Add RSVP creation endpoint with typed tokens and attendee count

Introduce typed token value objects (EventToken, OrganizerToken,
RsvpToken) and refactor all existing Event code to use them.

Add POST /events/{token}/rsvps endpoint that persists an RSVP and
returns an rsvpToken. Populate attendeeCount in GET /events/{token}
from a real count query instead of hardcoded 0.

Includes: OpenAPI spec, Liquibase migration (rsvps table with
ON DELETE CASCADE), domain model, hexagonal ports/adapters,
service layer, and full test coverage (unit + integration).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/main/java/de/fete/adapter/in/web/EventController.java

@@ -3,13 +3,19 @@ package de.fete.adapter.in.web;
 import de.fete.adapter.in.web.api.EventsApi;
 import de.fete.adapter.in.web.model.CreateEventRequest;
 import de.fete.adapter.in.web.model.CreateEventResponse;
+import de.fete.adapter.in.web.model.CreateRsvpRequest;
+import de.fete.adapter.in.web.model.CreateRsvpResponse;
 import de.fete.adapter.in.web.model.GetEventResponse;
 import de.fete.application.service.EventNotFoundException;
 import de.fete.application.service.InvalidTimezoneException;
 import de.fete.domain.model.CreateEventCommand;
 import de.fete.domain.model.Event;
+import de.fete.domain.model.EventToken;
+import de.fete.domain.model.Rsvp;
 import de.fete.domain.port.in.CreateEventUseCase;
+import de.fete.domain.port.in.CreateRsvpUseCase;
 import de.fete.domain.port.in.GetEventUseCase;
+import de.fete.domain.port.out.RsvpRepository;
 import java.time.Clock;
 import java.time.DateTimeException;
 import java.time.LocalDate;
@@ -25,15 +31,21 @@ public class EventController implements EventsApi {
 
   private final CreateEventUseCase createEventUseCase;
   private final GetEventUseCase getEventUseCase;
+  private final CreateRsvpUseCase createRsvpUseCase;
+  private final RsvpRepository rsvpRepository;
   private final Clock clock;
 
-  /** Creates a new controller with the given use cases and clock. */
+  /** Creates a new controller with the given use cases, repository, and clock. */
   public EventController(
       CreateEventUseCase createEventUseCase,
       GetEventUseCase getEventUseCase,
+      CreateRsvpUseCase createRsvpUseCase,
+      RsvpRepository rsvpRepository,
       Clock clock) {
     this.createEventUseCase = createEventUseCase;
     this.getEventUseCase = getEventUseCase;
+    this.createRsvpUseCase = createRsvpUseCase;
+    this.rsvpRepository = rsvpRepository;
     this.clock = clock;
   }
 
@@ -54,8 +66,8 @@ public class EventController implements EventsApi {
     Event event = createEventUseCase.createEvent(command);
 
     var response = new CreateEventResponse();
-    response.setEventToken(event.getEventToken());
-    response.setOrganizerToken(event.getOrganizerToken());
+    response.setEventToken(event.getEventToken().value());
+    response.setOrganizerToken(event.getOrganizerToken().value());
     response.setTitle(event.getTitle());
     response.setDateTime(event.getDateTime());
     response.setTimezone(event.getTimezone().getId());
@@ -66,23 +78,38 @@ public class EventController implements EventsApi {
 
   @Override
   public ResponseEntity<GetEventResponse> getEvent(UUID token) {
-    Event event = getEventUseCase.getByEventToken(token)
+    var eventToken = new de.fete.domain.model.EventToken(token);
+    Event event = getEventUseCase.getByEventToken(eventToken)
         .orElseThrow(() -> new EventNotFoundException(token));
 
     var response = new GetEventResponse();
-    response.setEventToken(event.getEventToken());
+    response.setEventToken(event.getEventToken().value());
     response.setTitle(event.getTitle());
     response.setDescription(event.getDescription());
     response.setDateTime(event.getDateTime());
     response.setTimezone(event.getTimezone().getId());
     response.setLocation(event.getLocation());
-    response.setAttendeeCount(0);
+    response.setAttendeeCount(
+        (int) rsvpRepository.countByEventId(event.getId()));
     response.setExpired(
         event.getExpiryDate().isBefore(LocalDate.now(clock)));
 
     return ResponseEntity.ok(response);
   }
 
+  @Override
+  public ResponseEntity<CreateRsvpResponse> createRsvp(
+      UUID token, CreateRsvpRequest createRsvpRequest) {
+    var eventToken = new EventToken(token);
+    Rsvp rsvp = createRsvpUseCase.createRsvp(eventToken, createRsvpRequest.getName());
+
+    var response = new CreateRsvpResponse();
+    response.setRsvpToken(rsvp.getRsvpToken().value());
+    response.setName(rsvp.getName());
+
+    return ResponseEntity.status(HttpStatus.CREATED).body(response);
+  }
+
   private static ZoneId parseTimezone(String timezone) {
     try {
       return ZoneId.of(timezone);

backend/src/main/java/de/fete/adapter/out/persistence/EventPersistenceAdapter.java

