diff --git a/tracers.ts/src/commander/index.ts b/tracers.ts/src/commander/index.ts
index 365fbc1..ff0e4c6 100644
--- a/tracers.ts/src/commander/index.ts
+++ b/tracers.ts/src/commander/index.ts
@@ -21,6 +21,6 @@ export class Commander {
   }
 
   public output() {
-    return this.commands;
+    return JSON.stringify(this.commands);
   }
 }
diff --git a/tracers.ts/src/tracer/array-tracer.ts b/tracers.ts/src/tracer/array-tracer.ts
index f121b53..e7f37ce 100644
--- a/tracers.ts/src/tracer/array-tracer.ts
+++ b/tracers.ts/src/tracer/array-tracer.ts
@@ -20,7 +20,7 @@ export class ArrayTracer<T> {
     commander.command({
       action: "define",
       tracer: null,
-      params: {
+      payload: {
         type: "ArrayTracer",
         id: arrayTracer.tracerId,
         desc: option.description,
@@ -34,7 +34,7 @@ export class ArrayTracer<T> {
     commander.command({
       action: "preset",
       tracer: this.tracerId,
-      params: array,
+      payload: array,
     });
   }
 
@@ -43,7 +43,7 @@ export class ArrayTracer<T> {
     commander.command({
       action: "extend",
       tracer: this.tracerId,
-      params: { size },
+      payload: { size },
     });
   }
 
@@ -52,7 +52,7 @@ export class ArrayTracer<T> {
     commander.command({
       action: "shrink",
       tracer: this.tracerId,
-      params: { size },
+      payload: { size },
     });
   }
 
@@ -61,7 +61,7 @@ export class ArrayTracer<T> {
     commander.command({
       action: "pick",
       tracer: this.tracerId,
-      params: { index },
+      payload: { index },
     });
   }
 
@@ -70,7 +70,7 @@ export class ArrayTracer<T> {
     commander.command({
       action: "drop",
       tracer: this.tracerId,
-      params: { index },
+      payload: { index },
     });
   }
 
@@ -79,7 +79,7 @@ export class ArrayTracer<T> {
     commander.command({
       action: "patch",
       tracer: this.tracerId,
-      params: { index, value },
+      payload: { index, value },
     });
   }
 
@@ -88,7 +88,7 @@ export class ArrayTracer<T> {
     commander.command({
       action: "reset",
       tracer: this.tracerId,
-      params: { index },
+      payload: { index },
     });
   }
 }
diff --git a/tracers.ts/src/types/command/array-tracer-command.ts b/tracers.ts/src/types/command/array-tracer-command.ts
index 1662d42..f0a892c 100644
--- a/tracers.ts/src/types/command/array-tracer-command.ts
+++ b/tracers.ts/src/types/command/array-tracer-command.ts
@@ -1,49 +1,49 @@
 export type ArrayTracerDefineCommand = {
   action: "define";
   tracer: null;
-  params: { type: "ArrayTracer"; id: string; desc?: string };
+  payload: { type: "ArrayTracer"; id: string; desc?: string };
 };
 
 export type ArrayTracerPresetCommand<T = unknown> = {
   action: "preset";
   tracer: string;
-  params: T[];
+  payload: T[];
 };
 
 export type ArrayTracerExtendCommand = {
   action: "extend";
   tracer: string;
-  params: { size: number };
+  payload: { size: number };
 };
 
 export type ArrayTracerShrinkCommand = {
   action: "shrink";
   tracer: string;
-  params: { size: number };
+  payload: { size: number };
 };
 
 export type ArrayTracerPickCommand = {
   action: "pick";
   tracer: string;
-  params: { index: number };
+  payload: { index: number };
 };
 
 export type ArrayTracerDropCommand = {
   action: "drop";
   tracer: string;
-  params: { index: number };
+  payload: { index: number };
 };
 
 export type ArrayTracerPatchCommand<T = unknown> = {
   action: "patch";
   tracer: string;
-  params: { index: number; value: T };
+  payload: { index: number; value: T };
 };
 
 export type ArrayTracerResetCommand = {
   action: "reset";
   tracer: string;
-  params: { index: number };
+  payload: { index: number };
 };
 
 export type ArrayTracerCommand<T = never> =
diff --git a/tracers.ts/src/types/tracer/index.ts b/tracers.ts/src/types/tracer/index.ts
index 5787464..610e992 100644
--- a/tracers.ts/src/types/tracer/index.ts
+++ b/tracers.ts/src/types/tracer/index.ts
@@ -1,5 +1,5 @@
 import type { ArrayTracerDefineCommand } from "../command";
 
-type ArrayTracer = ArrayTracerDefineCommand["params"]["type"];
+type ArrayTracer = ArrayTracerDefineCommand["payload"]["type"];
 
 export type TracerType = ArrayTracer;