diff --git a/src/application/dto/auth.ts b/src/application/dto/auth.ts
new file mode 100644
index 0000000..ebeb605
--- /dev/null
+++ b/src/application/dto/auth.ts
@@ -0,0 +1,46 @@
+/**
+ * Input for the login endpoint.
+ * The caller provides the admin API token to obtain a session cookie.
+ */
+export interface LoginInput {
+  /** Admin API token for authentication */
+  token: string;
+}
+
+/**
+ * Active authentication session information.
+ */
+export interface AuthSession {
+  /** Authenticated username (currently always "admin") */
+  username: string;
+  /** Session expiry timestamp; null for bearer-token sessions */
+  expiresAt: Date | null;
+  /** Authentication method used */
+  method: 'cookie' | 'bearer';
+}
+
+/**
+ * Response payload for a successful login.
+ */
+export interface LoginResponse {
+  /** Authenticated username */
+  username: string;
+}
+
+/**
+ * Response payload for logout.
+ */
+export interface LogoutResponse {
+  /** Whether the logout succeeded */
+  success: boolean;
+}
+
+/**
+ * Response payload for the current-user (/me) endpoint.
+ */
+export interface UserInfoResponse {
+  /** Authenticated username */
+  username: string;
+  /** ISO-8601 session expiry timestamp; null when using bearer token */
+  expiresAt: string | null;
+}
diff --git a/src/application/dto/bucket.ts b/src/application/dto/bucket.ts
new file mode 100644
index 0000000..e6f2736
--- /dev/null
+++ b/src/application/dto/bucket.ts
@@ -0,0 +1,47 @@
+/**
+ * Input for creating a new bucket.
+ */
+export interface CreateBucketInput {
+  /** Bucket name (must match S3 naming rules: 3-63 chars, lowercase, no underscore) */
+  name: string;
+}
+
+/**
+ * Single bucket representation returned by bucket endpoints.
+ */
+export interface BucketResponse {
+  /** Bucket UUID */
+  id: string;
+  /** Bucket name */
+  name: string;
+  /** ISO-8601 timestamp of when the bucket was created */
+  createdAt: string;
+  /** Number of non-deleted objects in the bucket */
+  objectCount?: number;
+}
+
+/**
+ * Response payload for the list-buckets endpoint.
+ */
+export interface BucketListResponse {
+  /** Array of buckets */
+  buckets: BucketResponse[];
+}
+
+/**
+ * Response payload for bucket creation.
+ */
+export interface CreateBucketResponse {
+  /** Bucket UUID */
+  id: string;
+  /** Bucket name */
+  name: string;
+}
+
+/**
+ * Response payload for bucket deletion.
+ */
+export interface DeleteBucketResponse {
+  /** Whether the deletion succeeded */
+  success: boolean;
+}
diff --git a/src/application/dto/file.ts b/src/application/dto/file.ts
new file mode 100644
index 0000000..7bb9d2a
--- /dev/null
+++ b/src/application/dto/file.ts
@@ -0,0 +1,68 @@
+/**
+ * Public file information response returned by the file-info endpoint.
+ * Mirrors the JSON shape of GET /file/:publicId/info.
+ */
+export interface FileInfoResponse {
+  /** Public, shareable identifier (nanoid) */
+  public_id: string;
+  /** Stored file name */
+  file_name: string;
+  /** MIME type of the stored file */
+  mime_type: string;
+  /** File size in bytes */
+  size_bytes: number;
+  /** High-level file category (e.g. "document", "photo") */
+  file_type: string;
+  /** ISO-8601 timestamp of when the file record was created */
+  created_at: string;
+}
+
+/**
+ * Summary-level file metadata used internally for constructing
+ * upload responses and object listing entries.
+ */
+export interface FileMetadata {
+  /** Public, shareable identifier (nanoid) */
+  publicId: string;
+  /** Telegram file identifier used to retrieve the file from Telegram CDN */
+  telegramFileId: string;
+  /** Telegram unique file identifier (persists across re‑uploads) */
+  telegramFileUniqueId: string;
+  /** Chat ID where the file or archive was stored */
+  storageChatId: number;
+  /** Message ID of the stored file or archive */
+  storageMessageId: number;
+  /** Stored file name */
+  fileName: string;
+  /** MIME type of the stored file */
+  mimeType: string;
+  /** File size in bytes */
+  sizeBytes: number;
+  /** High-level file category */
+  fileType: string;
+  /** Telegram user ID of the uploader; 0 when unknown or system */
+  uploaderId: number;
+  /** Timestamp of file record creation */
+  createdAt: Date | string | number;
+}
+
+/**
+ * Upload response shape returned to API callers.
+ * Mirrors the JSON output of the /api/upload endpoint.