@@ -1,10 +1,11 @@
 package de.fete.adapter.out.persistence;
 
 import de.fete.domain.model.Event;
+import de.fete.domain.model.EventToken;
+import de.fete.domain.model.OrganizerToken;
 import de.fete.domain.port.out.EventRepository;
 import java.time.ZoneId;
 import java.util.Optional;
-import java.util.UUID;
 import org.springframework.stereotype.Repository;
 
 /** Persistence adapter implementing the EventRepository outbound port. */
@@ -26,15 +27,15 @@ public class EventPersistenceAdapter implements EventRepository {
   }
 
   @Override
-  public Optional<Event> findByEventToken(UUID eventToken) {
-    return jpaRepository.findByEventToken(eventToken).map(this::toDomain);
+  public Optional<Event> findByEventToken(EventToken eventToken) {
+    return jpaRepository.findByEventToken(eventToken.value()).map(this::toDomain);
   }
 
   private EventJpaEntity toEntity(Event event) {
     var entity = new EventJpaEntity();
     entity.setId(event.getId());
-    entity.setEventToken(event.getEventToken());
-    entity.setOrganizerToken(event.getOrganizerToken());
+    entity.setEventToken(event.getEventToken().value());
+    entity.setOrganizerToken(event.getOrganizerToken().value());
     entity.setTitle(event.getTitle());
     entity.setDescription(event.getDescription());
     entity.setDateTime(event.getDateTime());
@@ -48,8 +49,8 @@ public class EventPersistenceAdapter implements EventRepository {
   private Event toDomain(EventJpaEntity entity) {
     var event = new Event();
     event.setId(entity.getId());
-    event.setEventToken(entity.getEventToken());
-    event.setOrganizerToken(entity.getOrganizerToken());
+    event.setEventToken(new EventToken(entity.getEventToken()));
+    event.setOrganizerToken(new OrganizerToken(entity.getOrganizerToken()));
     event.setTitle(entity.getTitle());
     event.setDescription(entity.getDescription());
     event.setDateTime(entity.getDateTime());

backend/src/main/java/de/fete/adapter/out/persistence/RsvpJpaEntity.java

@@ -0,0 +1,68 @@
+package de.fete.adapter.out.persistence;
+
+import jakarta.persistence.Column;
+import jakarta.persistence.Entity;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.GenerationType;
+import jakarta.persistence.Id;
+import jakarta.persistence.Table;
+import java.util.UUID;
+
+/** JPA entity mapping to the rsvps table. */
+@Entity
+@Table(name = "rsvps")
+public class RsvpJpaEntity {
+
+  @Id
+  @GeneratedValue(strategy = GenerationType.IDENTITY)
+  private Long id;
+
+  @Column(name = "rsvp_token", nullable = false, unique = true)
+  private UUID rsvpToken;
+
+  @Column(name = "event_id", nullable = false)
+  private Long eventId;
+
+  @Column(nullable = false, length = 100)
+  private String name;
+
+  /** Returns the internal database ID. */
+  public Long getId() {
+    return id;
+  }
+
+  /** Sets the internal database ID. */
+  public void setId(Long id) {
+    this.id = id;
+  }
+
+  /** Returns the RSVP token. */
+  public UUID getRsvpToken() {
+    return rsvpToken;
+  }
+
+  /** Sets the RSVP token. */
+  public void setRsvpToken(UUID rsvpToken) {
+    this.rsvpToken = rsvpToken;
+  }
+
+  /** Returns the event ID. */
+  public Long getEventId() {
+    return eventId;
+  }
+
+  /** Sets the event ID. */
+  public void setEventId(Long eventId) {
+    this.eventId = eventId;
+  }
+
+  /** Returns the guest's display name. */
+  public String getName() {
+    return name;
+  }
+
+  /** Sets the guest's display name. */
+  public void setName(String name) {
+    this.name = name;
+  }
+}

backend/src/main/java/de/fete/adapter/out/persistence/RsvpJpaRepository.java

@@ -0,0 +1,14 @@
+package de.fete.adapter.out.persistence;
+
+import java.util.UUID;
+import org.springframework.data.jpa.repository.JpaRepository;
+
+/** Spring Data JPA repository for RSVP entities. */
+public interface RsvpJpaRepository extends JpaRepository<RsvpJpaEntity, Long> {
+
+  /** Finds an RSVP by its token. */
+  java.util.Optional<RsvpJpaEntity> findByRsvpToken(UUID rsvpToken);
+
+  /** Counts RSVPs for the given event. */
+  long countByEventId(Long eventId);
+}

backend/src/main/java/de/fete/adapter/out/persistence/RsvpPersistenceAdapter.java

