diff --git a/build.gradle.kts b/build.gradle.kts
index f42cd89..2ff669d 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -11,8 +11,6 @@ spotless {
         target("**/src/**/java/**/*.java")
         removeUnusedImports()
         importOrder()
-        //cleanthat()
-        clangFormat("18.1.8").style("file:config/clang-format")
         licenseHeader("/* © SRSoftware 2024 */")
         toggleOffOn()
     }
diff --git a/de.srsoftware.cal.api/src/main/java/de/srsoftware/cal/api/Appointment.java b/de.srsoftware.cal.api/src/main/java/de/srsoftware/cal/api/Appointment.java
index d31dd1f..424078b 100644
--- a/de.srsoftware.cal.api/src/main/java/de/srsoftware/cal/api/Appointment.java
+++ b/de.srsoftware.cal.api/src/main/java/de/srsoftware/cal/api/Appointment.java
@@ -30,21 +30,18 @@ public interface Appointment {
 	 */
 	String description();
 
-
 	/**
 	 * The date and time when the appointment is scheduled to end
 	 * @return an optionals LocalDateTime
 	 */
 	Optional<LocalDateTime> end();
 
-
 	/**
 	 * represent this event as ical entry
 	 * @return the ical string
 	 */
 	String ical();
 
-
 	/**
 	 * ID of the appointment – unique within this system
 	 * @return the appointment`s id
@@ -75,14 +72,12 @@ public interface Appointment {
 	 */
 	LocalDateTime start();
 
-
 	/**
 	 * tags i.e. keywords may be used to filter appointments
 	 * @return the set of tags associated with the current appointment
 	 */
 	Set<String> tags();
 
-
 	/**
 	 * the title of the appointment
 	 * @return the title
diff --git a/de.srsoftware.cal.app/src/main/java/de/srsoftware/cal/app/Application.java b/de.srsoftware.cal.app/src/main/java/de/srsoftware/cal/app/Application.java
index 92abf54..af8fc92 100644
--- a/de.srsoftware.cal.app/src/main/java/de/srsoftware/cal/app/Application.java
+++ b/de.srsoftware.cal.app/src/main/java/de/srsoftware/cal/app/Application.java
@@ -60,7 +60,6 @@ public class Application {
 
 		server.start();
 		// TODO: schedule imports
-		// TODO: update URL, when tags are selected
 		// TODO: allow list start time as URL param
 		// TODO: provide ICAL and WEBDAV links
 	}
diff --git a/de.srsoftware.cal.base/src/main/java/de/srsoftware/cal/BaseAppointment.java b/de.srsoftware.cal.base/src/main/java/de/srsoftware/cal/BaseAppointment.java
index d3cfa0d..602626b 100644
--- a/de.srsoftware.cal.base/src/main/java/de/srsoftware/cal/BaseAppointment.java
+++ b/de.srsoftware.cal.base/src/main/java/de/srsoftware/cal/BaseAppointment.java
@@ -124,7 +124,7 @@ public class BaseAppointment implements Appointment {
 	}
 
 	@Override
-	public String ical() {
+	public String ical() { // TODO: implement
 		return "converting event (%s) to ical not implemented".formatted(title);
 	}
 
@@ -199,4 +199,4 @@ public class BaseAppointment implements Appointment {
 	public Set<Link> links() {
 		return links;
 	}
-}
\ No newline at end of file
+}
diff --git a/de.srsoftware.cal.base/src/main/java/de/srsoftware/cal/BaseImporter.java b/de.srsoftware.cal.base/src/main/java/de/srsoftware/cal/BaseImporter.java
index 89c8183..8937b82 100644
--- a/de.srsoftware.cal.base/src/main/java/de/srsoftware/cal/BaseImporter.java
+++ b/de.srsoftware.cal.base/src/main/java/de/srsoftware/cal/BaseImporter.java
@@ -58,7 +58,6 @@ public abstract class BaseImporter implements Importer {
 		return extractDescriptionTag(eventTag);
 	}
 
-
 	protected Result<String> extractDescription(Tag eventTag) {
 		Result<Tag> titleTag = extractDescriptionTag(eventTag);
 		if (titleTag.optional().isEmpty()) return transform(titleTag);
@@ -73,7 +72,6 @@ public abstract class BaseImporter implements Importer {
 		return error("not implemented");
 	}
 
-
 	protected Result<LocalDateTime> extractEnd(Tag eventTag) {
 		Result<Tag> endTag = extractEndTag(eventTag);
 		if (endTag.optional().isEmpty()) return transform(endTag);
@@ -114,79 +112,75 @@ public abstract class BaseImporter implements Importer {
 		return Payload.of(event);
 	}
 
