unslothai/unsloth · warning · HTTPException

url is missing a host

Error message

url is missing a host

What it means

400 raised after scheme validation passes (http:// or https://) but urlparse finds no netloc — the authority/host component is empty. This catches malformed URLs where the host slot is blank, since a URL without a host cannot be dialed.

Source

Thrown at studio/backend/routes/mcp_servers.py:105

                "first token is an executable (not a URL).",
            )
        return trimmed
    parsed = urlparse(trimmed)
    if parsed.scheme not in ("http", "https"):
        if _looks_like_command(trimmed):
            detail = (
                "Local commands aren't enabled on this server. To allow them, "
                "set UNSLOTH_STUDIO_ALLOW_STDIO_MCP=1 and restart Unsloth, or use "
                "an http:// or https:// URL instead."
            )
        else:
            detail = (
                "MCP server address must start with http:// or https:// "
                "(for example https://example.com/mcp)."
            )
        raise HTTPException(status_code = 400, detail = detail)
    if not parsed.netloc:
        raise HTTPException(status_code = 400, detail = "url is missing a host")
    return trimmed


def _normalize_headers(headers: dict[str, str] | None) -> dict[str, str] | None:
    """Trim header names, drop empties, coerce values to str; None if empty."""
    if not headers:
        return None
    out: dict[str, str] = {}
    for raw_key, value in headers.items():
        key = str(raw_key).strip()
        if key:
            out[key] = str(value)
    return out or None


def _row_to_response(row: dict) -> McpServerResponse:
    return McpServerResponse(
        id = row["id"],

View on GitHub (pinned to 203007d190)

Solutions

1. Fix the URL to include a host: 'https://example.com/mcp', 'http://127.0.0.1:8080/mcp'.
2. When templating, assert the host variable is non-empty before building the URL.
3. Watch for doubled slashes after the scheme that push the host into the path.

Example fix

# before
url = f'http://{host}/mcp'   # host == '' -> 'http:///mcp' -> 400

# after
assert host, 'MCP host must be set'
url = f'http://{host}/mcp'

try { const u = new URL(url); if (!u.hostname) throw new Error('missing host'); } catch { throw new Error('invalid MCP url'); }

function urlHasHost(v) { try { return new URL(v).hostname.length > 0; } catch { return false; } }

When it happens

Trigger: POST/PUT with url values like 'http://', 'http:///path', 'https://:8080', or 'http:// /x' where everything lands in the path and the netloc stays empty.

Common situations: String-concatenation bugs building URLs from empty host variables (f'http://{host}/mcp' with host=''), or typos adding extra slashes after the scheme.

Related errors

• url must not be empty
• Enter an http(s):// URL, or a local command whose first toke
• MCP server address must start with http:// or https:// (for
• command must not be empty
• is_enabled must be true or false

AI-assisted analysis of unslothai/unsloth@203007d190 (2026-08-15). Data as JSON: /api/errors/9f190debeda692f4. Report an issue: GitHub.