diff --git a/api/build.gradle.kts b/api/build.gradle.kts
index 186cfe8..cc041ed 100644
--- a/api/build.gradle.kts
+++ b/api/build.gradle.kts
@@ -7,7 +7,7 @@ plugins {
 dependencies {
     implementation(kotlin("stdlib"))
     api(project(":core"))
-    implementation(project(":storage"))
+    implementation(project(":service"))
     api(libs.ktor.server.core)
     api(libs.ktor.serialization)
     api(libs.kotlinx.coroutines.core)
diff --git a/api/src/main/kotlin/com/wbrawner/twigs/ApiUtils.kt b/api/src/main/kotlin/com/wbrawner/twigs/ApiUtils.kt
deleted file mode 100644
index cb186c9..0000000
--- a/api/src/main/kotlin/com/wbrawner/twigs/ApiUtils.kt
+++ /dev/null
@@ -1,62 +0,0 @@
-package com.wbrawner.twigs
-
-import com.wbrawner.twigs.model.Budget
-import com.wbrawner.twigs.model.Permission
-import com.wbrawner.twigs.model.Session
-import com.wbrawner.twigs.storage.BudgetRepository
-import com.wbrawner.twigs.storage.PermissionRepository
-import io.ktor.http.*
-import io.ktor.server.application.*
-import io.ktor.server.auth.*
-import io.ktor.server.response.*
-import io.ktor.util.pipeline.*
-
-suspend inline fun PipelineContext<Unit, ApplicationCall>.requireBudgetWithPermission(
-    permissionRepository: PermissionRepository,
-    userId: String,
-    budgetId: String?,
-    permission: Permission,
-    otherwise: () -> Unit
-) {
-    if (budgetId.isNullOrBlank()) {
-        errorResponse(HttpStatusCode.BadRequest, "budgetId is required")
-        return
-    }
-    permissionRepository.findAll(
-        userId = userId,
-        budgetIds = listOf(budgetId)
-    ).firstOrNull {
-        it.permission.isAtLeast(permission)
-    } ?: run {
-        errorResponse(HttpStatusCode.Forbidden, "Insufficient permissions on budget $budgetId")
-        otherwise()
-    }
-}
-
-suspend fun PipelineContext<Unit, ApplicationCall>.budgetWithPermission(
-    budgetRepository: BudgetRepository,
-    permissionRepository: PermissionRepository,
-    budgetId: String,
-    permission: Permission,
-    block: suspend (Budget) -> Unit
-) {
-    val session = call.principal<Session>()!!
-    val userPermission = permissionRepository.findAll(
-        userId = session.userId,
-        budgetIds = listOf(budgetId)
-    ).firstOrNull()
-    if (userPermission?.permission?.isAtLeast(permission) != true) {
-        errorResponse(HttpStatusCode.Forbidden)
-        return
-    }
-    block(budgetRepository.findAll(ids = listOf(budgetId)).first())
-}
-
-suspend inline fun PipelineContext<Unit, ApplicationCall>.errorResponse(
-    httpStatusCode: HttpStatusCode = HttpStatusCode.NotFound,
-    message: String? = null
-) {
-    message?.let {
-        call.respond(httpStatusCode, ErrorResponse(message))
-    } ?: call.respond(httpStatusCode)
-}
diff --git a/api/src/main/kotlin/com/wbrawner/twigs/BudgetRoutes.kt b/api/src/main/kotlin/com/wbrawner/twigs/BudgetRoutes.kt
index 2246830..3cc5898 100644
--- a/api/src/main/kotlin/com/wbrawner/twigs/BudgetRoutes.kt
+++ b/api/src/main/kotlin/com/wbrawner/twigs/BudgetRoutes.kt
@@ -1,11 +1,8 @@
 package com.wbrawner.twigs
 
-import com.wbrawner.twigs.model.Budget
-import com.wbrawner.twigs.model.Permission
 import com.wbrawner.twigs.model.Session
-import com.wbrawner.twigs.model.UserPermission
-import com.wbrawner.twigs.storage.BudgetRepository
-import com.wbrawner.twigs.storage.PermissionRepository
+import com.wbrawner.twigs.service.budget.BudgetRequest
+import com.wbrawner.twigs.service.budget.BudgetService
 import io.ktor.http.*
 import io.ktor.server.application.*
 import io.ktor.server.auth.*
@@ -13,111 +10,39 @@ import io.ktor.server.request.*
 import io.ktor.server.response.*
 import io.ktor.server.routing.*
 
-fun Application.budgetRoutes(
-    budgetRepository: BudgetRepository,
-    permissionRepository: PermissionRepository
-) {
+fun Application.budgetRoutes(budgetService: BudgetService) {
     routing {
         route("/api/budgets") {
             authenticate(optional = false) {
                 get {
-                    val session = call.principal<Session>()!!