+ */
+export interface UploadResponse {
+  /** Public, shareable identifier */
+  public_id: string;
+  /** Stored file name */
+  file_name: string;
+  /** MIME type */
+  mime_type: string;
+  /** File size in bytes */
+  size_bytes: number;
+  /** High-level file category */
+  file_type: string;
+  /** ISO-8601 creation timestamp */
+  created_at: string;
+  /** Public download URL */
+  download_url: string;
+}
diff --git a/src/application/dto/s3.ts b/src/application/dto/s3.ts
new file mode 100644
index 0000000..61d72a7
--- /dev/null
+++ b/src/application/dto/s3.ts
@@ -0,0 +1,87 @@
+/**
+ * A single S3 object as it appears in listing results.
+ */
+export interface S3ObjectResponse {
+  /** The object key (full path within the bucket) */
+  key: string;
+  /** Stored file name (basename of the key) */
+  fileName: string;
+  /** MIME type of the stored object */
+  mimeType: string;
+  /** Object size in bytes */
+  sizeBytes: number;
+  /** High-level file category */
+  fileType: string;
+  /** SHA-256 hex digest of the object content */
+  etag: string | null;
+  /** ISO-8601 timestamp of last modification */
+  lastModified: string;
+  /** Public download URL */
+  downloadUrl: string;
+}
+
+/**
+ * Response payload for S3 ListObjectsV1 / ListObjectsV2.
+ */
+export interface S3ListObjectsResponse {
+  /** Array of object summaries */
+  objects: S3ObjectResponse[];
+  /** Common prefixes when a delimiter was used (e.g. "folder/" entries) */
+  prefixes: string[];
+  /** Whether more results are available */
+  isTruncated: boolean;
+  /** Token to pass as continuation-token to retrieve the next page */
+  nextContinuationToken: string | null;
+}
+
+/**
+ * Input for the copy-object operation (Web API v1).
+ */
+export interface S3CopyObjectInput {
+  /** Source object key within the same or source bucket */
+  sourceKey: string;
+  /** Destination bucket name; defaults to the source bucket when omitted */
+  destBucket?: string;
+  /** Destination object key */
+  destKey: string;
+}
+
+/**
+ * Response payload for the copy-object operation.
+ */
+export interface S3CopyObjectResponse {
+  /** Source object key that was copied */
+  sourceKey: string;
+  /** Destination object key */
+  destKey: string;
+  /** Destination bucket name */
+  destBucket: string;
+}
+
+/**
+ * Summary of a multipart upload in listing results.
+ */
+export interface S3MultipartUploadResponse {
+  /** The object key being uploaded */
+  key: string;
+  /** Upload identifier (nanoid) */
+  uploadId: string;
+  /** ISO-8601 timestamp when the upload was initiated */
+  initiatedAt: Date;
+  /** Identifier string of the upload initiator */
+  initiatedBy: string;
+}
+
+/**
+ * Summary of a single part within a multipart upload.
+ */
+export interface S3MultipartPartResponse {
+  /** 1-indexed part number */
+  partNumber: number;
+  /** ETag of the part content */
+  etag: string;
+  /** Part size in bytes */
+  sizeBytes: number;
+  /** ISO-8601 timestamp when the part was stored */
+  createdAt: Date;
+}
diff --git a/src/application/dto/upload.ts b/src/application/dto/upload.ts
new file mode 100644
index 0000000..454568c
--- /dev/null
+++ b/src/application/dto/upload.ts
@@ -0,0 +1,46 @@
+/**
+ * Input for the upload file use case.
+ * Carries all metadata needed to persist an uploaded file,
+ * including its temporary location on disk and optional bucket/S3 context.
+ */
+export interface UploadInput {
+  /** Absolute path to the temporary file on disk */
+  tempPath: string;
+  /** SHA-256 hex digest of the file content */
+  fileHash: string;
+  /** Original file name (may include extension) */
+  fileName: string;
+  /** MIME type detected from content inspection or request header */
+  mimeType: string;
+  /** High-level file category (e.g. "document", "photo", "video") */
+  fileType: string;
+  /** File size in bytes */
+  sizeBytes: number;
+  /** Telegram user ID of the uploader; 0 when unknown or system */
+  uploaderId?: number;
+  /** Target bucket UUID for S3-compatible storage; null when un-bucketed */
+  bucketId?: string | null;
+  /** Object key within the bucket for S3-compatible storage; null when un-bucketed */
+  s3Key?: string | null;
+}
+
+/**
+ * Output from the upload file use case.
+ * Contains the public-facing file metadata returned to the caller.
+ */
+export interface UploadOutput {
+  /** Public, shareable identifier (nanoid) */
+  publicId: string;
+  /** Stored file name (may have been normalized with extension) */
+  fileName: string;
+  /** MIME type of the stored file */
+  mimeType: string;
+  /** File size in bytes */
+  sizeBytes: number;
+  /** High-level file category */
+  fileType: string;
+  /** ISO-8601 timestamp of when the file record was created */
+  createdAt: Date;
+  /** Public download URL */
+  downloadUrl: string;
+}