server "${name}": invalid URL "${server.url}"`);
      }
      return;
    }

    if (type === "stdio") {
      if (
        Object.prototype.hasOwnProperty.call(server, "args") &&
        !Array.isArray(server.args)
      )
        throw new Error("MCP server args must be an array");
    }
    return;
  }

  /**
   * Setup the server transport by type and server definition
   * @param {Object} server - The server definition
   * @param {MCPServerTypes} type - The server type

View on GitHub (pinned to 526360e320)

Solutions

Prefix the url with the scheme: http:// or https:// (e.g. http://localhost:8000, not localhost:8000).
Trim whitespace around the url value.
Ensure the url is absolute (includes host), not a relative path.
The message echoes the bad value — compare it against a known-good URL.

Example fix

// before
{
  "myServer": { "url": "localhost:8000/mcp" }
}

// after
{
  "myServer": { "url": "http://localhost:8000/mcp" }
}

Defensive patterns

Strategy: validation

Validate before calling

function isValidUrlString(u) {
  try { new URL(u); return true; } catch { return false; }
}
// before starting:
if (!isValidUrlString(server.url)) {
  throw new Error(`MCP server '${name}' has an invalid url '${server.url}'. Include the scheme (http:// or https://).`);
}

Type guard

/** @param {unknown} u */
function isAbsoluteUrl(u) {
  if (typeof u !== 'string') return false;
  try { const p = new URL(u); return p.protocol === 'http:' || p.protocol === 'https:'; } catch { return false; }
}

Try / catch

try {
  new URL(server.url);
} catch {
  throw new Error(`MCP server '${name}' url '${server.url}' is not a valid absolute URL — add http:// or https://`);
}

Prevention

Always include the scheme (http:// or https://) — 'localhost:8000' alone is invalid.
Trim whitespace around url values copied from elsewhere.
Validate with new URL() in your config loader before the hypervisor sees it.
Use absolute URLs only, never relative paths.

When it happens

Trigger: A server url that is a relative path (e.g. /mcp), missing the scheme (e.g. localhost:8000 instead of http://localhost:8000), contains illegal characters, has whitespace, or is otherwise malformed so the WHATWG URL parser rejects it.

Common situations: Omitting the http:// or https:// scheme (the most common cause — 'localhost:8000' is not a valid absolute URL); trailing/leading spaces from copy-paste; using a protocol the parser rejects; relative paths meant for a stdio server mistakenly placed under url.

Related errors

AI-assisted analysis of Mintplex-Labs/anything-llm@526360e320 (2026-08-13). Data as JSON: /api/errors/8fb31d9f860dd46e. Report an issue: GitHub.