-                    val budgetIds = permissionRepository.findAll(userId = session.userId).map { it.budgetId }
-                    if (budgetIds.isEmpty()) {
-                        call.respond(emptyList<BudgetResponse>())
-                        return@get
-                    }
-                    val budgets = budgetRepository.findAll(ids = budgetIds).map {
-                        BudgetResponse(it, permissionRepository.findAll(budgetIds = listOf(it.id)))
-                    }
-                    call.respond(budgets)
+                    val session = requireNotNull(call.principal<Session>()) { "session is required" }
+                    call.respond(budgetService.budgetsForUser(userId = session.userId))
                 }
 
                 get("/{id}") {
-                    budgetWithPermission(
-                        budgetRepository,
-                        permissionRepository,
-                        call.parameters["id"]!!,
-                        Permission.READ
-                    ) { budget ->
-                        val users = permissionRepository.findAll(budgetIds = listOf(budget.id))
-                        call.respond(BudgetResponse(budget, users))
-                    }
+                    val session = requireNotNull(call.principal<Session>()) { "session is required" }
+                    val budgetId = requireNotNull(call.parameters["id"]) { "budgetId is required" }
+                    call.respond(budgetService.budget(budgetId = budgetId, userId = session.userId))
                 }
 
                 post {
                     val session = call.principal<Session>()!!
                     val request = call.receive<BudgetRequest>()
-                    if (request.name.isNullOrBlank()) {
-                        errorResponse(HttpStatusCode.BadRequest, "Name cannot be empty or null")
-                        return@post
-                    }
-                    val budget = budgetRepository.save(
-                        Budget(
-                            name = request.name,
-                            description = request.description
-                        )
-                    )
-                    val users = request.users?.map {
-                        permissionRepository.save(
-                            UserPermission(
-                                budgetId = budget.id,
-                                userId = it.user,
-                                permission = it.permission
-                            )
-                        )
-                    }?.toMutableSet() ?: mutableSetOf()
-                    if (users.none { it.userId == session.userId }) {
-                        users.add(
-                            permissionRepository.save(
-                                UserPermission(
-                                    budgetId = budget.id,
-                                    userId = session.userId,
-                                    permission = Permission.OWNER
-                                )
-                            )
-                        )
-                    }
-                    call.respond(BudgetResponse(budget, users))
+                    call.respond(budgetService.save(request = request, userId = session.userId))
                 }
 
                 put("/{id}") {
-                    budgetWithPermission(
-                        budgetRepository,
-                        permissionRepository,
-                        call.parameters["id"]!!,
-                        Permission.MANAGE
-                    ) { budget ->
-                        val request = call.receive<BudgetRequest>()
-                        val name = request.name ?: budget.name
-                        val description = request.description ?: budget.description
-                        val users = request.users?.map {
-                            permissionRepository.save(UserPermission(budget.id, it.user, it.permission))
-                        } ?: permissionRepository.findAll(budgetIds = listOf(budget.id))
