type FetchImpl = (input: string, init?: RequestInit) => Promise<Response>;
export interface NormalizeOptions {
    /** Override the underlying fetch. Defaults to `globalThis.fetch`. */
    fetchImpl?: FetchImpl;
    /** Probe timeout per scheme attempt. Default 10s. */
    timeoutMs?: number;
}
export interface NormalizeResult {
    /** Final URL string with explicit http(s) scheme. */
    url: string;
    /** True when a scheme had to be added (caller may want to echo a notice). */
    rewrote: boolean;
}
export declare class UnreachableUrlError extends Error {
    readonly input: string;
    constructor(input: string);
}
/**
 * Resolve a user-supplied URL to one with an explicit http(s) scheme.
 *
 * Behaviour:
 *  1. If the input already parses as an http(s) URL, return it unchanged.
 *  2. Otherwise probe `https://<input>`. Any HTTP response (incl. 4xx/5xx)
 *     counts as "reachable" — only connection errors fall through.
 *  3. If https fails, probe `http://<input>`.
 *  4. If both fail, throw `UnreachableUrlError`.
 */
export declare function normalizeUrl(input: string, opts?: NormalizeOptions): Promise<NormalizeResult>;
export {};