feat: Add experimental malformed JSON repair for tool calls

packages/types/src/experiment.ts

@@ -14,6 +14,7 @@ export const experimentIds = [
 	"runSlashCommand",
 	"multipleNativeToolCalls",
 	"customTools",
+	"malformedJsonRepair",
 ] as const
 
 export const experimentIdsSchema = z.enum(experimentIds)
@@ -32,6 +33,11 @@ export const experimentsSchema = z.object({
 	runSlashCommand: z.boolean().optional(),
 	multipleNativeToolCalls: z.boolean().optional(),
 	customTools: z.boolean().optional(),
+	/**
+	 * Enable automatic repair of malformed JSON in LLM tool call responses.
+	 * Useful for models like Grok that struggle with strict JSON formatting.
+	 */
+	malformedJsonRepair: z.boolean().optional(),
 })
 
 export type Experiments = z.infer<typeof experimentsSchema>

src/core/assistant-message/NativeToolCallParser.ts

@@ -3,6 +3,9 @@ import { parseJSON } from "partial-json"
 import { type ToolName, toolNames, type FileEntry } from "@roo-code/types"
 import { customToolRegistry } from "@roo-code/core"
 
+import { repairJson } from "../../utils/json-repair"
+import { logger } from "../../utils/logging"
+
 import {
 	type ToolUse,
 	type McpToolUse,
@@ -51,6 +54,25 @@ export type ToolCallStreamEvent = ApiStreamToolCallStartChunk | ApiStreamToolCal
  * provider-level raw chunks into start/delta/end events.
  */
 export class NativeToolCallParser {
+	// Configuration for malformed JSON repair (experimental feature)
+	private static malformedJsonRepairEnabled = false
+
+	/**
+	 * Enable or disable malformed JSON repair.
+	 * When enabled, the parser will attempt to repair malformed JSON
+	 * in tool call arguments before parsing.
+	 */
+	public static setMalformedJsonRepairEnabled(enabled: boolean): void {
+		this.malformedJsonRepairEnabled = enabled
+	}
+
+	/**
+	 * Check if malformed JSON repair is enabled.
+	 */
+	public static isMalformedJsonRepairEnabled(): boolean {
+		return this.malformedJsonRepairEnabled
+	}
+
 	// Streaming state management for argument accumulation (keyed by tool call id)
 	// Note: name is string to accommodate dynamic MCP tools (mcp_serverName_toolName)
 	private static streamingToolCalls = new Map<
@@ -593,7 +615,29 @@ export class NativeToolCallParser {
 
 		try {
 			// Parse the arguments JSON string
-			const args = toolCall.arguments === "" ? {} : JSON.parse(toolCall.arguments)
+			// If malformed JSON repair is enabled, attempt to repair before parsing
+			let args: Record<string, unknown>
+			if (toolCall.arguments === "") {
+				args = {}
+			} else {
+				try {
+					args = JSON.parse(toolCall.arguments)
+				} catch (parseError) {
+					// JSON parsing failed - attempt repair if enabled
+					if (this.malformedJsonRepairEnabled) {
+						const repaired = repairJson(toolCall.arguments)
+						if (repaired) {
+							logger.info(`[NativeToolCallParser] Repaired malformed JSON for tool ${toolCall.name}`)
+							args = JSON.parse(repaired)
+						} else {
+							// Repair failed, re-throw original error
+							throw parseError
+						}
+					} else {
+						throw parseError
+					}
+				}
+			}
 
 			// Build legacy params object for backward compatibility with XML protocol and UI.
 			// Native execution path uses nativeArgs instead, which has proper typing.

src/core/task/Task.ts

@@ -541,6 +541,16 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 			})
 		}
 
+		// Check malformed JSON repair experiment asynchronously.
+		// This enables repair of malformed JSON in tool call arguments from models like Grok.
+		provider.getState().then((state) => {
+			const isMalformedJsonRepairEnabled = experiments.isEnabled(
+				state.experiments ?? {},
+				EXPERIMENT_IDS.MALFORMED_JSON_REPAIR,
+			)
+			NativeToolCallParser.setMalformedJsonRepairEnabled(isMalformedJsonRepairEnabled)
+		})
+
 		this.toolRepetitionDetector = new ToolRepetitionDetector(this.consecutiveMistakeLimit)
 
 		// Initialize todo list if provided

src/package.json

@@ -466,6 +466,7 @@
 		"i18next": "^25.0.0",
 		"ignore": "^7.0.3",
 		"isbinaryfile": "^5.0.2",
+		"jsonrepair": "^3.13.1",
 		"jwt-decode": "^4.0.0",
 		"lodash.debounce": "^4.0.8",
 		"mammoth": "^1.9.1",

src/shared/__tests__/experiments.spec.ts

@@ -33,6 +33,7 @@ describe("experiments", () => {
 				runSlashCommand: false,
 				multipleNativeToolCalls: false,
 				customTools: false,
+				malformedJsonRepair: false,
 			}
 			expect(Experiments.isEnabled(experiments, EXPERIMENT_IDS.POWER_STEERING)).toBe(false)
 		})
@@ -46,6 +47,7 @@ describe("experiments", () => {
 				runSlashCommand: false,
 				multipleNativeToolCalls: false,
 				customTools: false,
+				malformedJsonRepair: false,
 			}
 			expect(Experiments.isEnabled(experiments, EXPERIMENT_IDS.POWER_STEERING)).toBe(true)
 		})
@@ -59,6 +61,7 @@ describe("experiments", () => {
 				runSlashCommand: false,
 				multipleNativeToolCalls: false,
 				customTools: false,
+				malformedJsonRepair: false,
 			}
 			expect(Experiments.isEnabled(experiments, EXPERIMENT_IDS.POWER_STEERING)).toBe(false)
 		})

src/shared/experiments.ts

@@ -8,6 +8,7 @@ export const EXPERIMENT_IDS = {
 	RUN_SLASH_COMMAND: "runSlashCommand",
 	MULTIPLE_NATIVE_TOOL_CALLS: "multipleNativeToolCalls",
 	CUSTOM_TOOLS: "customTools",
+	MALFORMED_JSON_REPAIR: "malformedJsonRepair",
 } as const satisfies Record<string, ExperimentId>
 
 type _AssertExperimentIds = AssertEqual<Equals<ExperimentId, Values<typeof EXPERIMENT_IDS>>>
@@ -26,6 +27,7 @@ export const experimentConfigsMap: Record<ExperimentKey, ExperimentConfig> = {
 	RUN_SLASH_COMMAND: { enabled: false },
 	MULTIPLE_NATIVE_TOOL_CALLS: { enabled: false },
 	CUSTOM_TOOLS: { enabled: false },
+	MALFORMED_JSON_REPAIR: { enabled: false },
 }
 
 export const experimentDefault = Object.fromEntries(