-                        permissionRepository.findAll(budgetIds = listOf(budget.id)).forEach {
-                            if (it.permission != Permission.OWNER && users.none { userPermission -> userPermission.userId == it.userId }) {
-                                permissionRepository.delete(it)
-                            }
-                        }
-                        call.respond(
-                            BudgetResponse(
-                                budgetRepository.save(budget.copy(name = name, description = description)),
-                                users
-                            )
-                        )
-                    }
+                    val session = requireNotNull(call.principal<Session>()) { "session was null" }
+                    val request = call.receive<BudgetRequest>()
+                    val budgetId = requireNotNull(call.parameters["id"]) { "budgetId is required" }
+                    call.respond(budgetService.save(request = request, userId = session.id, budgetId = budgetId))
                 }
 
                 delete("/{id}") {
-                    budgetWithPermission(
-                        budgetRepository,
-                        permissionRepository,
-                        budgetId = call.parameters["id"]!!,
-                        Permission.OWNER
-                    ) { budget ->
-                        budgetRepository.delete(budget)
-                        call.respond(HttpStatusCode.NoContent)
-                    }
+                    val session = requireNotNull(call.principal<Session>()) { "session was null" }
+                    val budgetId = requireNotNull(call.parameters["id"]) { "budgetId is required" }
+                    budgetService.delete(budgetId = budgetId, userId = session.userId)
+                    call.respond(HttpStatusCode.NoContent)
                 }
             }
         }
diff --git a/api/src/main/kotlin/com/wbrawner/twigs/CategoryRoutes.kt b/api/src/main/kotlin/com/wbrawner/twigs/CategoryRoutes.kt
index 2e3e9af..2cee3e7 100644
--- a/api/src/main/kotlin/com/wbrawner/twigs/CategoryRoutes.kt
+++ b/api/src/main/kotlin/com/wbrawner/twigs/CategoryRoutes.kt
@@ -3,6 +3,10 @@ package com.wbrawner.twigs
 import com.wbrawner.twigs.model.Category
 import com.wbrawner.twigs.model.Permission
 import com.wbrawner.twigs.model.Session
+import com.wbrawner.twigs.service.category.CategoryRequest
+import com.wbrawner.twigs.service.category.CategoryResponse
+import com.wbrawner.twigs.service.errorResponse
+import com.wbrawner.twigs.service.requireBudgetWithPermission
 import com.wbrawner.twigs.storage.CategoryRepository
 import com.wbrawner.twigs.storage.PermissionRepository
 import io.ktor.http.*
diff --git a/api/src/main/kotlin/com/wbrawner/twigs/ErrorResponse.kt b/api/src/main/kotlin/com/wbrawner/twigs/ErrorResponse.kt
deleted file mode 100644
index 4145f53..0000000
--- a/api/src/main/kotlin/com/wbrawner/twigs/ErrorResponse.kt
+++ /dev/null
@@ -1,6 +0,0 @@
-package com.wbrawner.twigs
-
-import kotlinx.serialization.Serializable
-
-@Serializable
-data class ErrorResponse(val message: String)
\ No newline at end of file
diff --git a/api/src/main/kotlin/com/wbrawner/twigs/RecurringTransactionRoutes.kt b/api/src/main/kotlin/com/wbrawner/twigs/RecurringTransactionRoutes.kt
index 32fb046..452a94a 100644
--- a/api/src/main/kotlin/com/wbrawner/twigs/RecurringTransactionRoutes.kt
+++ b/api/src/main/kotlin/com/wbrawner/twigs/RecurringTransactionRoutes.kt
@@ -3,6 +3,10 @@ package com.wbrawner.twigs
 import com.wbrawner.twigs.model.Permission
 import com.wbrawner.twigs.model.RecurringTransaction
 import com.wbrawner.twigs.model.Session
+import com.wbrawner.twigs.service.errorResponse
+import com.wbrawner.twigs.service.recurringtransaction.RecurringTransactionRequest
+import com.wbrawner.twigs.service.recurringtransaction.asResponse
+import com.wbrawner.twigs.service.requireBudgetWithPermission
 import com.wbrawner.twigs.storage.PermissionRepository
 import com.wbrawner.twigs.storage.RecurringTransactionRepository
 import io.ktor.http.*
