web-debug-mcp

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Control paused JavaScript debugger

web_debug_control

Destructive

Resume or step through a paused JavaScript execution to control debugging flow. Select an action to continue, step over, step into, or step out of the current breakpoint.

Instructions

Resume or step a paused local JavaScript target.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`action`	Yes
`sessionId`	Yes

Output Schema

TableJSON Schema

Name	Required	Description	Default
`ok`	Yes
`data`	No
`error`	No
`warnings`	Yes
`artifacts`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed8 schema fields changedv0.10.0Sep 8, 2026

addedOutput schema / definitions / DebuggerSnapshotOutput

Added value: +{
+  "additionalProperties": false,
+  "properties": {
+    "breakpoints": {
+      "items": {
+        "additionalProperties": false,
+        "properties": {
+          "column": {
+            "anyOf": [
+              {
+                "maximum": 9007199254740991,
+                "minimum": -9007199254740991,
+                "type": "integer"
+              },
+              {
+                "type": "null"
+              }
+            ]
+          },
+          "id": {
+            "maxLength": 500,
+            "type": "string"
+          },
+          "line": {
+            "maximum": 9007199254740991,
+            "minimum": -9007199254740991,
+            "type": "integer"
+          },
+          "sourceUrl": {
+            "maxLength": 2560,
+            "type": "string"
+          }
+        },
+        "required": [
+          "id",
+          "sourceUrl",
+          "line",
+          "column"
+        ],
+        "type": "object"
+      },
+      "maxItems": 100,
+      "type": "array"
+    },
+    "callFrames": {
+      "items": {
+        "additionalProperties": false,
+        "properties": {
+          "column": {
+            "maximum": 9007199254740991,
+            "minimum": -9007199254740991,
+            "type": "integer"
+          },
+          "functionName": {
+            "maxLength": 500,
+            "type": "string"
+          },
+          "line": {
+            "maximum": 9007199254740991,
+            "minimum": -9007199254740991,
+            "type": "integer"
+          },
+          "locals": {
+            "additionalProperties": {
+              "$ref": "#/definitions/JsonValue"
+            },
+            "propertyNames": {
+              "type": "string"
+            },
+            "type": "object"
+          },
+          "scopeNames": {
+            "items": {
+              "maxLength": 100,
+              "type": "string"
+            },
+            "maxItems": 50,
+            "type": "array"
+          },
+          "url": {
+            "maxLength": 2560,
+            "type": "string"
+          }
+        },
+        "required": [
+          "functionName",
+          "url",
+          "line",
+          "column",
+          "scopeNames",
+          "locals"
+        ],
+        "type": "object"
+      },
+      "maxItems": 50,
+      "type": "array"
+    },
+    "paused": {
+      "type": "boolean"
+    },
+    "reason": {
+      "anyOf": [
+        {
+          "maxLength": 500,
+          "type": "string"
+        },
+        {
+          "type": "null"
+        }
+      ]
+    }
+  },
+  "required": [
+    "paused",
+    "reason",
+    "callFrames",
+    "breakpoints"
+  ],
+  "type": "object"
+}

addedOutput schema / definitions / JsonValue

Added value: +{
+  "allOf": [
+    {
+      "$ref": "#/definitions/__schema0"
+    }
+  ]
+}

changedOutput schema / definitions / __schema0 / anyOf

Previous value: -[
-  {
-    "type": "string"
-  },
-  {
-    "type": "number"
-  },
-  {
-    "type": "boolean"
-  },
-  {
-    "type": "null"
-  },
-  {
-    "items": {
-      "$ref": "#/definitions/__schema0"
-    },
-    "type": "array"
-  },
-  {
-    "additionalProperties": {
-      "$ref": "#/definitions/__schema0"
-    },
-    "propertyNames": {
-      "type": "string"
-    },
-    "type": "object"
-  }
-]New value: +[
+  {
+    "type": "string"
+  },
+  {
+    "type": "number"
+  },
+  {
+    "type": "boolean"
+  },
+  {
+    "type": "null"
+  },
+  {
+    "items": {
+      "allOf": [
+        {
+          "$ref": "#/definitions/__schema0"
+        }
+      ]
+    },
+    "type": "array"
+  },
+  {
+    "additionalProperties": {
+      "allOf": [
+        {
+          "$ref": "#/definitions/__schema0"
+        }
+      ]
+    },
+    "propertyNames": {
+      "type": "string"
+    },
+    "type": "object"
+  }
+]

removedOutput schema / properties / data / additionalProperties
```
Removed value: -false
```

addedOutput schema / properties / data / allOf

Added value: +[
+  {
+    "$ref": "#/definitions/DebuggerSnapshotOutput"
+  }
+]