-
 	private Result<Appointment> extractEvent(Result<Tag> domResult, Link eventPage) {
 		return switch (domResult) {
-			case Payload<Tag> payload -> extractEvent(payload.get(), eventPage);
-			case Error<Tag> err -> err.transform();
-			default -> invalidParameter(domResult);
-		};
-	}
-
-	protected abstract Result<Tag> extractEventTag(Result<Tag> pageResult);
-
-	protected abstract Result<List<String>> extractEventUrls(Result<Tag> programPage);
-
-
-	protected List<Link> extractLinks(Tag appointmentTag) {
-		var links = new ArrayList<Link>();
-
-		extractLinksTag(appointmentTag) //
-				.map(this::extractLinkAnchors)
-				.optional()
-				.stream()
-				.flatMap(List::stream).forEach(anchor -> {
-			var href = anchor.get("href");
-			if (href == null) return;
-			if (!href.contains("://")) href = baseUrl() + href;
-			var text = anchor.inner(0).orElse(href);
-			Payload //
-					.of(href)
-					.map(BaseImporter::url)
-					.map(url -> link(url,text))
-					.optional()
-					.ifPresent(links::add);
-		});
-		return links;
-	}
-
-	public abstract Result<List<Tag>> extractLinkAnchors(Result<Tag> tagResult);
-
-	protected Result<Tag> extractLinksTag(Tag eventTag) {
-		return extractDescriptionTag(eventTag);
-	}
-
-	protected Result<String> extractLocation(Tag eventTag) {
-		Result<Tag> locationTag = extractLocationTag(eventTag);
-		if (locationTag.optional().isEmpty()) return transform(locationTag);
-		return Payload.of(locationTag.optional().get().toString(2));
-	}
-
-	protected abstract Result<Tag> extractLocationTag(Tag eventTag);
-
-
-	protected Result<LocalDateTime> extractStart(Tag eventTag) {
-		Result<Tag> startTag = extractStartTag(eventTag);
-		if (startTag.optional().isEmpty()) return transform(startTag);
-		return parseStartDate(startTag.optional().get().strip());
-	}
-
-	protected abstract Result<Tag> extractStartTag(Tag eventTag);
-
-
-	protected abstract List<String> extractTags(Tag eventTag);
-
-	protected Result<String> extractTitle(Tag eventTag) {
-		Result<Tag> titleTag = extractTitleTag(eventTag);
-		if (titleTag.optional().isEmpty()) return transform(titleTag);
-		var inner = titleTag.optional().flatMap(tag -> tag.inner(2));
-		return inner.isPresent() ? Payload.of(inner.get()) :
-				error("No title found");
+            case Payload<Tag> payload -> extractEvent(payload.get(), eventPage);
+            case Error<Tag> err -> err.transform();
+            default -> invalidParameter(domResult);
+        };
+    }
+
+    protected abstract Result<Tag> extractEventTag(Result<Tag> pageResult);
+
+    protected abstract Result<List<String>> extractEventUrls(Result<Tag> programPage);
+
+    protected List<Link> extractLinks(Tag appointmentTag) {
+        var links = new ArrayList<Link>();
+
+        extractLinksTag(appointmentTag) //
+                .map(this::extractLinkAnchors)
+                .optional()
+                .stream()
+                .flatMap(List::stream)
+                .forEach(anchor -> {
+                    var href = anchor.get("href");
+                    if (href == null) return;
+                    if (!href.contains("://")) href = baseUrl() + href;
+                    var text = anchor.inner(0).orElse(href);
+                    Payload //
+                            .of(href)
+                            .map(BaseImporter::url)
+                            .map(url -> link(url, text))
+                            .optional()
+                            .ifPresent(links::add);
+                });
+        return links;
+    }
+
+    public abstract Result<List<Tag>> extractLinkAnchors(Result<Tag> tagResult);
+
+    protected Result<Tag> extractLinksTag(Tag eventTag) {
+        return extractDescriptionTag(eventTag);
+    }
+
+    protected Result<String> extractLocation(Tag eventTag) {
+        Result<Tag> locationTag = extractLocationTag(eventTag);
+        if (locationTag.optional().isEmpty()) return transform(locationTag);
+        return Payload.of(locationTag.optional().get().toString(2));
+    }
+
+    protected abstract Result<Tag> extractLocationTag(Tag eventTag);
+
+    protected Result<LocalDateTime> extractStart(Tag eventTag) {
+        Result<Tag> startTag = extractStartTag(eventTag);
+        if (startTag.optional().isEmpty()) return transform(startTag);
+        return parseStartDate(startTag.optional().get().strip());
+    }
+
+    protected abstract Result<Tag> extractStartTag(Tag eventTag);
+
+    protected abstract List<String> extractTags(Tag eventTag);
+
+    protected Result<String> extractTitle(Tag eventTag) {
+        Result<Tag> titleTag = extractTitleTag(eventTag);
+        if (titleTag.optional().isEmpty()) return transform(titleTag);
+        var inner = titleTag.optional().flatMap(tag -> tag.inner(2));
+        return inner.isPresent() ? Payload.of(inner.get()) :
+	            error("No title found");
 		}
 
 		protected abstract Result<Tag> extractTitleTag(Tag eventTag);
 