diff --git a/api/src/main/kotlin/com/wbrawner/twigs/TransactionRoutes.kt b/api/src/main/kotlin/com/wbrawner/twigs/TransactionRoutes.kt
index d918903..61bb24b 100644
--- a/api/src/main/kotlin/com/wbrawner/twigs/TransactionRoutes.kt
+++ b/api/src/main/kotlin/com/wbrawner/twigs/TransactionRoutes.kt
@@ -3,6 +3,10 @@ package com.wbrawner.twigs
 import com.wbrawner.twigs.model.Permission
 import com.wbrawner.twigs.model.Session
 import com.wbrawner.twigs.model.Transaction
+import com.wbrawner.twigs.service.errorResponse
+import com.wbrawner.twigs.service.requireBudgetWithPermission
+import com.wbrawner.twigs.service.transaction.BalanceResponse
+import com.wbrawner.twigs.service.transaction.TransactionRequest
 import com.wbrawner.twigs.storage.PermissionRepository
 import com.wbrawner.twigs.storage.TransactionRepository
 import io.ktor.http.*
diff --git a/api/src/main/kotlin/com/wbrawner/twigs/UserRoutes.kt b/api/src/main/kotlin/com/wbrawner/twigs/UserRoutes.kt
index c4ea8e6..083072a 100644
--- a/api/src/main/kotlin/com/wbrawner/twigs/UserRoutes.kt
+++ b/api/src/main/kotlin/com/wbrawner/twigs/UserRoutes.kt
@@ -3,6 +3,11 @@ package com.wbrawner.twigs
 import com.wbrawner.twigs.model.PasswordResetToken
 import com.wbrawner.twigs.model.Session
 import com.wbrawner.twigs.model.User
+import com.wbrawner.twigs.service.errorResponse
+import com.wbrawner.twigs.service.user.LoginRequest
+import com.wbrawner.twigs.service.user.PasswordResetRequest
+import com.wbrawner.twigs.service.user.ResetPasswordRequest
+import com.wbrawner.twigs.service.user.UserRequest
 import com.wbrawner.twigs.storage.*
 import io.ktor.http.*
 import io.ktor.server.application.*
diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
index a457969..10a4eb2 100644
--- a/gradle/libs.versions.toml
+++ b/gradle/libs.versions.toml
@@ -29,6 +29,7 @@ ktor-server-cio = { module = "io.ktor:ktor-server-cio", version.ref = "ktor" }
 ktor-server-content-negotiation = { module = "io.ktor:ktor-server-content-negotiation", version.ref = "ktor" }
 ktor-server-core = { module = "io.ktor:ktor-server-core", version.ref = "ktor" }
 ktor-server-cors = { module = "io.ktor:ktor-server-cors", version.ref = "ktor" }
+ktor-server-html = { module = "io.ktor:ktor-server-html-builder", version.ref = "ktor" }
 ktor-server-sessions = { module = "io.ktor:ktor-server-sessions", version.ref = "ktor" }
 ktor-server-test = { module = "io.ktor:ktor-server-test-host", version.ref = "ktor" }
 logback = { module = "ch.qos.logback:logback-classic", version.ref = "logback" }
diff --git a/service/build.gradle.kts b/service/build.gradle.kts
new file mode 100644
index 0000000..191bf56
--- /dev/null
+++ b/service/build.gradle.kts
@@ -0,0 +1,19 @@
+plugins {
+    `java-library`
+    alias(libs.plugins.kotlin.jvm)
+    alias(libs.plugins.kotlin.serialization)
+}
+
+dependencies {
+    implementation(kotlin("stdlib"))
+    api(libs.ktor.server.core)
+    implementation(project(":storage"))
+    api(libs.ktor.serialization)
+    api(libs.kotlinx.coroutines.core)
+    testImplementation(libs.junit.jupiter.api)
+    testRuntimeOnly(libs.junit.jupiter.engine)
+}
+
+tasks.getByName<Test>("test") {
+    useJUnitPlatform()
+}
\ No newline at end of file
diff --git a/service/src/main/java/com/wbrawner/twigs/service/ApiUtils.kt b/service/src/main/java/com/wbrawner/twigs/service/ApiUtils.kt
new file mode 100644
index 0000000..2d0e605
--- /dev/null
+++ b/service/src/main/java/com/wbrawner/twigs/service/ApiUtils.kt
@@ -0,0 +1,21 @@
+package com.wbrawner.twigs.service
+
+import com.wbrawner.twigs.model.Permission
+import com.wbrawner.twigs.service.budget.BudgetResponse
+import com.wbrawner.twigs.storage.BudgetRepository
+import com.wbrawner.twigs.storage.PermissionRepository
+import io.ktor.http.*
+
+suspend fun Pair<BudgetRepository, PermissionRepository>.budgetWithPermission(
+    userId: String,
+    budgetId: String,
+    permission: Permission
+): BudgetResponse {
+    val allPermissions = second.findAll(budgetIds = listOf(budgetId))
+    val userPermission = allPermissions.firstOrNull { it.userId == userId }