@@ -0,0 +1,48 @@
+package de.fete.adapter.out.persistence;
+
+import de.fete.domain.model.Rsvp;
+import de.fete.domain.model.RsvpToken;
+import de.fete.domain.port.out.RsvpRepository;
+import org.springframework.stereotype.Repository;
+
+/** Persistence adapter implementing the RsvpRepository outbound port. */
+@Repository
+public class RsvpPersistenceAdapter implements RsvpRepository {
+
+  private final RsvpJpaRepository jpaRepository;
+
+  /** Creates a new adapter with the given JPA repository. */
+  public RsvpPersistenceAdapter(RsvpJpaRepository jpaRepository) {
+    this.jpaRepository = jpaRepository;
+  }
+
+  @Override
+  public Rsvp save(Rsvp rsvp) {
+    RsvpJpaEntity entity = toEntity(rsvp);
+    RsvpJpaEntity saved = jpaRepository.save(entity);
+    return toDomain(saved);
+  }
+
+  @Override
+  public long countByEventId(Long eventId) {
+    return jpaRepository.countByEventId(eventId);
+  }
+
+  private RsvpJpaEntity toEntity(Rsvp rsvp) {
+    var entity = new RsvpJpaEntity();
+    entity.setId(rsvp.getId());
+    entity.setRsvpToken(rsvp.getRsvpToken().value());
+    entity.setEventId(rsvp.getEventId());
+    entity.setName(rsvp.getName());
+    return entity;
+  }
+
+  private Rsvp toDomain(RsvpJpaEntity entity) {
+    var rsvp = new Rsvp();
+    rsvp.setId(entity.getId());
+    rsvp.setRsvpToken(new RsvpToken(entity.getRsvpToken()));
+    rsvp.setEventId(entity.getEventId());
+    rsvp.setName(entity.getName());
+    return rsvp;
+  }
+}

backend/src/main/java/de/fete/application/service/EventExpiredException.java

@@ -0,0 +1,12 @@
+package de.fete.application.service;
+
+import java.util.UUID;
+
+/** Thrown when an RSVP is attempted on an expired event. */
+public class EventExpiredException extends RuntimeException {
+
+  /** Creates a new exception for the given event token. */
+  public EventExpiredException(UUID eventToken) {
+    super("Event has expired: " + eventToken);
+  }
+}

backend/src/main/java/de/fete/application/service/EventService.java

@@ -2,6 +2,8 @@ package de.fete.application.service;
 
 import de.fete.domain.model.CreateEventCommand;
 import de.fete.domain.model.Event;
+import de.fete.domain.model.EventToken;
+import de.fete.domain.model.OrganizerToken;
 import de.fete.domain.port.in.CreateEventUseCase;
 import de.fete.domain.port.in.GetEventUseCase;
 import de.fete.domain.port.out.EventRepository;
@@ -9,7 +11,6 @@ import java.time.Clock;
 import java.time.LocalDate;
 import java.time.OffsetDateTime;
 import java.util.Optional;
-import java.util.UUID;
 import org.springframework.stereotype.Service;
 
 /** Application service implementing event creation and retrieval. */
@@ -32,8 +33,8 @@ public class EventService implements CreateEventUseCase, GetEventUseCase {
     }
 
     var event = new Event();
-    event.setEventToken(UUID.randomUUID());
-    event.setOrganizerToken(UUID.randomUUID());
+    event.setEventToken(EventToken.generate());
+    event.setOrganizerToken(OrganizerToken.generate());
     event.setTitle(command.title());
     event.setDescription(command.description());
     event.setDateTime(command.dateTime());
@@ -46,7 +47,7 @@ public class EventService implements CreateEventUseCase, GetEventUseCase {
   }
 
   @Override
-  public Optional<Event> getByEventToken(UUID eventToken) {
+  public Optional<Event> getByEventToken(EventToken eventToken) {
     return eventRepository.findByEventToken(eventToken);
   }
 }

