diff --git a/Sources/Swift/Integrations/SessionReplay/SentryReplayNetworkDetails.swift b/Sources/Swift/Integrations/SessionReplay/SentryReplayNetworkDetails.swift
new file mode 100644
index 0000000000..8751456864
--- /dev/null
+++ b/Sources/Swift/Integrations/SessionReplay/SentryReplayNetworkDetails.swift
@@ -0,0 +1,158 @@
+import Foundation
+
+/// Warning codes for network body capture issues.
+///
+/// Raw values must match the frontend constants so the Sentry UI renders the correct warnings.
+/// - SeeAlso: https://github.com/getsentry/sentry/blob/8b79857b2eff86f4df2f3abaf1e46c74893e3781/static/app/utils/replays/replay.tsx#L5
+enum NetworkBodyWarning: String {
+    case jsonTruncated = "JSON_TRUNCATED"
+    case textTruncated = "TEXT_TRUNCATED"
+    case invalidJson = "INVALID_JSON"
+    case bodyParseError = "BODY_PARSE_ERROR"
+}
+
+/// Main container for network request/response tracking.
+///
+/// ObjC callers (SentryNetworkTracker) create this object and populate it
+/// via `setRequest`/`setResponse`. Swift callers (SentrySRDefaultBreadcrumbConverter)
+/// consume it via `serialize()`.
+@objc
+@_spi(Private) public class SentryReplayNetworkDetails: NSObject {
+
+    // MARK: - Nested Types (Swift-only)
+
+    /// Typed representation of captured body content.
+    enum BodyContent {
+        /// Parsed JSON body (dictionary or array).
+        case json(Any)
+        /// Text body (plain text, HTML, XML, etc.).
+        case text(String)
+
+        init(_ value: Any) {
+            if let string = value as? String {
+                self = .text(string)
+            } else {
+                self = .json(value)
+            }
+        }
+
+        var serializedValue: Any {
+            switch self {
+            case .json(let value): return value
+            case .text(let string): return string
+            }
+        }
+    }
+
+    /// Captured request or response body with optional parsing warnings.
+    struct Body {
+        let content: BodyContent
+        let warnings: [NetworkBodyWarning]
+
+        init(content: Any, warnings: [NetworkBodyWarning] = []) {
+            self.content = BodyContent(content)
+            self.warnings = warnings
+        }
+
+        func serialize() -> [String: Any] {
+            var result = [String: Any]()
+            result["body"] = content.serializedValue
+            if !warnings.isEmpty {
+                result["warnings"] = warnings.map(\.rawValue)
+            }
+            return result
+        }
+    }
+
+    /// Captured HTTP request or response details (size, body, headers).
+    struct Detail {
+        let size: NSNumber?
+        let body: Body?
+        let headers: [String: String]
+
+        func serialize() -> [String: Any] {
+            var result = [String: Any]()
+            if let size { result["size"] = size }
+            if let body { result["body"] = body.serialize() }
+            if !headers.isEmpty { result["headers"] = headers }
+            return result
+        }
+    }
+
+    // MARK: - Properties
+
+    /// Key used to store network details in breadcrumb data dictionary.
+    @objc public static let replayNetworkDetailsKey = "_networkDetails"
+
+    private(set) var method: String?
+    private(set) var statusCode: NSNumber?
+    private(set) var request: Detail?
+    private(set) var response: Detail?
+
+    /// Request body size in bytes, derived from request details.
+    var requestBodySize: NSNumber? { request?.size }
+
+    /// Response body size in bytes, derived from response details.
+    var responseBodySize: NSNumber? { response?.size }
+
+    // MARK: - Initialization
+
+    /// Creates a new instance with the given HTTP method.
+    @objc
+    public init(method: String?) {
+        self.method = method
+        super.init()
+    }
+
+    // MARK: - ObjC Setters
+
+    /// Sets request details from raw components.
+    ///
+    /// - Parameters:
+    ///   - size: Request body size in bytes, or nil if unknown.
+    ///   - body: Pre-parsed body content (dictionary, array, or string), or nil if not captured.
+    ///   - headers: Filtered HTTP request headers.
+    @objc
+    public func setRequest(size: NSNumber?, body: Any?, headers: [String: String]) {
+        self.request = Detail(
+            size: size,
+            body: body.map { Body(content: $0) },
+            headers: headers
+        )
+    }
+
+    /// Sets response details from raw components.
+    ///
+    /// - Parameters:
+    ///   - statusCode: HTTP status code.
+    ///   - size: Response body size in bytes, or nil if unknown.
+    ///   - body: Pre-parsed body content (dictionary, array, or string), or nil if not captured.
+    ///   - headers: Filtered HTTP response headers.
+    @objc
+    public func setResponse(statusCode: Int, size: NSNumber?, body: Any?, headers: [String: String]) {
+        self.statusCode = NSNumber(value: statusCode)
+        self.response = Detail(
+            size: size,
+            body: body.map { Body(content: $0) },
+            headers: headers
+        )
+    }
+
+    // MARK: - Serialization
+
+    /// Serializes to dictionary for inclusion in breadcrumb data.
+    public func serialize() -> [String: Any] {
+        var result = [String: Any]()
+        if let method { result["method"] = method }
+        if let statusCode { result["statusCode"] = statusCode }
+        if let requestBodySize { result["requestBodySize"] = requestBodySize }
+        if let responseBodySize { result["responseBodySize"] = responseBodySize }
+        if let request { result["request"] = request.serialize() }
+        if let response { result["response"] = response.serialize() }
+        return result
+    }
+
+    public override var description: String {
+        "SentryReplayNetworkDetails: \(serialize())"
+    }
+}
diff --git a/Sources/Swift/Integrations/SessionReplay/SentryReplayOptions.swift b/Sources/Swift/Integrations/SessionReplay/SentryReplayOptions.swift
index 82c18bda9b..4121dcb78b 100644
--- a/Sources/Swift/Integrations/SessionReplay/SentryReplayOptions.swift
+++ b/Sources/Swift/Integrations/SessionReplay/SentryReplayOptions.swift
@@ -715,17 +715,14 @@ public class SentryReplayOptions: NSObject, SentryRedactOptions {
      *
      * - Parameter userHeaders: Headers specified by the user (can be nil)
      * - Parameter defaults: Default headers that must always be included
-     * - Returns: Array containing both user headers and default headers (with duplicates removed)
+     * - Returns: Array containing both user headers and default headers with duplicates removed.
      */
     private static func mergeWithDefaultHeaders(_ userHeaders: [String]?, defaults: [String]) -> [String] {
         let providedHeaders = userHeaders ?? []
         
-        // Use Set to remove duplicates, then convert back to Array
-        // Case-insensitive comparison to avoid duplicate headers with different casing
         var seenHeaders = Set<String>()
         var result: [String] = []
-        
-        // Add default headers first
+
         for header in defaults {
             let lowercased = header.lowercased()
             if !seenHeaders.contains(lowercased) {
@@ -733,8 +730,7 @@ public class SentryReplayOptions: NSObject, SentryRedactOptions {
                 result.append(header)
             }
         }
-        
-        // Add user-provided headers
+
         for header in providedHeaders {
             let lowercased = header.lowercased()
             if !seenHeaders.contains(lowercased) {