+        ?: throw HttpException(HttpStatusCode.NotFound)
+    if (!userPermission.permission.isAtLeast(permission)) {
+        throw HttpException(HttpStatusCode.Forbidden)
+    }
+    return BudgetResponse(first.findAll(ids = listOf(budgetId)).first(), allPermissions)
+}
\ No newline at end of file
diff --git a/service/src/main/java/com/wbrawner/twigs/service/ErrorResponse.kt b/service/src/main/java/com/wbrawner/twigs/service/ErrorResponse.kt
new file mode 100644
index 0000000..e08223d
--- /dev/null
+++ b/service/src/main/java/com/wbrawner/twigs/service/ErrorResponse.kt
@@ -0,0 +1,18 @@
+package com.wbrawner.twigs.service
+
+import io.ktor.http.*
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class ErrorResponse(val message: String)
+
+class HttpException(
+    val statusCode: HttpStatusCode,
+    override val cause: Throwable? = null,
+    override val message: String? = null
+) : Throwable() {
+    constructor(statusCode: HttpStatusCode) : this(statusCode = statusCode, message = statusCode.description)
+
+    fun toResponse(): ErrorResponse =
+        ErrorResponse(requireNotNull(message) { "Cannot send error to client without message" })
+}
\ No newline at end of file
diff --git a/api/src/main/kotlin/com/wbrawner/twigs/BudgetApi.kt b/service/src/main/java/com/wbrawner/twigs/service/budget/BudgetApi.kt
similarity index 79%
rename from api/src/main/kotlin/com/wbrawner/twigs/BudgetApi.kt
rename to service/src/main/java/com/wbrawner/twigs/service/budget/BudgetApi.kt
index 1d83da9..bfc16a6 100644
--- a/api/src/main/kotlin/com/wbrawner/twigs/BudgetApi.kt
+++ b/service/src/main/java/com/wbrawner/twigs/service/budget/BudgetApi.kt
@@ -1,9 +1,10 @@
-package com.wbrawner.twigs
+package com.wbrawner.twigs.service.budget
 
 import com.wbrawner.twigs.model.Budget
 import com.wbrawner.twigs.model.UserPermission
+import com.wbrawner.twigs.service.user.UserPermissionRequest
+import com.wbrawner.twigs.service.user.UserPermissionResponse
 import kotlinx.serialization.Serializable
-import java.util.*
 
 @Serializable
 data class BudgetRequest(
@@ -20,7 +21,7 @@ data class BudgetResponse(
     val users: List<UserPermissionResponse>
 ) {
     constructor(budget: Budget, users: Iterable<UserPermission>) : this(
-        Objects.requireNonNull<String>(budget.id),
+        requireNotNull(budget.id),
         budget.name,
         budget.description,
         users.map { userPermission: UserPermission ->
diff --git a/service/src/main/java/com/wbrawner/twigs/service/budget/BudgetService.kt b/service/src/main/java/com/wbrawner/twigs/service/budget/BudgetService.kt
new file mode 100644
index 0000000..ec31e90
--- /dev/null
+++ b/service/src/main/java/com/wbrawner/twigs/service/budget/BudgetService.kt
@@ -0,0 +1,130 @@
+package com.wbrawner.twigs.service.budget
+
+import com.wbrawner.twigs.model.Budget
+import com.wbrawner.twigs.model.Permission
+import com.wbrawner.twigs.model.UserPermission
+import com.wbrawner.twigs.service.HttpException
+import com.wbrawner.twigs.service.budgetWithPermission
+import com.wbrawner.twigs.service.user.UserPermissionRequest
+import com.wbrawner.twigs.storage.BudgetRepository
+import com.wbrawner.twigs.storage.PermissionRepository
+import io.ktor.http.*
+
+interface BudgetService {
+    suspend fun budgetsForUser(userId: String): List<BudgetResponse>
+
+    suspend fun budget(budgetId: String, userId: String): BudgetResponse
+
+    suspend fun save(request: BudgetRequest, userId: String, budgetId: String? = null): BudgetResponse
+
+    suspend fun delete(budgetId: String, userId: String)
+}
+
+class DefaultBudgetService(
+    private val budgetRepository: BudgetRepository,
+    private val permissionRepository: PermissionRepository
+) : BudgetService {
+    private val budgetPermissionRepository = budgetRepository to permissionRepository
+    override suspend fun budgetsForUser(userId: String): List<BudgetResponse> {
+        val budgetIds = permissionRepository.findAll(userId = userId).map { it.budgetId }
+        if (budgetIds.isEmpty()) {
+            return emptyList()
