diff --git a/src/api/providers/__tests__/gemini.spec.ts b/src/api/providers/__tests__/gemini.spec.ts
index 8c2ee87a78..84cfe42f37 100644
--- a/src/api/providers/__tests__/gemini.spec.ts
+++ b/src/api/providers/__tests__/gemini.spec.ts
@@ -274,6 +274,19 @@ describe("GeminiHandler", () => {
 					modelId: GEMINI_MODEL_NAME,
 					operation: "createMessage",
 				}),
+				// Verify diagnostic properties are included
+				expect.objectContaining({
+					messageCount: expect.any(Number),
+					geminiContentsCount: expect.any(Number),
+					hasToolUseBlocks: expect.any(Boolean),
+					hasToolResultBlocks: expect.any(Boolean),
+					hasImageBlocks: expect.any(Boolean),
+					emptyPartsCount: expect.any(Number),
+					toolIdToNameSize: expect.any(Number),
+					hasThinkingConfig: expect.any(Boolean),
+					usingNativeTools: expect.any(Boolean),
+					includeThoughtSignatures: expect.any(Boolean),
+				}),
 			)
 
 			// Verify it's an ApiProviderError
diff --git a/src/api/providers/gemini.ts b/src/api/providers/gemini.ts
index 1cc9228256..0681992101 100644
--- a/src/api/providers/gemini.ts
+++ b/src/api/providers/gemini.ts
@@ -335,7 +335,36 @@ export class GeminiHandler extends BaseProvider implements SingleCompletionHandl
 		} catch (error) {
 			const errorMessage = error instanceof Error ? error.message : String(error)
 			const apiError = new ApiProviderError(errorMessage, this.providerName, model, "createMessage")
-			TelemetryService.instance.captureException(apiError)
+
+			// Add request diagnostics to help debug INVALID_ARGUMENT errors
+			TelemetryService.instance.captureException(apiError, {
+				// Message structure diagnostics
+				messageCount: messages.length,
+				geminiContentsCount: contents.length,
+
+				// Content type diagnostics
+				hasToolUseBlocks: messages.some(
+					(m) => Array.isArray(m.content) && m.content.some((b: { type: string }) => b.type === "tool_use"),
+				),
+				hasToolResultBlocks: messages.some(
+					(m) =>
+						Array.isArray(m.content) && m.content.some((b: { type: string }) => b.type === "tool_result"),
+				),
+				hasImageBlocks: messages.some(
+					(m) => Array.isArray(m.content) && m.content.some((b: { type: string }) => b.type === "image"),
+				),
+
+				// Conversion diagnostics - check for empty parts which cause INVALID_ARGUMENT
+				emptyPartsCount: contents.filter((c) => !c.parts || c.parts.length === 0).length,
+
+				// Tool mapping diagnostics - incomplete mapping causes conversion errors
+				toolIdToNameSize: toolIdToName.size,
+
+				// Configuration that might affect the request
+				hasThinkingConfig: Boolean(thinkingConfig),
+				usingNativeTools,
+				includeThoughtSignatures,
+			})
 
 			if (error instanceof Error) {
 				throw new Error(t("common:errors.gemini.generate_stream", { error: error.message }))