diff --git a/Package.resolved b/Package.resolved
index d9823ed..fab81b6 100644
--- a/Package.resolved
+++ b/Package.resolved
@@ -1,6 +1,15 @@
 {
-  "originHash" : "65db2e61c18e81132241ea93ca8a61c58429030954e6c853d3720afa9aeab01c",
+  "originHash" : "090c675500195d294a5f4987351db53f4409bd98981b45c7a1f34a60685e39b7",
   "pins" : [
+    {
+      "identity" : "anycodable",
+      "kind" : "remoteSourceControl",
+      "location" : "https://github.com/Flight-School/AnyCodable",
+      "state" : {
+        "revision" : "69261f239f0fffaf51495dadc4f8483fbfe97025",
+        "version" : "0.6.1"
+      }
+    },
     {
       "identity" : "swiftlintplugins",
       "kind" : "remoteSourceControl",
diff --git a/Package.swift b/Package.swift
index 9074893..72867e9 100644
--- a/Package.swift
+++ b/Package.swift
@@ -14,6 +14,7 @@ let package = Package(
     ],
     dependencies: [
         // Dependencies declare other packages that this package depends on.
+        .package(url: "https://github.com/Flight-School/AnyCodable", exact: "0.6.1"),
         .package(url: "https://github.com/SimplyDanny/SwiftLintPlugins", exact: "0.55.1")
     ],
     targets: [
@@ -21,6 +22,7 @@ let package = Package(
         // Targets can depend on other targets in this package and products from dependencies.
         .target(
             name: "Passage",
+            dependencies: ["AnyCodable"],
             plugins: [.plugin(name: "SwiftLintBuildToolPlugin", package: "SwiftLintPlugins")]
         ),
         .testTarget(
diff --git a/Sources/Passage/errors/PassageAppError.swift b/Sources/Passage/errors/PassageAppError.swift
new file mode 100644
index 0000000..051d5ef
--- /dev/null
+++ b/Sources/Passage/errors/PassageAppError.swift
@@ -0,0 +1,38 @@
+import Foundation
+
+public enum PassageAppError: PassageError {
+    
+    case appNotFound(message: String)
+    case invalidRequest(message: String)
+    case unspecified(message: String)
+    
+    public var errorDescription: String {
+        switch self {
+        case .appNotFound(let message),
+             .invalidRequest(let message),
+             .unspecified(let message):
+            return message
+        }
+    }
+    
+    public static func convert(error: Error) -> PassageAppError {
+        // Check if error is already proper
+        if let passageAppError = error as? PassageAppError {
+            return passageAppError
+        }
+        // Handle client error
+        if let errorResponse = error as? ErrorResponse,
+           let (_, errorData) = PassageErrorData.getData(from: errorResponse)
+        {
+            switch errorData.code {
+            case Model404Code.appNotFound.rawValue:
+                return .appNotFound(message: errorData.error)
+            case Model400Code.request.rawValue:
+                return .invalidRequest(message: errorData.error)
+            default: ()
+            }
+        }
+        return .unspecified(message: "unspecified error")
+    }
+    
+}
diff --git a/Sources/Passage/errors/PassageError.swift b/Sources/Passage/errors/PassageError.swift
new file mode 100644
index 0000000..4cd77af
--- /dev/null
+++ b/Sources/Passage/errors/PassageError.swift
@@ -0,0 +1,21 @@
+import Foundation
+
+public protocol PassageError: Error, LocalizedError {
+    static func convert(error: Error) -> Self
+    var errorDescription: String { get }
+}
+
+struct PassageErrorData: Codable {
+    let code: String
+    let error: String
+    
+    static func getData(from errorResponse: ErrorResponse) -> (Int, PassageErrorData)? {
+        guard
+            case let ErrorResponse.error(statusCode, data?, _, _) = errorResponse,
+            let errorData = try? JSONDecoder().decode(PassageErrorData.self, from: data)
+        else {
+            return nil
+        }
+        return (statusCode, errorData)
+    }
+}
diff --git a/Sources/Passage/interfaces/PassageApp.swift b/Sources/Passage/interfaces/PassageApp.swift
new file mode 100644
index 0000000..3d97cf9
--- /dev/null
+++ b/Sources/Passage/interfaces/PassageApp.swift
@@ -0,0 +1,75 @@
+import AnyCodable
+
+/// A class representing the Passage application, allowing interaction with the application's API.
+public class PassageApp {
+    
+    private let appId: String
+    
+    init(appId: String) {
+        self.appId = appId
+    }
+    
+    /// Fetches information about the Passage app.
+    /// - Returns: A PassageAppInfo struct containing the app's details.
+    /// - Throws: `PassageAppError` if the API call fails.
+    public func info() async throws -> PassageAppInfo {
+        do {
+           let appInfoResponse = try await AppsAPI.getApp(appId: appId)
+           return appInfoResponse.app
+       } catch {
+           throw PassageAppError.convert(error: error)
+       }
+    }
+    
+    /// Checks if a user exists for a given identifier.
+    ///
+    /// - Parameter identifier: The identifier (e.g., email or phone number) to check for existence.
+    /// - Returns: A PublicUserInfo struct if the user exists, or `nil` if not.
+    /// - Throws: `PassageAppError` if the request is invalid or an error occurs during the API call.
+    public func userExists(identifier: String) async throws -> PublicUserInfo? {
+        do {
+            guard let safeId = identifier
+                .addingPercentEncoding(withAllowedCharacters: .alphanumerics)
+            else {
+                throw PassageAppError.invalidRequest(message: "invalid identifier")
+            }
+            let response = try await UsersAPI
+                .checkUserIdentifier(
+                    appId: appId,
+                    identifier: safeId
+                )
+            return response.user
+        } catch {
+            throw PassageAppError.convert(error: error)
+        }
+    }
+    
+    /// Creates a new user with the specified identifier and optional metadata.
+    /// - Parameters:
+    ///   - identifier: The identifier (e.g., email or  phone number) for the new user.
+    ///   - userMetadata: Optional metadata to associate with the user.
+    /// - Returns: A PublicUserInfo struct representing the newly created user.
+    /// - Throws: `PassageAppError` if an error occurs during user creation or the API call fails.
+    public func createUser(
+        identifier: String,
+        userMetadata: AnyCodable? = nil
+    ) async throws -> PublicUserInfo {
+        do {
+            let params = CreateUserParams(
+                identifier: identifier,
+                userMetadata: userMetadata
+            )
+            let resposne = try await UsersAPI.createUser(
+                appId: appId,
+                createUserParams: params
+            )
+            guard let user = resposne.user else {
+                throw PassageAppError.invalidRequest(message: "invalid request")
+            }
+            return user
+        } catch {
+            throw PassageAppError.convert(error: error)
+        }
+    }
+    
+}
diff --git a/Sources/Passage/typealiases/PassageAppInfo.swift b/Sources/Passage/typealiases/PassageAppInfo.swift
new file mode 100644
index 0000000..9a97f2b
--- /dev/null
+++ b/Sources/Passage/typealiases/PassageAppInfo.swift
@@ -0,0 +1 @@
+public typealias PassageAppInfo = App
diff --git a/Sources/Passage/typealiases/PublicUserInfo.swift b/Sources/Passage/typealiases/PublicUserInfo.swift
new file mode 100644
index 0000000..1d09426
--- /dev/null
+++ b/Sources/Passage/typealiases/PublicUserInfo.swift
@@ -0,0 +1 @@
+public typealias PublicUserInfo = User