+        }
+        return budgetRepository.findAll(ids = budgetIds).map {
+            BudgetResponse(it, permissionRepository.findAll(budgetIds = listOf(it.id)))
+        }
+    }
+
+    override suspend fun budget(budgetId: String, userId: String): BudgetResponse =
+        budgetPermissionRepository.budgetWithPermission(userId, budgetId, Permission.READ)
+
+    override suspend fun save(request: BudgetRequest, userId: String, budgetId: String?): BudgetResponse {
+        val budget = budgetId?.let {
+            budgetPermissionRepository.budgetWithPermission(
+                budgetId = it,
+                userId = userId,
+                permission = Permission.MANAGE
+            ).run {
+                Budget(
+                    id = it,
+                    name = request.name ?: name,
+                    description = request.description ?: description
+                )
+            }
+        } ?: run {
+            if (request.name.isNullOrBlank()) {
+                throw HttpException(HttpStatusCode.BadRequest, message = "Name cannot be empty or null")
+            }
+            Budget(
+                name = request.name,
+                description = request.description
+            )
+        }
+        val users = budgetId?.let {
+            // If user is owner, apply changes
+            // If user is manager, make sure they're not changing ownership
+            val oldUsers = permissionRepository.findAll(budgetIds = listOf(budgetId))
+            val oldPermissions = oldUsers.associate { it.userId to it.permission }
+            val currentUserPermission = oldPermissions[userId] ?: throw HttpException(HttpStatusCode.NotFound)
+            val newUsers = request.users?.map { userPermission ->
+                if (userPermission.permission == Permission.OWNER
+                    && oldPermissions[userPermission.user] !== Permission.OWNER
+                    && currentUserPermission != Permission.OWNER
+                ) {
+                    // The user is attempting to add a new owner
+                    throw HttpException(
+                        HttpStatusCode.Forbidden,
+                        message = "You must be an owner to be able to modify other users' ownership"
+                    )
+                }
+                userPermission
+            } ?: return@let oldUsers.map { UserPermissionRequest(it.userId, it.permission) }
+            oldPermissions.filterValues { it == Permission.OWNER }
+                .forEach { (user, permission) ->
+                    if (newUsers.none { it.user == user && it.permission == permission }
+                        && currentUserPermission != Permission.OWNER
+                    ) {
+                        // The user is attempting to remove a previous owner
+                        throw HttpException(
+                            HttpStatusCode.Forbidden,
+                            message = "You must be an owner to be able to modify other users' ownership"
+                        )
+                    }
+                }
+            oldUsers.forEach { oldUserPermission ->
+                if (newUsers.none { it.user == oldUserPermission.userId && it.permission == oldUserPermission.permission }) {
+                    permissionRepository.delete(oldUserPermission)
+                }
+            }
+            newUsers
+        } ?: run {
+            val newUsers = request.users
+                ?.toMutableList()
+                ?: mutableListOf()
+            val currentUserPermission = newUsers.firstOrNull { it.user == userId }
+            if (currentUserPermission == null || currentUserPermission.permission != Permission.OWNER) {
+                newUsers.removeIf { it.user == userId }
+                newUsers.add(UserPermissionRequest(userId, Permission.OWNER))
+            }
+            newUsers
+        }
+        val savedBudget = budgetRepository.save(budget)
+        return BudgetResponse(
+            savedBudget,
+            users.map {
+                permissionRepository.save(
