web-debug-mcp

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Set JavaScript breakpoint

web_breakpoint_set

Set a breakpoint using one-based source coordinates. Select coordinateSpace=original and an exact source URL/scriptId from the sources capture to translate a source map; ambiguous or unavailable mappings fail explicitly.

Instructions

Input Schema

Name	Required	Default
`line`	Yes
`column`	No
`scriptId`	No
`sessionId`	Yes
`sourceUrl`	Yes
`coordinateSpace`	No	generated

Output Schema

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

Schema Changelog

Changes observed during successful MCP inspections.

Changed7 schema fields changedv0.12.0Oct 15, 2026

addedInput schema / properties / coordinateSpace

Added value: +{
+  "default": "generated",
+  "enum": [
+    "generated",
+    "original"
+  ],
+  "type": "string"
+}

addedInput schema / properties / scriptId

Added value: +{
+  "maxLength": 100,
+  "minLength": 1,
+  "type": "string"
+}

addedOutput schema / definitions / SourceLocationOutput

Added value: +{
+  "additionalProperties": false,
+  "properties": {
+    "column": {
+      "exclusiveMinimum": 0,
+      "maximum": 9007199254740991,
+      "type": "integer"
+    },
+    "line": {
+      "exclusiveMinimum": 0,
+      "maximum": 9007199254740991,
+      "type": "integer"
+    },
+    "url": {
+      "maxLength": 2560,
+      "type": "string"
+    }
+  },
+  "required": [
+    "url",
+    "line",
+    "column"
+  ],
+  "type": "object"
+}

addedOutput schema / properties / data / properties / coordinateSpace

Added value: +{
+  "enum": [
+    "generated",
+    "original"
+  ],
+  "type": "string"
+}

addedOutput schema / properties / data / properties / resolved

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

addedOutput schema / properties / data / properties / scriptId

Added value: +{
+  "maxLength": 100,
+  "type": "string"
+}

addedOutput schema / properties / data / properties / status

Added value: +{
+  "enum": [
+    "resolved",
+    "stale"
+  ],
+  "type": "string"
+}

Changed7 schema fields changedv0.7.0Sep 1, 2026

removedOutput schema / definitions / __schema1

Removed value: -{
-  "anyOf": [
-    {
-      "type": "string"
-    },
-    {
-      "type": "number"
-    },
-    {
-      "type": "boolean"
-    },
-    {
-      "type": "null"
-    },
-    {
-      "items": {
-        "$ref": "#/definitions/__schema1"
-      },
-      "type": "array"
-    },
-    {
-      "additionalProperties": {
-        "$ref": "#/definitions/__schema1"
-      },
-      "propertyNames": {
-        "type": "string"
-      },
-      "type": "object"
-    }
-  ]
-}

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: +{
+  "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"
+  }
+}

addedOutput schema / properties / data / required

Added value: +[
+  "id",
+  "sourceUrl",
+  "line",
+  "column"
+]

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

changedOutput schema / properties / error / properties / details / allOf

Previous value: -[
-  {
-    "$ref": "#/definitions/__schema1"
-  }
-]New value: +[
+  {
+    "$ref": "#/definitions/__schema0"
+  }
+]

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

TDQS

A3.8/5.0

Behavior4/5

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

Annotations cover the safety profile (not read-only, not destructive, not idempotent, open-world), lowering the bar. The description adds real behavioral context beyond them: coordinates are one-based, translation only occurs with original space plus an exact URL/scriptId, and ambiguous or unavailable mappings fail explicitly rather than silently.

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

Conciseness5/5

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

Two tightly packed sentences, front-loaded with the coordinate convention and failure semantics. Every clause carries information; nothing is redundant with the title or schema.

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

Completeness4/5

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

With an output schema present, return values need not be described. The definition covers coordinate space, source-map translation, and failure behavior, which is most of what an agent needs. The residual gap is the unmentioned sessionId and the sourceUrl-vs-scriptId selection rule.

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

Parameters3/5

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

Schema description coverage is 0% across 6 parameters, so the description must carry the load. It meaningfully explains coordinateSpace (generated vs original, source-map translation) and the one-based line/column convention, but leaves sessionId unexplained and does not clarify which of sourceUrl/scriptId is preferred.

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?

States a specific verb+resource ('Set a breakpoint') and adds the coordinate semantics, so the agent knows precisely what operation is performed. It does not, however, name or distinguish itself from nearby siblings like web_replay_seek or web_debug_control.

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?

It gives a conditional for one mode ('Select coordinateSpace=original ... to translate a source map'), which is genuine usage guidance for a parameter path. But it never states when to reach for this tool at all versus the other debug/replay tools, so the tool-selection guidance is only implied.

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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