-
 		@Override
 		public Stream<Appointment> fetch() {
 			var	       url    = Payload.of(programURL());
@@ -249,24 +243,24 @@ public abstract class BaseImporter implements Importer {
 
 		protected Result<Tag> parseXML(Result<InputStream> inputStream) {
 			return switch (inputStream) {
-			case Payload<InputStream> payload -> XMLParser.parse(payload.get());
-			case Error<InputStream> error -> error.transform();
-			default -> invalidParameter(inputStream);
-		};
-	}
-
-	protected Result<InputStream> preload(Result<InputStream> inputStream) {
-		switch (inputStream) {
-			case Payload<InputStream> payload:
-				try {
-					return Payload.of(XMLParser.preload(payload.get()));
-				} catch (IOException e) {
-					return error(e, "Failed to buffer data from %s", payload);
-				}
-			case Error<InputStream> error:
-				return error.transform();
-			default:
-				return invalidParameter(inputStream);
+            case Payload<InputStream> payload -> XMLParser.parse(payload.get());
+            case Error<InputStream> error -> error.transform();
+            default -> invalidParameter(inputStream);
+        };
+    }
+
+    protected Result<InputStream> preload(Result<InputStream> inputStream) {
+        switch (inputStream) {
+            case Payload<InputStream> payload:
+	            try {
+		            return Payload.of(XMLParser.preload(payload.get()));
+	            } catch (IOException e) {
+		            return error(e, "Failed to buffer data from %s", payload);
+	            }
+            case Error<InputStream> error:
+	            return error.transform();
+            default:
+	            return invalidParameter(inputStream);
 			}
 		}
 
@@ -284,7 +278,6 @@ public abstract class BaseImporter implements Importer {
 			}
 		}
 
-
 		protected static Result<Integer> toNumericMonth(String month) {
 			month = month.toLowerCase();
 			if (month.startsWith("ja")) return Payload.of(1);
@@ -302,7 +295,6 @@ public abstract class BaseImporter implements Importer {
 			return error("Failed to recognize \"%s\" as a month!", month);
 		}
 
-
 		protected static Result<URL> url(Result<String> urlResult) {
 			if (urlResult.optional().isEmpty()) return transform(urlResult);
 			var url = urlResult.optional().get();
diff --git a/de.srsoftware.cal.db/src/main/java/de/srsoftware/cal/db/Database.java b/de.srsoftware.cal.db/src/main/java/de/srsoftware/cal/db/Database.java
index b15a462..f4a1c0f 100644
--- a/de.srsoftware.cal.db/src/main/java/de/srsoftware/cal/db/Database.java
+++ b/de.srsoftware.cal.db/src/main/java/de/srsoftware/cal/db/Database.java
@@ -16,7 +16,7 @@ public interface Database {
 	 * @param appointment the appointment to store
 	 * @return a clone of the provided appointment with id field set
 	 */
-	public Result<Appointment> add(Appointment appointment);
+	Result<Appointment> add(Appointment appointment);
 
 	Result<List<String>> findTags(String infix);
 
@@ -28,7 +28,7 @@ public interface Database {
 	 * @param till restrict appointments to times before this date time
 	 * @return list of appointments in this time span
 	 */
-	public Result<List<Appointment>> list(LocalDateTime from, LocalDateTime till, Integer count, Integer offset);
+	Result<List<Appointment>> list(LocalDateTime from, LocalDateTime till, Integer count, Integer offset);
 
 	/**
 	 * list appointments
@@ -37,7 +37,7 @@ public interface Database {
 	 * @param offset the number of appointments to skip
 	 * @return the list of appointments fetched from the db
 	 */
-	public List<Appointment> listByTags(Set<String> tags, Integer count, Integer offset);
+	List<Appointment> listByTags(Set<String> tags, Integer count, Integer offset);
 
 	Result<Appointment> loadEvent(long id);
 
diff --git a/de.srsoftware.cal.db/src/main/java/de/srsoftware/cal/db/MariaDB.java b/de.srsoftware.cal.db/src/main/java/de/srsoftware/cal/db/MariaDB.java
index 74de756..dcd4592 100644
--- a/de.srsoftware.cal.db/src/main/java/de/srsoftware/cal/db/MariaDB.java
+++ b/de.srsoftware.cal.db/src/main/java/de/srsoftware/cal/db/MariaDB.java
@@ -58,7 +58,6 @@ public class MariaDB implements Database {
 		throw new RuntimeException("%s.createTables() not implemented!");
 	}
 
-
 	@Override
 	public Result<Appointment> add(Appointment appointment) {
 		try {
@@ -290,7 +289,6 @@ public class MariaDB implements Database {
 		return Payload.of(appointment);
 	}
 
-
 	@Override
 	public List<Appointment> listByTags(Set<String> tags, Integer count, Integer offset) {
 		return List.of();
diff --git a/de.srsoftware.cal.db/src/main/java/de/srsoftware/cal/db/NotFound.java b/de.srsoftware.cal.db/src/main/java/de/srsoftware/cal/db/NotFound.java
index 25646cf..52ff210 100644
--- a/de.srsoftware.cal.db/src/main/java/de/srsoftware/cal/db/NotFound.java
+++ b/de.srsoftware.cal.db/src/main/java/de/srsoftware/cal/db/NotFound.java
@@ -14,7 +14,6 @@ public class NotFound<None> extends Error<None> {
 		return new NotFound<>(message.formatted(fills), null, null);
 	}
 
