diff --git a/src/turnkey/conversions.rs b/src/turnkey/conversions.rs
index 6c73647..f991dd2 100644
--- a/src/turnkey/conversions.rs
+++ b/src/turnkey/conversions.rs
@@ -2,9 +2,49 @@
 //
 // SPDX-License-Identifier: MIT
 
+//! Conversions from Turnkey domain errors to [`AppError`].
+//!
+//! This module provides [`From`] trait implementations for converting
+//! Turnkey-specific errors into the canonical application error types.
+//!
+//! # Conversions
+//!
+//! - [`TurnkeyErrorKind`] → [`AppErrorKind`]: Uses [`map_turnkey_kind`]
+//! - [`TurnkeyError`] → [`AppError`]: Preserves message and maps kind
+//!
+//! # Examples
+//!
+//! ```rust
+//! use masterror::{
+//!     AppError, AppErrorKind,
+//!     turnkey::{TurnkeyError, TurnkeyErrorKind}
+//! };
+//!
+//! let turnkey_err = TurnkeyError::new(TurnkeyErrorKind::Timeout, "operation timed out");
+//! let app_err: AppError = turnkey_err.into();
+//!
+//! assert_eq!(app_err.kind, AppErrorKind::Timeout);
+//! assert_eq!(app_err.message.as_deref(), Some("operation timed out"));
+//! ```
+
 use super::domain::{TurnkeyError, TurnkeyErrorKind, map_turnkey_kind};
 use crate::{AppError, AppErrorKind};
 
+/// Convert [`TurnkeyErrorKind`] to [`AppErrorKind`].
+///
+/// Uses [`map_turnkey_kind`] to perform the conversion.
+///
+/// # Examples
+///
+/// ```rust
+/// use masterror::{AppErrorKind, turnkey::TurnkeyErrorKind};
+///
+/// let kind: AppErrorKind = TurnkeyErrorKind::Timeout.into();
+/// assert_eq!(kind, AppErrorKind::Timeout);
+///
+/// let kind: AppErrorKind = TurnkeyErrorKind::Auth.into();
+/// assert_eq!(kind, AppErrorKind::Unauthorized);
+/// ```
 impl From<TurnkeyErrorKind> for AppErrorKind {
     #[inline]
     fn from(k: TurnkeyErrorKind) -> Self {
@@ -12,10 +52,28 @@ impl From<TurnkeyErrorKind> for AppErrorKind {
     }
 }
 
