diff --git a/packages/core/src/PageAgentCore.ts b/packages/core/src/PageAgentCore.ts
index d1a4ac6..ce5ebeb 100644
--- a/packages/core/src/PageAgentCore.ts
+++ b/packages/core/src/PageAgentCore.ts
@@ -248,16 +248,16 @@ export class PageAgentCore extends EventTarget {
 					{ role: 'user' as const, content: await this.#assembleUserPrompt() },
 				]
 
-				const tools = { AgentOutput: this.#packMacroTool() }
+				const macroTool = { AgentOutput: this.#packMacroTool() }
 
 				// invoke LLM
 
 				console.log(chalk.blue.bold('🧠 Thinking...'))
 				this.#emitActivity({ type: 'thinking' })
 
-				const result = await this.#llm.invoke(messages, tools, this.#abortController.signal, {
+				const result = await this.#llm.invoke(messages, macroTool, this.#abortController.signal, {
 					toolChoiceName: 'AgentOutput',
-					normalizeResponse,
+					normalizeResponse: (res) => normalizeResponse(res, this.tools),
 				})
 
 				// assemble history
diff --git a/packages/core/src/utils/autoFixer.ts b/packages/core/src/utils/autoFixer.ts
index 9e8838e..48b8d81 100644
--- a/packages/core/src/utils/autoFixer.ts
+++ b/packages/core/src/utils/autoFixer.ts
@@ -1,4 +1,7 @@
 import chalk from 'chalk'
+import * as z from 'zod'
+
+import type { PageAgentTool } from '../tools'
 
 /**
  * Normalize LLM response and fix common format issues.
@@ -9,9 +12,10 @@ import chalk from 'chalk'
  * - Arguments wrapped as double JSON string
  * - Nested function call format
  * - Missing action field (fallback to wait)
+ * - Primitive action input for single-field tools (e.g. `{"click_element_by_index": 2}`)
  * - etc.
  */
-export function normalizeResponse(response: any): any {
+export function normalizeResponse(response: any, tools?: Map<string, PageAgentTool>): any {
 	let resolvedArguments = null as any
 
 	const choice = (response as { choices?: Choice[] }).choices?.[0]
@@ -78,6 +82,27 @@ export function normalizeResponse(response: any): any {
 		resolvedArguments.action = safeJsonParse(resolvedArguments.action)
 	}
 
+	// fix primitive action input for single-field tools
+	// e.g. {"click_element_by_index": 2} → {"click_element_by_index": {"index": 2}}
+	if (resolvedArguments.action && tools) {
+		const action = resolvedArguments.action
+		const toolName = Object.keys(action)[0]
+		const value = action[toolName]
+		const schema = toolName && tools.get(toolName)?.inputSchema
+
+		if (schema instanceof z.ZodObject && value !== null && typeof value !== 'object') {
+			const requiredKey = Object.keys(schema.shape).find(
+				(k) => !(schema.shape as Record<string, z.ZodType>)[k].safeParse(undefined).success
+			)
+			if (requiredKey) {
+				console.log(
+					chalk.yellow(`[normalizeResponse] #6: coercing primitive action input for "${toolName}"`)
+				)
+				resolvedArguments.action = { [toolName]: { [requiredKey]: value } }
+			}
+		}
+	}
+
 	// fix incomplete formats
 	if (!resolvedArguments.action) {
 		console.log(chalk.yellow(`[normalizeResponse] #5: fixing tool_call`))