-
 	@Override
 	public <NewType> NotFound<NewType> transform() {
 		return new NotFound<>(message(), data(), exceptions());
diff --git a/de.srsoftware.cal.web/src/main/java/de/srsoftware/cal/ApiEndpoint.java b/de.srsoftware.cal.web/src/main/java/de/srsoftware/cal/ApiEndpoint.java
index a87af7d..80aa0a3 100644
--- a/de.srsoftware.cal.web/src/main/java/de/srsoftware/cal/ApiEndpoint.java
+++ b/de.srsoftware.cal.web/src/main/java/de/srsoftware/cal/ApiEndpoint.java
@@ -51,8 +51,8 @@ public class ApiEndpoint extends PathHandler {
 			if (opt.isEmpty()) return transform(res);
 			var event = opt.get();
 			var title = getHeader(ex, TITLE);
-			if (title.isEmpty()) return error("Missing title header");
-			if (!title.get().equals(event.title())) return error("Title mismatch!");
+			if (title.isEmpty()) return HttpError.of(400,"Missing title header");
+			if (!title.get().equals(event.title())) return HttpError.of(400,"Title mismatch!");
 			return db.add(opt.get()).map(ApiEndpoint::toJson);
 		} catch (IOException e) {
 			return error(e, "Failed to read event data from request body");
@@ -67,7 +67,7 @@ public class ApiEndpoint extends PathHandler {
 		try {
 			aid = Long.parseLong(id);
 		} catch (Exception e) {
-			return HttpError.of(400, "%s is not a valid appointment id!", id);
+			return HttpError.of(404, "%s is not a valid appointment id!", id);
 		}
 		var opt = getHeader(ex, "title");
 		if (opt.isEmpty()) return HttpError.of(412, "title missing");
@@ -83,7 +83,6 @@ public class ApiEndpoint extends PathHandler {
 		return db.removeAppointment(event.id());
 	}
 
-
 	@Override
 	public boolean doDelete(String path, HttpExchange ex) throws IOException {
 		if ("/event".equals(path)) return sendContent(ex, delete(path, ex));
@@ -94,233 +93,219 @@ public class ApiEndpoint extends PathHandler {
 	public boolean doGet(String path, HttpExchange ex) throws IOException {
 		return switch (path) {
 			case "/event" -> sendContent(ex,getEvent(ex).map(ApiEndpoint::toJson).map(ApiEndpoint::httpError));
-			case "/events/json" -> sendContent(ex,eventList(ex).map(ApiEndpoint::toJsonList).map(ApiEndpoint::httpError));
 			case "/events/ical"-> sendContent(ex,eventList(ex).map(ApiEndpoint::toIcal).map(ApiEndpoint::httpError));
-			case "/tags" -> listTags(ex);
-			default -> unknownPath(ex,path);
-		};
-	}
-
-	@Override
-	public boolean doPatch(String path, HttpExchange ex) throws IOException {
-		if ("/event".equals(path)) return sendContent(ex, updateEvent(ex));
-		return unknownPath(ex, path);
-	}
-
-	@Override
-	public boolean doPost(String path, HttpExchange ex) throws IOException {
-		if ("/event".equals(path)) return sendContent(ex, createEvent(ex));
-		return unknownPath(ex, path);
-	}
-
-	private Result<List<Appointment>> eventList(HttpExchange ex) {
-		var param = queryParam(ex);
-		var tags  = nullable(param.get(TAGS))  //
-				.stream()
-				.flatMap(s -> Arrays.stream(s.split(",")))
-				.map(s -> s.trim().toLowerCase())
-				.toList();
-
-		Result<LocalDateTime> start = parseDate(param.get(START));
-		if (start == null) start = parsePast(param.get(PAST));
-		if (start instanceof de.srsoftware.tools.Error<LocalDateTime> err) return err.transform();
-		var     startDate = (start == null) ? null:
-				start.optional().orElse(null);
-				Integer offset = null;
-
-				var o = param.get(OFFSET);
-				if (o != null) {
-					try {
-						offset = Integer.parseInt(o);
-					} catch (NumberFormatException e) {
-						return error("Offset (offset=%s) is not a number!", o);
-					}
-				}
-
-				Integer count = null;
-				o             = param.get(COUNT);
-				if (o != null) {
-					try {
-						count = Integer.parseInt(o);
-					} catch (NumberFormatException e) {
-						return error("Count (count=%s) is not a number!", o);
-					}
-				}
-
-				return db.list(startDate, null, count, offset).map(res -> filterByTags(res, tags));
+			case "/events/json" -> sendContent(ex,eventList(ex).map(ApiEndpoint::toJsonList).map(ApiEndpoint::httpError));
+            case "/tags" -> listTags(ex);
+            default -> unknownPath(ex, path);
+        };
+    }
+
+    @Override
+    public boolean doPatch(String path, HttpExchange ex) throws IOException {
+        if ("/event".equals(path)) return sendContent(ex, updateEvent(ex));
+        return unknownPath(ex, path);
+    }
+
+    @Override
+    public boolean doPost(String path, HttpExchange ex) throws IOException {
+        if ("/event".equals(path)) return sendContent(ex, createEvent(ex));
+        return unknownPath(ex, path);
+    }
+
+    private Result<List<Appointment>> eventList(HttpExchange ex) {
+        var param = queryParam(ex);
+        var tags = nullable(param.get(TAGS)).stream()
+                .flatMap(s -> Arrays.stream(s.split(",")))
+                .map(s -> s.trim().toLowerCase())
+                .toList();
+
+        Result<LocalDateTime> start = parseDate(param.get(START));
+        if (start == null)    start = parsePast(param.get(PAST));
+        if (start instanceof de.srsoftware.tools.Error<LocalDateTime> err) return err.transform();
+		var     startDate = (start == null) ? null: start.optional().orElse(null);
+		Integer offset = null;
+
+		var o = param.get(OFFSET);
+		if (o != null) try {
+			offset = Integer.parseInt(o);
+		} catch (NumberFormatException e) {
+			return HttpError.of(400,"Offset (offset=%s) is not a number!", o);
 		}
 