+                    UserPermission(
+                        budgetId = savedBudget.id,
+                        userId = it.user,
+                        permission = it.permission
+                    )
+                )
+            }
+        )
+    }
+
+    override suspend fun delete(budgetId: String, userId: String) {
+        val budgetResponse = budgetPermissionRepository.budgetWithPermission(userId, budgetId, Permission.OWNER)
+        budgetRepository.delete(Budget(budgetResponse.id, budgetResponse.name, budgetResponse.description))
+    }
+}
\ No newline at end of file
diff --git a/api/src/main/kotlin/com/wbrawner/twigs/CategoryApi.kt b/service/src/main/java/com/wbrawner/twigs/service/category/CategoryApi.kt
similarity index 94%
rename from api/src/main/kotlin/com/wbrawner/twigs/CategoryApi.kt
rename to service/src/main/java/com/wbrawner/twigs/service/category/CategoryApi.kt
index 18427fb..d88e47a 100644
--- a/api/src/main/kotlin/com/wbrawner/twigs/CategoryApi.kt
+++ b/service/src/main/java/com/wbrawner/twigs/service/category/CategoryApi.kt
@@ -1,4 +1,4 @@
-package com.wbrawner.twigs
+package com.wbrawner.twigs.service.category
 
 import com.wbrawner.twigs.model.Category
 import kotlinx.serialization.Serializable
diff --git a/api/src/main/kotlin/com/wbrawner/twigs/RecurringTransactionsApi.kt b/service/src/main/java/com/wbrawner/twigs/service/recurringtransaction/RecurringTransactionsApi.kt
similarity index 95%
rename from api/src/main/kotlin/com/wbrawner/twigs/RecurringTransactionsApi.kt
rename to service/src/main/java/com/wbrawner/twigs/service/recurringtransaction/RecurringTransactionsApi.kt
index 3bc7542..cdf1825 100644
--- a/api/src/main/kotlin/com/wbrawner/twigs/RecurringTransactionsApi.kt
+++ b/service/src/main/java/com/wbrawner/twigs/service/recurringtransaction/RecurringTransactionsApi.kt
@@ -1,4 +1,4 @@
-package com.wbrawner.twigs
+package com.wbrawner.twigs.service.recurringtransaction
 
 import com.wbrawner.twigs.model.RecurringTransaction
 import kotlinx.serialization.Serializable
diff --git a/api/src/main/kotlin/com/wbrawner/twigs/TransactionApi.kt b/service/src/main/java/com/wbrawner/twigs/service/transaction/TransactionApi.kt
similarity index 95%
rename from api/src/main/kotlin/com/wbrawner/twigs/TransactionApi.kt
rename to service/src/main/java/com/wbrawner/twigs/service/transaction/TransactionApi.kt
index 4062858..130319d 100644
--- a/api/src/main/kotlin/com/wbrawner/twigs/TransactionApi.kt
+++ b/service/src/main/java/com/wbrawner/twigs/service/transaction/TransactionApi.kt
@@ -1,4 +1,4 @@
-package com.wbrawner.twigs
+package com.wbrawner.twigs.service.transaction
 
 import com.wbrawner.twigs.model.Transaction
 import kotlinx.serialization.Serializable
diff --git a/api/src/main/kotlin/com/wbrawner/twigs/UserApi.kt b/service/src/main/java/com/wbrawner/twigs/service/user/UserApi.kt
similarity index 97%
rename from api/src/main/kotlin/com/wbrawner/twigs/UserApi.kt
rename to service/src/main/java/com/wbrawner/twigs/service/user/UserApi.kt
index f8e9f91..7443a51 100644
--- a/api/src/main/kotlin/com/wbrawner/twigs/UserApi.kt
+++ b/service/src/main/java/com/wbrawner/twigs/service/user/UserApi.kt
@@ -1,4 +1,4 @@
-package com.wbrawner.twigs
+package com.wbrawner.twigs.service.user
 
 import com.wbrawner.twigs.model.PasswordResetToken
 import com.wbrawner.twigs.model.Permission
diff --git a/settings.gradle.kts b/settings.gradle.kts
index a1af3bb..f54ab1e 100644
--- a/settings.gradle.kts
+++ b/settings.gradle.kts
@@ -1,3 +1,4 @@
 rootProject.name = "twigs"
 include("core", "api", "app", "storage", "db", "web")
-include("testhelpers")
\ No newline at end of file
+include("testhelpers")
+include("service")
diff --git a/web/build.gradle.kts b/web/build.gradle.kts
index 40bd3cb..502837e 100644
--- a/web/build.gradle.kts
+++ b/web/build.gradle.kts
@@ -8,6 +8,7 @@ plugins {
 dependencies {
     implementation(kotlin("stdlib"))
     api(libs.ktor.server.core)
+    implementation(libs.ktor.server.html)
     testImplementation(libs.junit.jupiter.api)
     testRuntimeOnly(libs.junit.jupiter.engine)
 }