diff --git a/packages/frontend/editor-ui/src/features/agents/__tests__/AgentSkillModal.test.ts b/packages/frontend/editor-ui/src/features/agents/__tests__/AgentSkillModal.test.ts
index 33c1a58653d..0fb47b1181f 100644
--- a/packages/frontend/editor-ui/src/features/agents/__tests__/AgentSkillModal.test.ts
+++ b/packages/frontend/editor-ui/src/features/agents/__tests__/AgentSkillModal.test.ts
@@ -5,7 +5,10 @@ import { mockedStore } from '@/__tests__/utils';
 import { useUIStore } from '@/app/stores/ui.store';
 import { fireEvent } from '@testing-library/vue';
 import { defineComponent, h, onMounted, watch } from 'vue';
-import { AGENT_SKILL_REFERENCE_MAX_COUNT } from '@n8n/api-types';
+import {
+	AGENT_SKILL_INSTRUCTIONS_MAX_LENGTH,
+	AGENT_SKILL_REFERENCE_MAX_COUNT,
+} from '@n8n/api-types';
 
 import AgentSkillModal from '../components/AgentSkillModal.vue';
 import type { AgentSkill } from '../types';
@@ -20,6 +23,11 @@ vi.mock('../composables/useAgentApi', () => ({
 	createAgentSkill: (...args: unknown[]) => apiCreateSpy(...args),
 }));
 
+const { showMessage } = vi.hoisted(() => ({ showMessage: vi.fn() }));
+vi.mock('@n8n/composables/useToast', () => ({
+	useToast: () => ({ showMessage }),
+}));
+
 const ModalStub = defineComponent({
 	props: ['name', 'customClass', 'width'],
 	template: `
@@ -42,7 +50,9 @@ const SkillViewerStub = defineComponent({
 			return Boolean(
 				props.skill?.name?.trim() &&
 					props.skill?.description?.trim() &&
-					props.skill?.instructions?.trim(),
+					props.skill?.instructions?.trim() &&
+					new TextEncoder().encode(props.skill.instructions).byteLength <=
+						AGENT_SKILL_INSTRUCTIONS_MAX_LENGTH,
 			);
 		}
 		onMounted(() => emit('update:valid', computeValid()));
@@ -139,6 +149,35 @@ describe('AgentSkillModal', () => {
 
 		expect(onConfirm).not.toHaveBeenCalled();
 		expect(uiStore.closeModal).not.toHaveBeenCalled();
+		expect(showMessage).toHaveBeenCalledWith({
+			title: 'agents.builder.skills.saveError',
+			message: 'agents.builder.skills.validation.descriptionRequired',
+			type: 'error',
+		});
+	});
+
+	it('explains why overlong instructions cannot be saved', async () => {
+		const onConfirm = vi.fn();
+		const { container } = renderModal({
+			onConfirm,
+			skill: {
+				name: 'Research',
+				description: 'Use for research',
+				instructions: 'x'.repeat(AGENT_SKILL_INSTRUCTIONS_MAX_LENGTH + 1),
+			},
+		});
+
+		await fireEvent.click(
+			container.querySelector('[data-testid="agent-skill-create-save"]') as Element,
+		);
+
+		expect(onConfirm).not.toHaveBeenCalled();
+		expect(uiStore.closeModal).not.toHaveBeenCalled();
+		expect(showMessage).toHaveBeenCalledWith({
+			title: 'agents.builder.skills.saveError',
+			message: 'agents.builder.skills.validation.instructionsMaxLength',
+			type: 'error',
+		});
 	});
 
 	it('adds and removes references from the file navigation', async () => {
diff --git a/packages/frontend/editor-ui/src/features/agents/components/AgentSkillModal.vue b/packages/frontend/editor-ui/src/features/agents/components/AgentSkillModal.vue
index 0a450dd53f2..a648f6902c4 100644
--- a/packages/frontend/editor-ui/src/features/agents/components/AgentSkillModal.vue
+++ b/packages/frontend/editor-ui/src/features/agents/components/AgentSkillModal.vue
@@ -1,10 +1,14 @@
 <script setup lang="ts">
 import { computed, ref } from 'vue';
-import { AGENT_SKILL_REFERENCE_MAX_COUNT } from '@n8n/api-types';
+import {
+	AGENT_SKILL_INSTRUCTIONS_MAX_LENGTH,
+	AGENT_SKILL_REFERENCE_MAX_COUNT,
+} from '@n8n/api-types';
 import { N8nButton, N8nCallout, N8nHeading, N8nIcon } from '@n8n/design-system';
 import { useI18n, type BaseTextKey } from '@n8n/i18n';
 
 import Modal from '@/app/components/Modal.vue';
+import { useToast } from '@n8n/composables/useToast';
 import { useUIStore } from '@/app/stores/ui.store';
 import { useAgentTelemetry } from '../composables/useAgentTelemetry';
 import type { AgentSkill } from '../types';
@@ -37,6 +41,7 @@ const props = defineProps<{
 const i18n = useI18n();
 const uiStore = useUIStore();
 const agentTelemetry = useAgentTelemetry();
+const { showMessage } = useToast();
 
 const skill = ref<AgentSkill>(
 	normalizeSkill({
@@ -84,6 +89,13 @@ const validationErrors = computed<Partial<Record<keyof AgentSkill, string>>>(()
 