 
-		private Result<List<Appointment>> filterByTags(Result<List<Appointment>> res, List<String> tags) {
-			if (tags == null || tags.isEmpty()) return res;
-			var opt = res.optional();
-			if (opt.isEmpty()) return transform(res);
-			var list = opt.get().stream().filter(event -> tagsMatch(event, tags)).toList();
-			return Payload.of(list);
+		Integer count = null;
+		o	          = param.get(COUNT);
+		if (o != null) try {
+			count = Integer.parseInt(o);
+		} catch (NumberFormatException e) {
+			return HttpError.of(400,"Count (count=%s) is not a number!", o);
 		}
 
+		return db.list(startDate, null, count, offset).map(res -> filterByTags(res, tags));
+	}
 
-		private Result<Appointment> getEvent(HttpExchange ex) {
-			var params = queryParam(ex);
-			var o      = params.get(ID);
-			if (o == null) return error("id parameter missing!");
-			try {
-				long id = Long.parseLong(o);
-				return db.loadEvent(id);
-			} catch (NumberFormatException e) {
-				return error(e, "Illegal format for id parameter (%s)", o);
-			}
-		}
-
-		private static <T> Result<T> httpError(Result<T> res) {
-			if (res instanceof NotFound<T> notFound) return HttpError.of(404, notFound.message());
-			return res;
-		}
+	private Result<List<Appointment>> filterByTags(Result<List<Appointment>> res, List<String> tags) {
+		if (tags == null || tags.isEmpty()) return res;
+		var opt = res.optional();
+		if (opt.isEmpty()) return transform(res);
+		var list = opt.get().stream().filter(event -> tagsMatch(event, tags)).toList();
+		return Payload.of(list);
+	}
 
-		private boolean listTags(HttpExchange ex) throws IOException {
-			var params = queryParam(ex);
-			var infix  = params.get("infix");
-			if (infix == null) return sendContent(ex, error("No infix set in method call parameters"));
-			var res = db.findTags(infix).map(ApiEndpoint::sortTags);
-			return sendContent(ex, res);
+	private Result<Appointment> getEvent(HttpExchange ex) {
+		var params = queryParam(ex);
+		var o      = params.get(ID);
+		if (o == null) return HttpError.of(400,"id parameter missing!");
+		try {
+			return db.loadEvent(Long.parseLong(o));
+		} catch (NumberFormatException e) {
+			return HttpError.of(400,e, "Illegal format for id parameter (%s)", o);
 		}
+	}
 
-		public static Result<LocalDateTime> parseDate(String s) {
-			if (s == null) return null;
-			var matcher = DATE_TIME.matcher(s);
-			if (matcher.find()) {
-				int year   = Integer.parseInt(matcher.group(1));
-				int month  = Integer.parseInt(matcher.group(2));
-				int day    = nullable(matcher.group(4)).map(Integer::parseInt).orElse(1);
-				int hour   = nullable(matcher.group(6)).map(Integer::parseInt).orElse(0);
-				int minute = nullable(matcher.group(7)).map(Integer::parseInt).orElse(0);
-				int second = nullable(matcher.group(9)).map(Integer::parseInt).orElse(0);
-				return Payload.of(LocalDateTime.of(year, month, day, hour, minute, second));
-			}
-			return error("invalid date time format: %s", s);
-		}
+	private static <T> Result<T> httpError(Result<T> res) {
+		if (res instanceof NotFound<T> notFound) return HttpError.of(404, notFound.message());
+		return res;
+	}
 