backend/src/main/java/de/fete/application/service/RsvpService.java

@@ -0,0 +1,43 @@
+package de.fete.application.service;
+
+import de.fete.domain.model.Event;
+import de.fete.domain.model.EventToken;
+import de.fete.domain.model.Rsvp;
+import de.fete.domain.model.RsvpToken;
+import de.fete.domain.port.in.CreateRsvpUseCase;
+import de.fete.domain.port.out.EventRepository;
+import de.fete.domain.port.out.RsvpRepository;
+import java.time.Clock;
+import org.springframework.stereotype.Service;
+
+/** Application service implementing RSVP creation. */
+@Service
+public class RsvpService implements CreateRsvpUseCase {
+
+  private final EventRepository eventRepository;
+  private final RsvpRepository rsvpRepository;
+  private final Clock clock;
+
+  /** Creates a new RsvpService. */
+  public RsvpService(
+      EventRepository eventRepository,
+      RsvpRepository rsvpRepository,
+      Clock clock) {
+    this.eventRepository = eventRepository;
+    this.rsvpRepository = rsvpRepository;
+    this.clock = clock;
+  }
+
+  @Override
+  public Rsvp createRsvp(EventToken eventToken, String name) {
+    Event event = eventRepository.findByEventToken(eventToken)
+        .orElseThrow(() -> new EventNotFoundException(eventToken.value()));
+
+    var rsvp = new Rsvp();
+    rsvp.setRsvpToken(RsvpToken.generate());
+    rsvp.setEventId(event.getId());
+    rsvp.setName(name.strip());
+
+    return rsvpRepository.save(rsvp);
+  }
+}

backend/src/main/java/de/fete/domain/model/Event.java

@@ -3,14 +3,13 @@ package de.fete.domain.model;
 import java.time.LocalDate;
 import java.time.OffsetDateTime;
 import java.time.ZoneId;
-import java.util.UUID;
 
 /** Domain entity representing an event. */
 public class Event {
 
   private Long id;
-  private UUID eventToken;
-  private UUID organizerToken;
+  private EventToken eventToken;
+  private OrganizerToken organizerToken;
   private String title;
   private String description;
   private OffsetDateTime dateTime;
@@ -29,23 +28,23 @@ public class Event {
     this.id = id;
   }
 
-  /** Returns the public event token (UUID). */
-  public UUID getEventToken() {
+  /** Returns the public event token. */
+  public EventToken getEventToken() {
     return eventToken;
   }
 
   /** Sets the public event token. */
-  public void setEventToken(UUID eventToken) {
+  public void setEventToken(EventToken eventToken) {
     this.eventToken = eventToken;
   }
 
-  /** Returns the secret organizer token (UUID). */
-  public UUID getOrganizerToken() {
+  /** Returns the secret organizer token. */
+  public OrganizerToken getOrganizerToken() {
     return organizerToken;
   }
 
   /** Sets the secret organizer token. */
-  public void setOrganizerToken(UUID organizerToken) {
+  public void setOrganizerToken(OrganizerToken organizerToken) {
     this.organizerToken = organizerToken;
   }
 

backend/src/main/java/de/fete/domain/model/EventToken.java

@@ -0,0 +1,18 @@
+package de.fete.domain.model;
+
+import java.util.Objects;
+import java.util.UUID;
+
+/** Type-safe wrapper for the public event token. */
+public record EventToken(UUID value) {
+
+  /** Validates that the token value is not null. */
+  public EventToken {
+    Objects.requireNonNull(value, "eventToken must not be null");
+  }
+
+  /** Generates a new random event token. */
+  public static EventToken generate() {
+    return new EventToken(UUID.randomUUID());
+  }
+}

backend/src/main/java/de/fete/domain/model/OrganizerToken.java

@@ -0,0 +1,18 @@
+package de.fete.domain.model;
+
+import java.util.Objects;
+import java.util.UUID;
+
+/** Type-safe wrapper for the secret organizer token. */
+public record OrganizerToken(UUID value) {
+
+  /** Validates that the token value is not null. */
+  public OrganizerToken {
+    Objects.requireNonNull(value, "organizerToken must not be null");
+  }
+
+  /** Generates a new random organizer token. */
+  public static OrganizerToken generate() {
+    return new OrganizerToken(UUID.randomUUID());
+  }
+}

backend/src/main/java/de/fete/domain/model/Rsvp.java

@@ -0,0 +1,50 @@
+package de.fete.domain.model;
+
+/** Domain entity representing an RSVP. */
+public class Rsvp {
+
+  private Long id;
+  private RsvpToken rsvpToken;
+  private Long eventId;
+  private String name;
+
+  /** Returns the internal database ID. */
+  public Long getId() {
+    return id;
+  }
+
+  /** Sets the internal database ID. */
+  public void setId(Long id) {
+    this.id = id;
+  }
+
+  /** Returns the RSVP token. */
+  public RsvpToken getRsvpToken() {
+    return rsvpToken;
+  }
+
+  /** Sets the RSVP token. */
+  public void setRsvpToken(RsvpToken rsvpToken) {
+    this.rsvpToken = rsvpToken;
+  }
+
+  /** Returns the event ID this RSVP belongs to. */
+  public Long getEventId() {
+    return eventId;
+  }
+
+  /** Sets the event ID. */
+  public void setEventId(Long eventId) {
+    this.eventId = eventId;
+  }
+
+  /** Returns the guest's display name. */
+  public String getName() {
+    return name;
+  }
+
+  /** Sets the guest's display name. */
+  public void setName(String name) {
+    this.name = name;
+  }
+}