 	if (!instructions) {
 		errors.instructions = i18n.baseText('agents.builder.skills.validation.instructionsRequired');
+	} else if (
+		new TextEncoder().encode(skill.value.instructions).byteLength >
+		AGENT_SKILL_INSTRUCTIONS_MAX_LENGTH
+	) {
+		errors.instructions = i18n.baseText('agents.builder.skills.validation.instructionsMaxLength', {
+			interpolate: { max: String(AGENT_SKILL_INSTRUCTIONS_MAX_LENGTH) },
+		});
 	}
 	if (skill.value.references?.some((reference) => !reference.content.trim())) {
 		errors.references = i18n.baseText('agents.builder.skills.references.invalidSummary');
@@ -168,7 +180,19 @@ function closeModal() {
 
 function onSave() {
 	submitted.value = true;
-	if (!canSave.value) return;
+	if (!canSave.value) {
+		const message =
+			validationErrors.value.name ??
+			validationErrors.value.description ??
+			validationErrors.value.instructions ??
+			validationErrors.value.references;
+		showMessage({
+			title: i18n.baseText('agents.builder.skills.saveError'),
+			...(message ? { message } : {}),
+			type: 'error',
+		});
+		return;
+	}
 
 	const payload = normalizeSkill({
 		name: skill.value.name.trim(),
diff --git a/packages/frontend/editor-ui/src/features/agents/composables/useAgentCapabilitiesActions.test.ts b/packages/frontend/editor-ui/src/features/agents/composables/useAgentCapabilitiesActions.test.ts
index f90a6edfed2..4dcca0374da 100644
--- a/packages/frontend/editor-ui/src/features/agents/composables/useAgentCapabilitiesActions.test.ts
+++ b/packages/frontend/editor-ui/src/features/agents/composables/useAgentCapabilitiesActions.test.ts
@@ -156,7 +156,7 @@ describe('useAgentCapabilitiesActions', () => {
 
 	it('saves a skill-modal confirm for the agent it was opened on', () => {
 		const skill: AgentSkill = { name: 'PR Reviewer', description: '', instructions: 'Review.' };
-		const { actions, scheduleSkillSave, agent } = makeActions({
+		const { actions, scheduleConfigUpdate, scheduleSkillSave, agent } = makeActions({
 			skills: [{ type: 'skill', id: 's1' }],
 		} as Partial<AgentJsonConfig>);
 		agent.value = { id: 'agent-1', skills: { s1: skill } } as unknown as AgentResource;
@@ -171,6 +171,28 @@ describe('useAgentCapabilitiesActions', () => {
 			skillId: 's1',
 			skill: expect.objectContaining({ instructions: 'Edited.' }),
 		});
+		expect(scheduleConfigUpdate).not.toHaveBeenCalled();
+	});
+
+	it('persists a skill rename without scheduling a config save', () => {
+		const skill: AgentSkill = { name: 'PR Reviewer', description: '', instructions: 'Review.' };
+		const { actions, scheduleConfigUpdate, scheduleSkillSave, agent } = makeActions({
+			skills: [{ type: 'skill', id: 's1' }],
+		} as Partial<AgentJsonConfig>);
+		agent.value = { id: 'agent-1', skills: { s1: skill } } as unknown as AgentResource;
+
+		actions.onOpenSkillFromList('s1');
+		const modalData = openModalWithData.mock.calls[0][0] as {
+			data: { onConfirm: (payload: { id?: string; skill: AgentSkill }) => void };
+		};
+		modalData.data.onConfirm({ id: 's1', skill: { ...skill, name: 'Renamed skill' } });
+
+		expect(scheduleSkillSave).toHaveBeenCalledWith({
+			skillId: 's1',
+			skill: expect.objectContaining({ name: 'Renamed skill' }),
+		});
+		expect(scheduleConfigUpdate).not.toHaveBeenCalled();
+		expect(agent.value.skills?.s1?.name).toBe('Renamed skill');
 	});
 
 	it('drops the tool ref from the config when onRemoveTool removes it', () => {
diff --git a/packages/frontend/editor-ui/src/features/agents/composables/useAgentCapabilitiesActions.ts b/packages/frontend/editor-ui/src/features/agents/composables/useAgentCapabilitiesActions.ts
index b9040bfaf64..75b2aacb6de 100644
--- a/packages/frontend/editor-ui/src/features/agents/composables/useAgentCapabilitiesActions.ts
+++ b/packages/frontend/editor-ui/src/features/agents/composables/useAgentCapabilitiesActions.ts
@@ -306,12 +306,6 @@ export function useAgentCapabilitiesActions(deps: UseAgentCapabilitiesActionsDep
 							[skillId]: sanitizedSkill,
 						},
 					};
-					const nextSkills = [...(localConfig.value?.skills ?? [])];
-					const skillRefIndex = nextSkills.findIndex((skillRef) => skillRef.id === id);
-					if (skillRefIndex !== -1) {
-						nextSkills[skillRefIndex] = { type: 'skill', id: skillId };
-						scheduleConfigUpdate({ skills: nextSkills });
-					}
 					scheduleSkillSave({ skillId, skill: sanitizedSkill });
 				},
 			},