+	private boolean listTags(HttpExchange ex) throws IOException {
+		var params = queryParam(ex);
+		var infix  = nullIfEmpty(params.get("infix"));
+		if (infix == null) return sendContent(ex, HttpError.of(400,"No infix set in method call parameters"));
+		var res = db.findTags(infix).map(ApiEndpoint::sortTags);
+		return sendContent(ex, res);
+	}
 
-		public static Result<LocalDateTime> parsePast(String s) {
-			var start = LocalDateTime.now().withDayOfMonth(1).withHour(0).withMinute(0).withSecond(0).withNano(0);
-			if (s == null) return Payload.of(start);
-			var matcher = PAST_PATTERN.matcher(s);
-			if (matcher.find()) {
-				for (int i = 0; i <= matcher.groupCount(); i++) System.out.printf("%s: %s\n", i, matcher.group(i));
-
-				int num = nullable(matcher.group(1)).map(Integer::parseInt).orElse(0);
-				switch (nullable(matcher.group(2)).orElse("")) {
-					case "m":
-						start = start.minusMonths(num);
-						break;
-					case "y":
-						start = start.minusYears(num);
-						break;
-				}
-				var all = matcher.group(3);
-				if ("all".equals(all)) return null;
-				return Payload.of(start);
-			}
-			return error("invalid past format: %s", s);
+	public static Result<LocalDateTime> parseDate(String s) {
+		if (s == null) return null;
+		var matcher = DATE_TIME.matcher(s);
+		if (matcher.find()) {
+			int year   = Integer.parseInt(matcher.group(1));
+			int month  = Integer.parseInt(matcher.group(2));
+			int day    = nullable(matcher.group(4)).map(Integer::parseInt).orElse(1);
+			int hour   = nullable(matcher.group(6)).map(Integer::parseInt).orElse(0);
+			int minute = nullable(matcher.group(7)).map(Integer::parseInt).orElse(0);
+			int second = nullable(matcher.group(9)).map(Integer::parseInt).orElse(0);
+			return Payload.of(LocalDateTime.of(year, month, day, hour, minute, second));
 		}
+		return error("invalid date time format: %s", s);
+	}
 
-		private static Result<List<String>> sortTags(Result<List<String>> listResult) {
-			if (listResult.optional().isEmpty()) return listResult;
-			List<String> list = listResult.optional().get();
-			while (list.size() > 15) {
-				int longest = list.stream().map(String::length).reduce(0, Integer::max);
-				var subset  = list.stream().filter(s -> s.length() < longest).toList();
-				if (subset.size() < 3) return Payload.of(list);
-				list = subset;
+	public static Result<LocalDateTime> parsePast(String s) {
+		var start = LocalDateTime.now().withDayOfMonth(1).withHour(0).withMinute(0).withSecond(0).withNano(0);
+		if (s == null) return Payload.of(start);
+		var matcher = PAST_PATTERN.matcher(s);
+		if (matcher.find()) {
+			int num = nullable(matcher.group(1)).map(Integer::parseInt).orElse(0);
+			var g2 = nullable(matcher.group(2)).orElse("");
+			switch (g2) {
+				case "m":
+					start = start.minusMonths(num);
+					break;
+				case "y":
+					start = start.minusYears(num);
+					break;
 			}
-			return Payload.of(list);
+			var all = matcher.group(3);
+			if ("all".equals(all)) return null;
+			return Payload.of(start);
 		}
+		return error("invalid past format: %s", s);
+	}
 
-
-		private static boolean tagsMatch(Appointment event, List<String> tags) {
-			return new HashSet<>(event.tags().stream().map(String::toLowerCase).toList()).containsAll(tags);
+	private static Result<List<String>> sortTags(Result<List<String>> listResult) {
+		if (listResult.optional().isEmpty()) return listResult;
+		List<String> list = listResult.optional().get();
+		while (list.size() > 15) {
+			int longest = list.stream().map(String::length).reduce(0, Integer::max);
+			var subset  = list.stream().filter(s -> s.length() < longest).toList();
+			if (subset.size() < 3) return Payload.of(list);
+			list = subset;
 		}
+		return Payload.of(list);
+	}
 
+	private static boolean tagsMatch(Appointment event, List<String> tags) {
+		return new HashSet<>(event.tags().stream().map(String::toLowerCase).toList()).containsAll(tags);
+	}
 