backend/src/main/java/de/fete/domain/model/RsvpToken.java

@@ -0,0 +1,18 @@
+package de.fete.domain.model;
+
+import java.util.Objects;
+import java.util.UUID;
+
+/** Type-safe wrapper for the RSVP token. */
+public record RsvpToken(UUID value) {
+
+  /** Validates that the token value is not null. */
+  public RsvpToken {
+    Objects.requireNonNull(value, "rsvpToken must not be null");
+  }
+
+  /** Generates a new random RSVP token. */
+  public static RsvpToken generate() {
+    return new RsvpToken(UUID.randomUUID());
+  }
+}

backend/src/main/java/de/fete/domain/port/in/CreateRsvpUseCase.java

@@ -0,0 +1,11 @@
+package de.fete.domain.port.in;
+
+import de.fete.domain.model.EventToken;
+import de.fete.domain.model.Rsvp;
+
+/** Inbound port for creating a new RSVP. */
+public interface CreateRsvpUseCase {
+
+  /** Creates an RSVP for the given event and guest name. */
+  Rsvp createRsvp(EventToken eventToken, String name);
+}

backend/src/main/java/de/fete/domain/port/in/GetEventUseCase.java

@@ -1,12 +1,12 @@
 package de.fete.domain.port.in;
 
 import de.fete.domain.model.Event;
+import de.fete.domain.model.EventToken;
 import java.util.Optional;
-import java.util.UUID;
 
 /** Inbound port for retrieving a public event by its token. */
 public interface GetEventUseCase {
 
   /** Finds an event by its public event token. */
-  Optional<Event> getByEventToken(UUID eventToken);
+  Optional<Event> getByEventToken(EventToken eventToken);
 }

backend/src/main/java/de/fete/domain/port/out/EventRepository.java

@@ -1,8 +1,8 @@
 package de.fete.domain.port.out;
 
 import de.fete.domain.model.Event;
+import de.fete.domain.model.EventToken;
 import java.util.Optional;
-import java.util.UUID;
 
 /** Outbound port for persisting and retrieving events. */
 public interface EventRepository {
@@ -11,5 +11,5 @@ public interface EventRepository {
   Event save(Event event);
 
   /** Finds an event by its public event token. */
-  Optional<Event> findByEventToken(UUID eventToken);
+  Optional<Event> findByEventToken(EventToken eventToken);
 }

backend/src/main/java/de/fete/domain/port/out/RsvpRepository.java

@@ -0,0 +1,13 @@
+package de.fete.domain.port.out;
+
+import de.fete.domain.model.Rsvp;
+
+/** Outbound port for persisting and querying RSVPs. */
+public interface RsvpRepository {
+
+  /** Persists the given RSVP and returns it with generated fields populated. */
+  Rsvp save(Rsvp rsvp);
+
+  /** Counts the number of RSVPs for the given event. */
+  long countByEventId(Long eventId);
+}

backend/src/main/resources/db/changelog/003-create-rsvps-table.xml

@@ -0,0 +1,36 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<databaseChangeLog
+    xmlns="http://www.liquibase.org/xml/ns/dbchangelog"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog
+        http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-latest.xsd">
+
+    <changeSet id="003-create-rsvps-table" author="fete">
+        <createTable tableName="rsvps">
+            <column name="id" type="bigserial" autoIncrement="true">
+                <constraints primaryKey="true" nullable="false"/>
+            </column>
+            <column name="rsvp_token" type="uuid">
+                <constraints nullable="false" unique="true"/>
+            </column>
+            <column name="event_id" type="bigint">
+                <constraints nullable="false"
+                             foreignKeyName="fk_rsvps_event_id"
+                             references="events(id)"
+                             deleteCascade="true"/>
+            </column>
+            <column name="name" type="varchar(100)">
+                <constraints nullable="false"/>
+            </column>
+        </createTable>
+
+        <createIndex tableName="rsvps" indexName="idx_rsvps_event_id">
+            <column name="event_id"/>
+        </createIndex>
+
+        <createIndex tableName="rsvps" indexName="idx_rsvps_rsvp_token">
+            <column name="rsvp_token"/>
+        </createIndex>
+    </changeSet>
+
+</databaseChangeLog>

backend/src/main/resources/db/changelog/db.changelog-master.xml

@@ -8,5 +8,6 @@
     <include file="db/changelog/000-baseline.xml"/>
     <include file="db/changelog/001-create-events-table.xml"/>
     <include file="db/changelog/002-add-timezone-column.xml"/>
+    <include file="db/changelog/003-create-rsvps-table.xml"/>
 
 </databaseChangeLog>

backend/src/main/resources/openapi/api.yaml

@@ -37,6 +37,52 @@ paths:
               schema:
                 $ref: "#/components/schemas/ValidationProblemDetail"
 