removedOutput schema / properties / data / properties

Removed value: -{
-  "breakpoints": {
-    "items": {
-      "additionalProperties": false,
-      "properties": {
-        "column": {
-          "anyOf": [
-            {
-              "maximum": 9007199254740991,
-              "minimum": -9007199254740991,
-              "type": "integer"
-            },
-            {
-              "type": "null"
-            }
-          ]
-        },
-        "id": {
-          "maxLength": 500,
-          "type": "string"
-        },
-        "line": {
-          "maximum": 9007199254740991,
-          "minimum": -9007199254740991,
-          "type": "integer"
-        },
-        "sourceUrl": {
-          "maxLength": 2560,
-          "type": "string"
-        }
-      },
-      "required": [
-        "id",
-        "sourceUrl",
-        "line",
-        "column"
-      ],
-      "type": "object"
-    },
-    "maxItems": 100,
-    "type": "array"
-  },
-  "callFrames": {
-    "items": {
-      "additionalProperties": false,
-      "properties": {
-        "column": {
-          "maximum": 9007199254740991,
-          "minimum": -9007199254740991,
-          "type": "integer"
-        },
-        "functionName": {
-          "maxLength": 500,
-          "type": "string"
-        },
-        "line": {
-          "maximum": 9007199254740991,
-          "minimum": -9007199254740991,
-          "type": "integer"
-        },
-        "locals": {
-          "additionalProperties": {
-            "$ref": "#/definitions/__schema0"
-          },
-          "propertyNames": {
-            "type": "string"
-          },
-          "type": "object"
-        },
-        "scopeNames": {
-          "items": {
-            "maxLength": 100,
-            "type": "string"
-          },
-          "maxItems": 50,
-          "type": "array"
-        },
-        "url": {
-          "maxLength": 2560,
-          "type": "string"
-        }
-      },
-      "required": [
-        "functionName",
-        "url",
-        "line",
-        "column",
-        "scopeNames",
-        "locals"
-      ],
-      "type": "object"
-    },
-    "maxItems": 50,
-    "type": "array"
-  },
-  "paused": {
-    "type": "boolean"
-  },
-  "reason": {
-    "anyOf": [
-      {
-        "maxLength": 500,
-        "type": "string"
-      },
-      {
-        "type": "null"
-      }
-    ]
-  }
-}

removedOutput schema / properties / data / required

Removed value: -[
-  "paused",
-  "reason",
-  "callFrames",
-  "breakpoints"
-]

removedOutput schema / properties / data / type
```
Removed value: -"object"
```

Changed5 schema fields changedv0.7.0Sep 1, 2026

addedOutput schema / properties / data / additionalProperties
```
Added value: +false
```

removedOutput schema / properties / data / allOf

Removed value: -[
-  {
-    "$ref": "#/definitions/__schema0"
-  }
-]

addedOutput schema / properties / data / properties

Added value: +{
+  "breakpoints": {
+    "items": {
+      "additionalProperties": false,
+      "properties": {
+        "column": {
+          "anyOf": [
+            {
+              "maximum": 9007199254740991,
+              "minimum": -9007199254740991,
+              "type": "integer"
+            },
+            {
+              "type": "null"
+            }
+          ]
+        },
+        "id": {
+          "maxLength": 500,
+          "type": "string"
+        },
+        "line": {
+          "maximum": 9007199254740991,
+          "minimum": -9007199254740991,
+          "type": "integer"
+        },
+        "sourceUrl": {
+          "maxLength": 2560,
+          "type": "string"
+        }
+      },
+      "required": [
+        "id",
+        "sourceUrl",
+        "line",
+        "column"
+      ],
+      "type": "object"
+    },
+    "maxItems": 100,
+    "type": "array"
+  },
+  "callFrames": {
+    "items": {
+      "additionalProperties": false,
+      "properties": {
+        "column": {
+          "maximum": 9007199254740991,
+          "minimum": -9007199254740991,
+          "type": "integer"
+        },
+        "functionName": {
+          "maxLength": 500,
+          "type": "string"
+        },
+        "line": {
+          "maximum": 9007199254740991,
+          "minimum": -9007199254740991,
+          "type": "integer"
+        },
+        "locals": {
+          "additionalProperties": {
+            "$ref": "#/definitions/__schema0"
+          },
+          "propertyNames": {
+            "type": "string"
+          },
+          "type": "object"
+        },
+        "scopeNames": {
+          "items": {
+            "maxLength": 100,
+            "type": "string"
+          },
+          "maxItems": 50,
+          "type": "array"
+        },
+        "url": {
+          "maxLength": 2560,
+          "type": "string"
+        }
+      },
+      "required": [
+        "functionName",
+        "url",
+        "line",
+        "column",
+        "scopeNames",
+        "locals"
+      ],
+      "type": "object"
+    },
+    "maxItems": 50,
+    "type": "array"
+  },
+  "paused": {
+    "type": "boolean"
+  },
+  "reason": {
+    "anyOf": [
+      {
+        "maxLength": 500,
+        "type": "string"
+      },
+      {
+        "type": "null"
+      }
+    ]
+  }
+}

addedOutput schema / properties / data / required

Added value: +[
+  "paused",
+  "reason",
+  "callFrames",
+  "breakpoints"
+]

addedOutput schema / properties / data / type
```
Added value: +"object"
```

First observedv0.5.0-next.0Aug 30, 2026

TDQS

B3/5.0

Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare destructiveHint=true and readOnlyHint=false, so the safety profile is known. The description adds only that the target is 'paused' and 'local', but it doesn't disclose behavioral consequences such as execution continuing, side effects from stepping, or whether the session state is modified. It does not contradict the annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single clear sentence with no wasted words, front-loading the core action. It is concise and easy to parse, though it could have added a brief usage note without becoming bloated.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple two-parameter tool with an output schema and clear enum values, the description is minimally adequate. It identifies the resource and action, but it lacks guidance on sessionId sourcing, preconditions, and what happens after each step action. Given the low schema coverage and sibling context, a bit more context would make it fully self-sufficient.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters2/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0%, so the description carries the burden of explaining the parameters. It doesn't mention sessionId at all, and while the action enum values are somewhat self-explanatory, the description doesn't clarify how to choose among resume, stepOver, stepInto, or stepOut. The description adds minimal value beyond the raw schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states a specific verb ('Resume or step') and a specific resource ('a paused local JavaScript target'). It distinguishes the action from inspection-oriented siblings like web_debug_evaluate. However, it doesn't explicitly differentiate itself from other debugger control tools such as web_breakpoint_set or web_replay_seek.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The phrase 'paused local JavaScript target' gives useful context that this tool is for paused debugger sessions. However, it provides no explicit when-to-use or when-not-to-use guidance, and it doesn't name alternatives among the sibling tools, leaving the agent to infer the appropriate usage context.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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