declare const Base64Prefix: "data:application/json;base64";
type Base64String = `${typeof Base64Prefix},${string}`;
/**
 * Checks if a given string is a base64 encoded JSON string.
 * @param input - The string to be checked.
 * @returns True if the input string starts with "data:application/json;base64", false otherwise.
 * @example
 * ```ts
 * isBase64JSON("data:application/json;base64,eyJ0ZXN0IjoiYmFzZTY0In0=")
 * // true
 * ```
 */
export declare function isBase64JSON(input: string): input is Base64String;
/**
 * Parses a base64 string and returns the decoded string.
 * @param input - The base64 string to parse.
 * @returns The decoded string.
 * @example
 * ```ts
 * parseBase64String("data:application/json;base64,eyJ0ZXN0IjoiYmFzZTY0In0=")
 * // '{"test":"base64"}'
 * ```
 */
export declare function parseBase64String(input: Base64String): string;
export {};
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