+  /events/{token}/rsvps:
+    post:
+      operationId: createRsvp
+      summary: Submit an RSVP for an event
+      tags:
+        - events
+      parameters:
+        - name: token
+          in: path
+          required: true
+          schema:
+            type: string
+            format: uuid
+          description: Public event token
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/CreateRsvpRequest"
+      responses:
+        "201":
+          description: RSVP created successfully
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/CreateRsvpResponse"
+        "400":
+          description: Validation failed (e.g. blank name)
+          content:
+            application/problem+json:
+              schema:
+                $ref: "#/components/schemas/ValidationProblemDetail"
+        "404":
+          description: Event not found
+          content:
+            application/problem+json:
+              schema:
+                $ref: "#/components/schemas/ProblemDetail"
+        "409":
+          description: Event has expired — RSVPs no longer accepted
+          content:
+            application/problem+json:
+              schema:
+                $ref: "#/components/schemas/ProblemDetail"
+
   /events/{token}:
     get:
       operationId: getEvent
@@ -182,6 +228,34 @@ components:
           description: Whether the event's expiry date has passed
           example: false
 
+    CreateRsvpRequest:
+      type: object
+      required:
+        - name
+      properties:
+        name:
+          type: string
+          minLength: 1
+          maxLength: 100
+          description: Guest's display name
+          example: "Max Mustermann"
+
+    CreateRsvpResponse:
+      type: object
+      required:
+        - rsvpToken
+        - name
+      properties:
+        rsvpToken:
+          type: string
+          format: uuid
+          description: Token identifying this RSVP (store client-side for future updates)
+          example: "d4e5f6a7-b8c9-0123-4567-890abcdef012"
+        name:
+          type: string
+          description: Guest's display name as stored
+          example: "Max Mustermann"
+
     ProblemDetail:
       type: object
       properties:

backend/src/test/java/de/fete/adapter/in/web/EventControllerIntegrationTest.java

@@ -11,8 +11,12 @@ import com.fasterxml.jackson.databind.ObjectMapper;
 import de.fete.TestcontainersConfig;
 import de.fete.adapter.in.web.model.CreateEventRequest;
 import de.fete.adapter.in.web.model.CreateEventResponse;
+import de.fete.adapter.in.web.model.CreateRsvpRequest;
+import de.fete.adapter.in.web.model.CreateRsvpResponse;
 import de.fete.adapter.out.persistence.EventJpaEntity;
 import de.fete.adapter.out.persistence.EventJpaRepository;
+import de.fete.adapter.out.persistence.RsvpJpaEntity;
+import de.fete.adapter.out.persistence.RsvpJpaRepository;
 import java.time.LocalDate;
 import java.time.OffsetDateTime;
 import java.time.ZoneOffset;
@@ -39,6 +43,9 @@ class EventControllerIntegrationTest {
   @Autowired
   private EventJpaRepository jpaRepository;
 
+  @Autowired
+  private RsvpJpaRepository rsvpJpaRepository;
+
   // --- Create Event tests ---
 
   @Test
@@ -268,6 +275,80 @@ class EventControllerIntegrationTest {
         .andExpect(jsonPath("$.expired").value(true));
   }
 