-		private Result<BaseAppointment> toEvent(JSONObject json) {
-			var description = json.has(DESCRIPTION) ? nullIfEmpty(json.getString(DESCRIPTION)) : null;
-			var title	= json.has(TITLE) ? nullIfEmpty(json.getString(TITLE)) : null;
-			if (title == null) return error("title missing");
-			var start = json.has(START) ? nullIfEmpty(json.getString(START)) : null;
-			if (start == null) return error("start missing");
-			var startDate = nullable(start).map(dt -> LocalDateTime.parse(dt, ISO_DATE_TIME)).orElse(null);
-			var end       = json.has(END) ? nullIfEmpty(json.getString(END)) : null;
-			var endDate   = nullable(end).map(dt -> LocalDateTime.parse(dt, ISO_DATE_TIME)).orElse(null);
-			var location  = json.has(LOCATION) ? json.getString(LOCATION) : null;
-			if (location == null) return error("location missing");
-			var aid   = json.has(AID) ? json.getLong(AID) : 0;
-			var event = new BaseAppointment(aid, title, description, startDate, endDate, location);
-			if (json.has(ATTACHMENTS)) {
-				json.getJSONArray(ATTACHMENTS).forEach(att -> {
-					Payload  //
-					    .of(att.toString())
-					    .map(BaseImporter::url)
-					    .map(BaseImporter::toAttachment)
-					    .optional()
-					    .ifPresent(event::add);
-				});
-			}
-			if (json.has(LINKS)) {
-				json.getJSONArray(LINKS).forEach(o -> {
-					if (o instanceof JSONObject j) toLink(j).optional().ifPresent(event::addLinks);
-				});
-			}
-			if (json.has(TAGS)) json.getJSONArray(TAGS).forEach(o -> event.tags(o.toString()));
-			return Payload.of(event);
+	private Result<BaseAppointment> toEvent(JSONObject json) {
+		var description = json.has(DESCRIPTION) ? nullIfEmpty(json.getString(DESCRIPTION)) : null;
+		var title	= json.has(TITLE) ? nullIfEmpty(json.getString(TITLE)) : null;
+		if (title == null) return error("title missing");
+		var start = json.has(START) ? nullIfEmpty(json.getString(START)) : null;
+		if (start == null) return error("start missing");
+		var startDate = nullable(start).map(dt -> LocalDateTime.parse(dt, ISO_DATE_TIME)).orElse(null);
+		var end       = json.has(END) ? nullIfEmpty(json.getString(END)) : null;
+		var endDate   = nullable(end).map(dt -> LocalDateTime.parse(dt, ISO_DATE_TIME)).orElse(null);
+		var location  = json.has(LOCATION) ? json.getString(LOCATION) : null;
+		if (location == null) return error("location missing");
+		var aid   = json.has(AID) ? json.getLong(AID) : 0;
+		var event = new BaseAppointment(aid, title, description, startDate, endDate, location);
+		if (json.has(ATTACHMENTS)) {
+			json.getJSONArray(ATTACHMENTS).forEach(att -> {
+				Payload  //
+					.of(att.toString())
+					.map(BaseImporter::url)
+					.map(BaseImporter::toAttachment)
+					.optional()
+					.ifPresent(event::add);
+			});
 		}
+		if (json.has(LINKS)) json.getJSONArray(LINKS).forEach(o -> {
+			if (o instanceof JSONObject j) toLink(j).optional().ifPresent(event::addLinks);
+		});
 
+		if (json.has(TAGS)) json.getJSONArray(TAGS).forEach(o -> event.tags(o.toString()));
+		return Payload.of(event);
+	}
 
-		private static Result<String> toIcal(Result<List<Appointment>> res) {
-			var opt = res.optional();
-			if (opt.isEmpty()) return transform(res);
-			var list = opt.get().stream().map(Appointment::ical).collect(Collectors.joining("\n"));
-			return Payload.of(list);
-		}
-
+	private static Result<String> toIcal(Result<List<Appointment>> res) {
+		var opt = res.optional();
+		if (opt.isEmpty()) return transform(res);
+		var list = opt.get().stream().map(Appointment::ical).collect(Collectors.joining("\n"));
+		return Payload.of(list);
+	}
 
-		private static Result<JSONObject> toJson(Result<? extends Appointment> res) {
-			var opt = res.optional();
-			if (opt.isEmpty()) return transform(res);
-			return Payload.of(opt.get().json());
-		}
+	private static Result<JSONObject> toJson(Result<? extends Appointment> res) {
+		var opt = res.optional();
+		return opt.isEmpty() ? transform(res) : Payload.of(opt.get().json());
+	}
 
-		private static Result<List<JSONObject>> toJsonList(Result<List<Appointment>> res) {
-			var opt = res.optional();
-			if (opt.isEmpty()) return transform(res);
-			var list = opt.get().stream().map(Appointment::json).toList();
-			return Payload.of(list);
-		}
-		protected static Result<Link> toLink(JSONObject json) {
-			try {
-				var description = json.getString(DESCRIPTION);
-				return Payload.of(json.getString(URL)).map(BaseImporter::url).map(url -> BaseImporter.link(url, description));
+	private static Result<List<JSONObject>> toJsonList(Result<List<Appointment>> res) {
+		var opt = res.optional();
+		if (opt.isEmpty()) return transform(res);
+		var list = opt.get().stream().map(Appointment::json).toList();
+		return Payload.of(list);
+	}
 
-			} catch (Exception e) {
-				return error(e, "Failed to create link from %s", json);
-			}
-		}
-		private boolean unknownPath(HttpExchange ex, String path) throws IOException {
-			return sendContent(ex, HttpError.of(404, "%s is not known to this API", path));
+	protected static Result<Link> toLink(JSONObject json) {
+		try {
+			var description = json.getString(DESCRIPTION);
+			return Payload.of(json.getString(URL))
+					.map(BaseImporter::url)
+					.map(url -> BaseImporter.link(url, description));
+		} catch (Exception e) {
+			return error(e, "Failed to create link from %s", json);
 		}
+	}
 
