diff --git a/apps/web/src/agent/context.ts b/apps/web/src/agent/context.ts
index 5b6b9557..2cbf8a91 100644
--- a/apps/web/src/agent/context.ts
+++ b/apps/web/src/agent/context.ts
@@ -617,6 +617,66 @@ export const EditorContextAdapter = {
 			appliedParams: element.params,
 		};
 	},
+
+	updateEffectElement({
+		elementId,
+		params,
+	}: {
+		elementId: string;
+		params: Record<string, number | string | boolean>;
+	}):
+		| {
+				success: boolean;
+				elementId: string;
+				appliedParams: Record<string, number | string | boolean>;
+		  }
+		| { error: string } {
+		const core = EditorCore.getInstance();
+		const activeScene = core.scenes.getActiveSceneOrNull();
+		if (!activeScene) {
+			return { error: "No active timeline" };
+		}
+
+		const [resolved] = findTimelineElementsWithTracksByIds({
+			tracks: activeScene.tracks,
+			elementIds: [elementId],
+		});
+		if (!resolved) {
+			return { error: `Timeline element not found: ${elementId}` };
+		}
+		if (resolved.element.type !== "effect") {
+			return { error: "Element is not an effect" };
+		}
+
+		const effectElement = resolved.element as import("@/lib/timeline/types").EffectElement;
+		const definition = effectsRegistry.get(effectElement.effectType);
+		if (!definition) {
+			return { error: `Effect not found: ${effectElement.effectType}` };
+		}
+
+		const validationError = validateEffectParams(definition.params, params);
+		if (validationError) {
+			return { error: validationError };
+		}
+
+		const mergedParams = { ...effectElement.params, ...params };
+
+		core.timeline.updateElements({
+			updates: [
+				{
+					trackId: resolved.track.id,
+					elementId,
+					patch: { params: mergedParams } as Partial<import("@/lib/timeline/types").TimelineElement>,
+				},
+			],
+		});
+
+		return {
+			success: true,
+			elementId,
+			appliedParams: mergedParams,
+		};
+	},
 };
 
 function secondsToTicks(seconds: number): number {
diff --git a/apps/web/src/agent/tools/index.ts b/apps/web/src/agent/tools/index.ts
index 9c73cce2..c21904fe 100644
--- a/apps/web/src/agent/tools/index.ts
+++ b/apps/web/src/agent/tools/index.ts
@@ -23,3 +23,4 @@ import "@/agent/tools/update-text.tool";
 import "@/agent/tools/list-effects.tool";
 import "@/agent/tools/get-effect.tool";
 import "@/agent/tools/apply-effect.tool";
+import "@/agent/tools/update-effect.tool";
diff --git a/apps/web/src/agent/tools/schemas.ts b/apps/web/src/agent/tools/schemas.ts
index 24e788a1..cb0bc7c1 100644
--- a/apps/web/src/agent/tools/schemas.ts
+++ b/apps/web/src/agent/tools/schemas.ts
@@ -161,6 +161,16 @@ export const applyEffectSchema: ToolSchema = {
 	],
 };
 
+export const updateEffectSchema: ToolSchema = {
+	name: "update_effect",
+	description:
+		"Updates parameters of an existing effect element on the timeline. Use list_timeline to find the elementId of the effect, then pass the params you want to change. Only the provided parameters are updated; others keep their current values. Use get_effect to discover valid parameter keys and ranges.",
+	parameters: [
+		{ key: "elementId", type: "string", required: true },
+		{ key: "params", type: "object", required: true },
+	],
+};
+
 /**
  * The exact list of schemas exposed to the LLM.
  * Excludes internal-only tools (transcribe_video, mock).
@@ -179,4 +189,5 @@ export const providerToolSchemas: ToolSchema[] = [
 	listEffectsSchema,
 	getEffectSchema,
 	applyEffectSchema,
+	updateEffectSchema,
 ];
diff --git a/apps/web/src/agent/tools/update-effect.tool.ts b/apps/web/src/agent/tools/update-effect.tool.ts
new file mode 100644
index 00000000..f81d8990
--- /dev/null
+++ b/apps/web/src/agent/tools/update-effect.tool.ts
@@ -0,0 +1,39 @@
+import type { AgentContext, ToolDefinition } from "@/agent/types";
+import { toolRegistry } from "@/agent/tools/registry";
+import { updateEffectSchema } from "@/agent/tools/schemas";
+import { EditorContextAdapter } from "@/agent/context";
+
+const updateEffectTool: ToolDefinition = {
+	...updateEffectSchema,
+	execute: async (
+		args: Record<string, unknown>,
+		_context: AgentContext,
+	): Promise<
+		| {
+				success: boolean;
+				elementId: string;
+				appliedParams: Record<string, number | string | boolean>;
+		  }
+		| { error: string }
+	> => {
+		const elementId = args.elementId;
+		const params = args.params as
+			| Record<string, number | string | boolean>
+			| undefined;
+
+		if (typeof elementId !== "string" || !elementId.trim()) {
+			return { error: "Invalid element id" };
+		}
+
+		if (!params || typeof params !== "object" || Object.keys(params).length === 0) {
+			return { error: "params is required and must be a non-empty object" };
+		}
+
+		return EditorContextAdapter.updateEffectElement({
+			elementId,
+			params,
+		});
+	},
+};
+
+toolRegistry.register(updateEffectSchema.name, updateEffectTool);
diff --git a/docs/agent-tool-specs.md b/docs/agent-tool-specs.md
index c29a75b6..6b07c2be 100644
--- a/docs/agent-tool-specs.md
+++ b/docs/agent-tool-specs.md
@@ -654,6 +654,49 @@ Agregar un efecto como elemento standalone al timeline en una pista de efectos,
 
 ---
 
+## 17. `update_effect`
+
+### Propósito
+Actualizar los parámetros de un elemento de efecto existente en el timeline. Solo se actualizan los parámetros proporcionados; el resto mantiene sus valores actuales.
+
+### Input
+```ts
+{
+  elementId: string;
+  params: Record<string, number | string | boolean>;
+}
+```
+
+### Output
+```ts
+{
+  success: boolean;
+  elementId: string;
+  appliedParams: Record<string, number | string | boolean>;
+}
+```
+
+### Requirements
+- MUST validate `elementId` exists in the active timeline.
+- MUST validate the target element is an effect element (`type: "effect"`).
+- MUST validate `params` against the effect's parameter definitions (types, ranges).
+- MUST merge provided `params` with existing params (only override specified keys).
+- MUST use `updateElements` to apply the param patch.
+- MUST preserve undo/redo behavior.
+- MUST return the full merged params after update.
+
+### Errors
+- Invalid element id: `{ error: "Invalid element id" }`.
+- Missing params: `{ error: "params is required and must be a non-empty object" }`.
+- No active timeline: `{ error: "No active timeline" }`.
+- Missing element: `{ error: "Timeline element not found: <id>" }`.
+- Wrong type: `{ error: "Element is not an effect" }`.
+- Effect not found: `{ error: "Effect not found: <type>" }`.
+- Unknown parameter: `{ error: "Unknown parameter: <key>" }`.
+- Out of range: `{ error: "Parameter '<key>' must be >= <min>" }`.
+
+---
+
 ## Existing/secondary tool: `transcribe_video`
 
 ### Propósito