+  // --- RSVP tests ---
+
+  @Test
+  void createRsvpReturns201WithToken() throws Exception {
+    EventJpaEntity event = seedEvent(
+        "RSVP Event", "Join us!", "Europe/Berlin",
+        "Berlin", LocalDate.now().plusDays(30));
+
+    var request = new CreateRsvpRequest().name("Max Mustermann");
+
+    var result = mockMvc.perform(post("/api/events/" + event.getEventToken() + "/rsvps")
+            .contentType(MediaType.APPLICATION_JSON)
+            .content(objectMapper.writeValueAsString(request)))
+        .andExpect(status().isCreated())
+        .andExpect(jsonPath("$.rsvpToken").isNotEmpty())
+        .andExpect(jsonPath("$.name").value("Max Mustermann"))
+        .andReturn();
+
+    var response = objectMapper.readValue(
+        result.getResponse().getContentAsString(), CreateRsvpResponse.class);
+
+    RsvpJpaEntity persisted = rsvpJpaRepository
+        .findByRsvpToken(response.getRsvpToken()).orElseThrow();
+    assertThat(persisted.getName()).isEqualTo("Max Mustermann");
+    assertThat(persisted.getEventId()).isEqualTo(event.getId());
+  }
+
+  @Test
+  void createRsvpWithBlankNameReturns400() throws Exception {
+    EventJpaEntity event = seedEvent(
+        "RSVP Event", null, "Europe/Berlin",
+        null, LocalDate.now().plusDays(30));
+
+    var request = new CreateRsvpRequest().name("");
+
+    mockMvc.perform(post("/api/events/" + event.getEventToken() + "/rsvps")
+            .contentType(MediaType.APPLICATION_JSON)
+            .content(objectMapper.writeValueAsString(request)))
+        .andExpect(status().isBadRequest())
+        .andExpect(content().contentTypeCompatibleWith("application/problem+json"));
+  }
+
+  @Test
+  void attendeeCountIncreasesAfterRsvp() throws Exception {
+    EventJpaEntity event = seedEvent(
+        "Count Event", null, "Europe/Berlin",
+        null, LocalDate.now().plusDays(30));
+
+    mockMvc.perform(get("/api/events/" + event.getEventToken()))
+        .andExpect(jsonPath("$.attendeeCount").value(0));
+
+    var request = new CreateRsvpRequest().name("First Guest");
+
+    mockMvc.perform(post("/api/events/" + event.getEventToken() + "/rsvps")
+            .contentType(MediaType.APPLICATION_JSON)
+            .content(objectMapper.writeValueAsString(request)))
+        .andExpect(status().isCreated());
+
+    mockMvc.perform(get("/api/events/" + event.getEventToken()))
+        .andExpect(jsonPath("$.attendeeCount").value(1));
+  }
+
+  @Test
+  void createRsvpForUnknownEventReturns404() throws Exception {
+    var request = new CreateRsvpRequest().name("Ghost");
+
+    mockMvc.perform(post("/api/events/" + UUID.randomUUID() + "/rsvps")
+            .contentType(MediaType.APPLICATION_JSON)
+            .content(objectMapper.writeValueAsString(request)))
+        .andExpect(status().isNotFound())
+        .andExpect(content().contentTypeCompatibleWith("application/problem+json"))
+        .andExpect(jsonPath("$.type").value("urn:problem-type:event-not-found"));
+  }
+
   private EventJpaEntity seedEvent(
       String title, String description, String timezone,
       String location, LocalDate expiryDate) {

backend/src/test/java/de/fete/adapter/out/persistence/EventPersistenceAdapterTest.java

@@ -4,13 +4,14 @@ import static org.assertj.core.api.Assertions.assertThat;
 
 import de.fete.TestcontainersConfig;
 import de.fete.domain.model.Event;
+import de.fete.domain.model.EventToken;
+import de.fete.domain.model.OrganizerToken;
 import de.fete.domain.port.out.EventRepository;
 import java.time.LocalDate;
 import java.time.OffsetDateTime;
 import java.time.ZoneId;
 import java.time.ZoneOffset;
 import java.util.Optional;
-import java.util.UUID;
 import org.junit.jupiter.api.Test;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
@@ -47,7 +48,7 @@ class EventPersistenceAdapterTest {
 
   @Test
   void findByUnknownEventTokenReturnsEmpty() {
-    Optional<Event> found = eventRepository.findByEventToken(UUID.randomUUID());
+    Optional<Event> found = eventRepository.findByEventToken(EventToken.generate());
 
     assertThat(found).isEmpty();
   }
@@ -61,8 +62,8 @@ class EventPersistenceAdapterTest {
         OffsetDateTime.of(2026, 3, 4, 12, 0, 0, 0, ZoneOffset.UTC);
 
     var event = new Event();
-    event.setEventToken(UUID.randomUUID());
-    event.setOrganizerToken(UUID.randomUUID());
+    event.setEventToken(EventToken.generate());
+    event.setOrganizerToken(OrganizerToken.generate());
     event.setTitle("Full Event");
     event.setDescription("A detailed description");
     event.setDateTime(dateTime);
@@ -87,8 +88,8 @@ class EventPersistenceAdapterTest {
 
   private Event buildEvent() {
     var event = new Event();
-    event.setEventToken(UUID.randomUUID());
-    event.setOrganizerToken(UUID.randomUUID());
+    event.setEventToken(EventToken.generate());
+    event.setOrganizerToken(OrganizerToken.generate());
     event.setTitle("Test Event");
     event.setDescription("Test description");
     event.setDateTime(OffsetDateTime.now().plusDays(7));

backend/src/test/java/de/fete/application/service/EventServiceTest.java

@@ -9,6 +9,7 @@ import static org.mockito.Mockito.when;
 
 import de.fete.domain.model.CreateEventCommand;
 import de.fete.domain.model.Event;
+import de.fete.domain.model.EventToken;
 import de.fete.domain.port.out.EventRepository;
 import java.time.Clock;
 import java.time.Instant;
@@ -17,7 +18,6 @@ import java.time.OffsetDateTime;
 import java.time.ZoneId;
 import java.time.ZoneOffset;
 import java.util.Optional;
-import java.util.UUID;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
@@ -130,7 +130,7 @@ class EventServiceTest {
 
   @Test
   void getByEventTokenReturnsEvent() {
-    UUID token = UUID.randomUUID();
+    EventToken token = EventToken.generate();
     var event = new Event();
     event.setEventToken(token);
     event.setTitle("Found Event");
@@ -145,7 +145,7 @@ class EventServiceTest {
 