+	private boolean unknownPath(HttpExchange ex, String path) throws IOException {
+		return sendContent(ex, HttpError.of(404, "%s is not known to this API", path));
+	}
 
-		private Result<JSONObject> updateEvent(HttpExchange ex) {
-			try {
-				var res = toEvent(json(ex));
-				var opt = res.optional();
-				if (opt.isEmpty()) return transform(res);
-				var event = opt.get();
-				var title = getHeader(ex, TITLE);
-				if (title.isEmpty()) return error("Missing title header");
-				if (!title.get().equals(event.title())) return error("Title mismatch!");
-				return db.update(opt.get()).map(ApiEndpoint::toJson);
-			} catch (IOException e) {
-				return error(e, "Failed to read event data from request body");
-			}
+	private Result<JSONObject> updateEvent(HttpExchange ex) {
+		try {
+			var res = toEvent(json(ex));
+			var opt = res.optional();
+			if (opt.isEmpty()) return transform(res);
+			var event = opt.get();
+			var title = getHeader(ex, TITLE);
+			if (title.isEmpty()) return HttpError.of(400,"Missing title header");
+			if (!title.get().equals(event.title())) return HttpError.of(400,"Title mismatch!");
+			return db.update(opt.get()).map(ApiEndpoint::toJson);
+		} catch (IOException e) {
+			return error(e, "Failed to read event data from request body");
 		}
 	}
+}
diff --git a/de.srsoftware.cal.web/src/main/java/de/srsoftware/cal/IndexHandler.java b/de.srsoftware.cal.web/src/main/java/de/srsoftware/cal/IndexHandler.java
index 7da488b..b05c6b7 100644
--- a/de.srsoftware.cal.web/src/main/java/de/srsoftware/cal/IndexHandler.java
+++ b/de.srsoftware.cal.web/src/main/java/de/srsoftware/cal/IndexHandler.java
@@ -7,6 +7,7 @@ import java.io.IOException;
 
 public class IndexHandler extends PathHandler {
 	PathHandler staticPages;
+
 	public IndexHandler(PathHandler staticPages) {
 		this.staticPages = staticPages;
 	}
@@ -14,10 +15,9 @@ public class IndexHandler extends PathHandler {
 	@Override
 	public boolean doGet(String path, HttpExchange ex) throws IOException {
 		return switch (path) {
-			case "/" -> staticPages.doGet("/index", ex);
-			case "/favicon.ico" -> staticPages.doGet("/images/%s".formatted(path), ex);
-			default -> super.doGet(path, ex);
-		};
-
-	}
+            case "/" -> staticPages.doGet("/index", ex);
+            case "/favicon.ico" -> staticPages.doGet("/images/%s".formatted(path), ex);
+            default -> super.doGet(path, ex);
+        };
+    }
 }
diff --git a/de.srsoftware.cal.web/src/main/java/de/srsoftware/cal/StaticHandler.java b/de.srsoftware.cal.web/src/main/java/de/srsoftware/cal/StaticHandler.java
index ae9c1b6..677bda9 100644
--- a/de.srsoftware.cal.web/src/main/java/de/srsoftware/cal/StaticHandler.java
+++ b/de.srsoftware.cal.web/src/main/java/de/srsoftware/cal/StaticHandler.java
@@ -8,7 +8,6 @@ import java.io.IOException;
 import java.nio.file.Path;
 import java.util.Optional;
 
-
 public class StaticHandler extends PathHandler {
 	private final Optional<String> staticPath;
 
diff --git a/de.srsoftware.cal.web/src/main/resources/script/index.js b/de.srsoftware.cal.web/src/main/resources/script/index.js
index ecc8f16..fb46b76 100644
--- a/de.srsoftware.cal.web/src/main/resources/script/index.js
+++ b/de.srsoftware.cal.web/src/main/resources/script/index.js
@@ -118,7 +118,7 @@ function openIcal(){
     var pos = url.indexOf('?');
     if (pos>1) url = url.substring(0,pos);
     if (!url.endsWith('/')) url += '/';
-    url += 'api/ical'+query;
+    url += 'api/events/ical'+query;
     var elem = create('a');
     elem.setAttribute('href',url);
     elem.setAttribute('download','calendar.ical');
diff --git a/doc/openapi3_0.yaml b/doc/openapi3_0.yaml
index 8f4125f..1bcd0b2 100644
--- a/doc/openapi3_0.yaml
+++ b/doc/openapi3_0.yaml
@@ -266,6 +266,14 @@ paths:
                 items:
                   type: string
                 type: array
+        '400':
+          description: invalid input
+          content:
+            application/json:
+              schema:
+                type: string
+              example: {"message":"No infix set in method call parameters"}
+
 components:
   schemas:
     Appointment: