diff --git a/keyext.api/src/main/java/org/keyproject/key/api/KeyApiImpl.java b/keyext.api/src/main/java/org/keyproject/key/api/KeyApiImpl.java
index 105ffdae8b..3005cda089 100644
--- a/keyext.api/src/main/java/org/keyproject/key/api/KeyApiImpl.java
+++ b/keyext.api/src/main/java/org/keyproject/key/api/KeyApiImpl.java
@@ -10,11 +10,14 @@
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
+import java.util.Map;
+import java.util.NoSuchElementException;
 import java.util.Objects;
 import java.util.Stack;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Function;
+import java.util.stream.Collectors;
 import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
 
@@ -86,9 +89,23 @@ public void taskFinished(TaskFinishedInfo info) {
     };
     private final AtomicInteger uniqueCounter = new AtomicInteger();
 
+    // Available macros and script commands are discovered via the service loader
+    // (a classpath scan). They don't change at runtime, so scan once here instead
+    // of on every getAvailableMacros/getAvailableScriptCommands/macro request.
+    private final List<ProofMacro> availableMacros = loadAll(ProofMacro.class);
+    private final List<ProofScriptCommand> availableScriptCommands =
+        loadAll(ProofScriptCommand.class);
+    private final Map<String, ProofMacro> macrosByName = availableMacros.stream()
+            .collect(Collectors.toUnmodifiableMap(ProofMacro::getName, m -> m, (a, b) -> a));
+
     public KeyApiImpl() {
     }
 
+    private static <T> List<T> loadAll(Class<T> service) {
+        return StreamSupport.stream(
+            ClassLoaderUtil.loadServices(service).spliterator(), false).toList();
+    }
+
     @Override
     @JsonRequest
     public CompletableFuture<List<ExampleDesc>> examples() {
@@ -124,18 +141,13 @@ public CompletableFuture<String> getVersion() {
     @Override
     public CompletableFuture<List<ProofMacroDesc>> getAvailableMacros() {
         return CompletableFuture.completedFuture(
-            StreamSupport
-                    .stream(ClassLoaderUtil.loadServices(ProofMacro.class).spliterator(), false)
-                    .map(ProofMacroDesc::from).toList());
+            availableMacros.stream().map(ProofMacroDesc::from).toList());
     }
 
     @Override
     public CompletableFuture<List<ProofScriptCommandDesc>> getAvailableScriptCommands() {
         return CompletableFuture.completedFuture(
-            StreamSupport
-                    .stream(ClassLoaderUtil.loadServices(ProofScriptCommand.class).spliterator(),
-                        false)
-                    .map(ProofScriptCommandDesc::from).toList());
+            availableScriptCommands.stream().map(ProofScriptCommandDesc::from).toList());
     }
 
     @Override
@@ -162,9 +174,10 @@ public CompletableFuture<MacroStatistic> macro(ProofId proofId, String macroName
         return CompletableFuture.supplyAsync(() -> {
             var proof = data.find(proofId);
             var env = data.find(proofId.env());
-            var macro = StreamSupport
-                    .stream(ClassLoaderUtil.loadServices(ProofMacro.class).spliterator(), false)
-                    .filter(it -> it.getName().equals(macroName)).findFirst().orElseThrow();
+            var macro = macrosByName.get(macroName);
+            if (macro == null) {
+                throw new NoSuchElementException("No macro named '" + macroName + "'");
+            }
 
             try {
                 var info =
diff --git a/keyext.api/src/test/java/org/keyproject/key/api/KeyApiServiceCacheTest.java b/keyext.api/src/test/java/org/keyproject/key/api/KeyApiServiceCacheTest.java
new file mode 100644
index 0000000000..8c432bb7e5
--- /dev/null
+++ b/keyext.api/src/test/java/org/keyproject/key/api/KeyApiServiceCacheTest.java
@@ -0,0 +1,36 @@
+/* This file is part of KeY - https://key-project.org
+ * KeY is licensed under the GNU General Public License Version 2
+ * SPDX-License-Identifier: GPL-2.0-only */
+package org.keyproject.key.api;
+
+import java.util.NoSuchElementException;
+import java.util.concurrent.ExecutionException;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests for the cached service-loader lookups (macros / script commands). The
+ * caching is by construction; these guard against regressions in the behaviour.
+ */
+class KeyApiServiceCacheTest {
+    @Test
+    void availableMacrosAndCommandsAreNonEmptyAndStable() throws Exception {
+        var api = new KeyApiImpl();
+        var macros1 = api.getAvailableMacros().get();
+        var macros2 = api.getAvailableMacros().get();
+        Assertions.assertFalse(macros1.isEmpty(), "expected built-in macros");
+        Assertions.assertEquals(macros1, macros2, "repeated calls must be consistent");
+        Assertions.assertFalse(api.getAvailableScriptCommands().get().isEmpty(),
+            "expected built-in script commands");
+    }
+
+    @Test
+    void macroRejectsUnknownName() throws Exception {
+        var api = new KeyApiImpl();
+        var proofId = api.loadTerm("true").get();
+        var ex = Assertions.assertThrows(ExecutionException.class,
+            () -> api.macro(proofId, "definitely-not-a-real-macro", null).get());
+        Assertions.assertInstanceOf(NoSuchElementException.class, ex.getCause());
+    }
+}