+/// Convert [`TurnkeyError`] to [`AppError`].
+///
+/// Preserves the error message and maps the kind using explicit constructors
+/// to maintain consistent transport-layer mapping.
+///
+/// # Examples
+///
+/// ```rust
+/// use masterror::{
+///     AppError, AppErrorKind,
+///     turnkey::{TurnkeyError, TurnkeyErrorKind}
+/// };
+///
+/// let turnkey_err = TurnkeyError::new(TurnkeyErrorKind::RateLimited, "quota exceeded");
+/// let app_err: AppError = turnkey_err.into();
+///
+/// assert_eq!(app_err.kind, AppErrorKind::RateLimited);
+/// assert_eq!(app_err.message.as_deref(), Some("quota exceeded"));
+/// ```
 impl From<TurnkeyError> for AppError {
     #[inline]
     fn from(e: TurnkeyError) -> Self {
-        // Prefer explicit constructors to keep transport mapping consistent.
         match e.kind {
             TurnkeyErrorKind::UniqueLabel => AppError::conflict(e.msg),
             TurnkeyErrorKind::RateLimited => AppError::rate_limited(e.msg),
@@ -26,3 +84,117 @@ impl From<TurnkeyError> for AppError {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn turnkey_error_kind_to_app_error_kind_unique_label() {
+        let kind: AppErrorKind = TurnkeyErrorKind::UniqueLabel.into();
+        assert_eq!(kind, AppErrorKind::Conflict);
+    }
+
+    #[test]
+    fn turnkey_error_kind_to_app_error_kind_rate_limited() {
+        let kind: AppErrorKind = TurnkeyErrorKind::RateLimited.into();
+        assert_eq!(kind, AppErrorKind::RateLimited);
+    }
+
+    #[test]
+    fn turnkey_error_kind_to_app_error_kind_timeout() {
+        let kind: AppErrorKind = TurnkeyErrorKind::Timeout.into();
+        assert_eq!(kind, AppErrorKind::Timeout);
+    }
+
+    #[test]
+    fn turnkey_error_kind_to_app_error_kind_auth() {
+        let kind: AppErrorKind = TurnkeyErrorKind::Auth.into();
+        assert_eq!(kind, AppErrorKind::Unauthorized);
+    }
+
+    #[test]
+    fn turnkey_error_kind_to_app_error_kind_network() {
+        let kind: AppErrorKind = TurnkeyErrorKind::Network.into();
+        assert_eq!(kind, AppErrorKind::Network);
+    }
+
+    #[test]
+    fn turnkey_error_kind_to_app_error_kind_service() {
+        let kind: AppErrorKind = TurnkeyErrorKind::Service.into();
+        assert_eq!(kind, AppErrorKind::Turnkey);
+    }
+
+    #[test]
+    fn turnkey_error_to_app_error_unique_label() {
+        let turnkey = TurnkeyError::new(TurnkeyErrorKind::UniqueLabel, "duplicate label");
+        let app: AppError = turnkey.into();
+        assert_eq!(app.kind, AppErrorKind::Conflict);
+        assert_eq!(app.message.as_deref(), Some("duplicate label"));
+    }
+
+    #[test]
+    fn turnkey_error_to_app_error_rate_limited() {
+        let turnkey = TurnkeyError::new(TurnkeyErrorKind::RateLimited, "quota exceeded");
+        let app: AppError = turnkey.into();
+        assert_eq!(app.kind, AppErrorKind::RateLimited);
+        assert_eq!(app.message.as_deref(), Some("quota exceeded"));
+    }
+
+    #[test]
+    fn turnkey_error_to_app_error_timeout() {
+        let turnkey = TurnkeyError::new(TurnkeyErrorKind::Timeout, "request timed out");
+        let app: AppError = turnkey.into();
+        assert_eq!(app.kind, AppErrorKind::Timeout);
+        assert_eq!(app.message.as_deref(), Some("request timed out"));
+    }
+
+    #[test]
+    fn turnkey_error_to_app_error_auth() {
+        let turnkey = TurnkeyError::new(TurnkeyErrorKind::Auth, "invalid credentials");
+        let app: AppError = turnkey.into();
+        assert_eq!(app.kind, AppErrorKind::Unauthorized);
+        assert_eq!(app.message.as_deref(), Some("invalid credentials"));
+    }
+
+    #[test]
+    fn turnkey_error_to_app_error_network() {
+        let turnkey = TurnkeyError::new(TurnkeyErrorKind::Network, "connection failed");
+        let app: AppError = turnkey.into();
+        assert_eq!(app.kind, AppErrorKind::Network);
+        assert_eq!(app.message.as_deref(), Some("connection failed"));
+    }
+
+    #[test]
+    fn turnkey_error_to_app_error_service() {
+        let turnkey = TurnkeyError::new(TurnkeyErrorKind::Service, "service error");
+        let app: AppError = turnkey.into();
+        assert_eq!(app.kind, AppErrorKind::Turnkey);
+        assert_eq!(app.message.as_deref(), Some("service error"));
+    }
+
+    #[test]
+    fn turnkey_error_with_empty_message() {
+        let turnkey = TurnkeyError::new(TurnkeyErrorKind::Network, "");
+        let app: AppError = turnkey.into();
+        assert_eq!(app.kind, AppErrorKind::Network);
+        assert_eq!(app.message.as_deref(), Some(""));
+    }
+
+    #[test]
+    fn turnkey_error_with_long_message() {
+        let long_msg = "a".repeat(1000);
+        let turnkey = TurnkeyError::new(TurnkeyErrorKind::Service, &long_msg);
+        let app: AppError = turnkey.into();
+        assert_eq!(app.kind, AppErrorKind::Turnkey);
+        assert_eq!(app.message.as_deref(), Some(long_msg.as_str()));
+    }
+
+    #[test]
+    fn turnkey_error_with_unicode_message() {
+        let turnkey = TurnkeyError::new(TurnkeyErrorKind::Auth, "Неверные учетные данные");
+        let app: AppError = turnkey.into();
+        assert_eq!(app.kind, AppErrorKind::Unauthorized);
+        assert_eq!(app.message.as_deref(), Some("Неверные учетные данные"));
+    }
+}