diff --git a/internal/db/db.go b/internal/db/db.go
index 374732b..6296f0d 100644
--- a/internal/db/db.go
+++ b/internal/db/db.go
@@ -7,9 +7,18 @@ import (
 )
 
 type DB interface {
+	// Return nil if share does not exist
 	GetShare(ctx context.Context, slug string) (*types.Share, error)
+
+	// Returns error if share already exists
 	CreateShare(ctx context.Context, share *types.Share) error
+
+	// Returns error if share does not exist
 	DeleteShare(ctx context.Context, slug string) error
+
+	// Returns all shares
 	GetAllShares(ctx context.Context) ([]*types.Share, error)
+
+	// Close the database
 	Close() error
 }
diff --git a/internal/s3/s3.go b/internal/s3/s3.go
index 7f1ac27..a06cc43 100644
--- a/internal/s3/s3.go
+++ b/internal/s3/s3.go
@@ -15,7 +15,12 @@ type ObjectReader interface {
 }
 
 type S3 interface {
+	// Get the object from the S3 bucket. Returns an error if the object does not exist.
 	GetObject(ctx context.Context, key string) (ObjectReader, error)
+
+	// Check if the given key exists
 	KeyExists(ctx context.Context, key string) (bool, error)
+
+	// Get object metadata. The `Filename` field is optional. Returns nil if the object does not exist.
 	GetObjectMetadata(ctx context.Context, key string) (*types.Metadata, error)
 }