   @Test
   void getByEventTokenReturnsEmptyForUnknownToken() {
-    UUID token = UUID.randomUUID();
+    EventToken token = EventToken.generate();
     when(eventRepository.findByEventToken(token))
         .thenReturn(Optional.empty());
 

backend/src/test/java/de/fete/application/service/RsvpServiceTest.java

@@ -0,0 +1,115 @@
+package de.fete.application.service;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import de.fete.domain.model.Event;
+import de.fete.domain.model.EventToken;
+import de.fete.domain.model.OrganizerToken;
+import de.fete.domain.model.Rsvp;
+import de.fete.domain.port.out.EventRepository;
+import de.fete.domain.port.out.RsvpRepository;
+import java.time.Clock;
+import java.time.Instant;
+import java.time.LocalDate;
+import java.time.OffsetDateTime;
+import java.time.ZoneId;
+import java.time.ZoneOffset;
+import java.util.Optional;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.ArgumentCaptor;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+@ExtendWith(MockitoExtension.class)
+class RsvpServiceTest {
+
+  private static final ZoneId ZONE = ZoneId.of("Europe/Berlin");
+  private static final Instant FIXED_INSTANT =
+      LocalDate.of(2026, 3, 5).atStartOfDay(ZONE).toInstant();
+  private static final Clock FIXED_CLOCK = Clock.fixed(FIXED_INSTANT, ZONE);
+
+  @Mock
+  private EventRepository eventRepository;
+
+  @Mock
+  private RsvpRepository rsvpRepository;
+
+  private RsvpService rsvpService;
+
+  @BeforeEach
+  void setUp() {
+    rsvpService = new RsvpService(eventRepository, rsvpRepository, FIXED_CLOCK);
+  }
+
+  @Test
+  void createRsvpSucceedsForActiveEvent() {
+    Event event = buildActiveEvent();
+    EventToken token = event.getEventToken();
+    when(eventRepository.findByEventToken(token)).thenReturn(Optional.of(event));
+    when(rsvpRepository.save(any(Rsvp.class)))
+        .thenAnswer(invocation -> invocation.getArgument(0));
+
+    Rsvp result = rsvpService.createRsvp(token, "Max Mustermann");
+
+    assertThat(result.getName()).isEqualTo("Max Mustermann");
+    assertThat(result.getRsvpToken()).isNotNull();
+    assertThat(result.getEventId()).isEqualTo(event.getId());
+  }
+
+  @Test
+  void createRsvpPersistsViaRepository() {
+    Event event = buildActiveEvent();
+    EventToken token = event.getEventToken();
+    when(eventRepository.findByEventToken(token)).thenReturn(Optional.of(event));
+    when(rsvpRepository.save(any(Rsvp.class)))
+        .thenAnswer(invocation -> invocation.getArgument(0));
+
+    rsvpService.createRsvp(token, "Test Guest");
+
+    ArgumentCaptor<Rsvp> captor = ArgumentCaptor.forClass(Rsvp.class);
+    verify(rsvpRepository).save(captor.capture());
+    assertThat(captor.getValue().getName()).isEqualTo("Test Guest");
+    assertThat(captor.getValue().getEventId()).isEqualTo(event.getId());
+  }
+
+  @Test
+  void createRsvpThrowsWhenEventNotFound() {
+    EventToken token = EventToken.generate();
+    when(eventRepository.findByEventToken(token)).thenReturn(Optional.empty());
+
+    assertThatThrownBy(() -> rsvpService.createRsvp(token, "Guest"))
+        .isInstanceOf(EventNotFoundException.class);
+  }
+
+  @Test
+  void createRsvpTrimsName() {
+    Event event = buildActiveEvent();
+    EventToken token = event.getEventToken();
+    when(eventRepository.findByEventToken(token)).thenReturn(Optional.of(event));
+    when(rsvpRepository.save(any(Rsvp.class)))
+        .thenAnswer(invocation -> invocation.getArgument(0));
+
+    Rsvp result = rsvpService.createRsvp(token, "  Max  ");
+
+    assertThat(result.getName()).isEqualTo("Max");
+  }
+
+  private Event buildActiveEvent() {
+    var event = new Event();
+    event.setId(1L);
+    event.setEventToken(EventToken.generate());
+    event.setOrganizerToken(OrganizerToken.generate());
+    event.setTitle("Test Event");
+    event.setDateTime(OffsetDateTime.of(2026, 6, 15, 20, 0, 0, 0, ZoneOffset.ofHours(2)));
+    event.setTimezone(ZONE);
+    event.setExpiryDate(LocalDate.of(2026, 7, 15));
+    event.setCreatedAt(OffsetDateTime.now(FIXED_CLOCK));
+    return event;
+  }
+}