continuedev/continue · error · Error

Invalid URL-based MCP tool reference "${toolRef}": the part

Error message

Invalid URL-based MCP tool reference "${toolRef}": the part after the last colon must be either a port number or a valid tool name (alphanumeric, underscores, hyphens).

What it means

For a URL-based tool reference with a colon after the protocol, the segment after the last colon must be a port number or match /^[a-zA-Z0-9_-]+$/ (tool name). Anything else triggers this error.

Source

Thrown at packages/config-yaml/src/markdown/agentFiles.ts:157

          afterLastColon === "" ||
          /^[a-zA-Z0-9_-]+$/.test(afterLastColon)
        ) {
          // It's a tool name (or empty string)
          // Reject references with whitespace to prevent silent misconfigurations
          if (/\s/.test(toolRef)) {
            throw new Error(
              `Invalid MCP tool reference "${toolRef}": colon-separated tool references cannot contain whitespace. ` +
                `Use format "https://server:tool_name" without spaces.`,
            );
          }

          const mcpServer = toolRef.substring(0, lastColonIndex);
          const toolName = afterLastColon;

          tools.push({ mcpServer, toolName });
          mcpServerSet.add(mcpServer);
        } else {
          throw new Error(
            `Invalid URL-based MCP tool reference "${toolRef}": the part after the last colon must be either a port number or a valid tool name (alphanumeric, underscores, hyphens).`,
          );
        }
      } else {
        // No colon after the protocol, treat the whole thing as the server
        const mcpServer = toolRef;
        tools.push({ mcpServer });
        mcpServerSet.add(mcpServer);
      }
    } else if (toolRef.includes("/")) {
      // MCP tool reference: "owner/package" or "owner/package:tool_name"
      const colonIndex = toolRef.indexOf(":");

      if (colonIndex > 0) {
        // Specific tool: "owner/package:tool_name"
        // Reject references with whitespace to prevent silent misconfigurations
        if (/\s/.test(toolRef)) {
          throw new Error(

View on GitHub (pinned to 5522c6f44c)

Solutions

  1. Use only alphanumeric, underscore, and hyphen in the tool name after the colon
  2. Move path-like structure into the server part or drop it
  3. Verify against the actual MCP server's published tool names

Example fix

# before
tools:
  - "https://server:cat/tool"
# after
tools:
  - "https://server:tool"
Defensive patterns

Strategy: validation

Validate before calling

const ok = toolRefs.every(r => {
  const after = r.substring(r.lastIndexOf(':') + 1);
  return /^\d+$/.test(after) || /^[a-zA-Z0-9_-]+$/.test(after);
});

Type guard

function isValidUrlToolRef(ref: string): boolean {
  const after = ref.substring(ref.lastIndexOf(':') + 1);
  return /^\d+$/.test(after) || /^[a-zA-Z0-9_-]+$/.test(after);
}

Try / catch

try { parseAgentFileTools(refs); } catch (e) { if (e.message.includes('port number or a valid tool name')) { /* fix the tool name */ } }

Prevention

When it happens

Trigger: A tools entry like 'https://server:tool.name!' or 'https://server:tool name' — post-colon segment containing dots, slashes, or other non-[a-zA-Z0-9_-] characters when not a port.

Common situations: Passing full tool paths ('server:category/tool'), tool names with special characters, or malformed URLs.

Related errors

AI-assisted analysis of continuedev/continue@5522c6f44c (2026-08-27). Data as JSON: /api/errors/8b55613e7f950ba4. Report an issue: GitHub.