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vercel

Next.js DevTools MCP

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browser_eval

Guides setup and use of agent-browser CLI for automated browser tasks like navigating pages, clicking, and capturing console errors in a real browser.

Instructions

Set up and use browser automation for this project via the agent-browser CLI.

This tool does NOT drive the browser itself. It points you at agent-browser — a fast, native browser-automation CLI built for agents (https://github.com/vercel-labs/agent-browser) — and tells you how to install it (if needed) and where to start. You then run its commands directly (you have shell access), which is faster and more capable than proxying automation through MCP.

Call this when you need to open pages, click, type, screenshot, or capture console errors in a real browser.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
taskNo

Schema Changelog

Changes observed during successful MCP inspections. Dates show when Glama detected each change.

  1. Changed20 schema fields changedv0.4.0
    • removedInput schema / properties / action
      Removed value: -{
-  "description": "The action to perform using browser automation",
-  "enum": [
-    "start",
-    "navigate",
-    "click",
-    "type",
-    "fill_form",
-    "evaluate",
-    "screenshot",
-    "console_messages",
-    "close",
-    "drag",
-    "upload_file",
-    "list_tools"
-  ],
-  "type": "string"
-}
    • removedInput schema / properties / browser
      Removed value: -{
-  "enum": [
-    "chrome",
-    "firefox",
-    "webkit",
-    "msedge"
-  ],
-  "type": "string"
-}
    • removedInput schema / properties / button
      Removed value: -{
-  "enum": [
-    "left",
-    "right",
-    "middle"
-  ],
-  "type": "string"
-}
    • removedInput schema / properties / doubleClick
      Removed value: -{
-  "type": "boolean"
-}
    • removedInput schema / properties / element
      Removed value: -{
-  "type": "string"
-}
    • removedInput schema / properties / endElement
      Removed value: -{
-  "type": "string"
-}
    • removedInput schema / properties / endRef
      Removed value: -{
-  "type": "string"
-}
    • removedInput schema / properties / errorsOnly
      Removed value: -{
-  "type": "boolean"
-}
    • removedInput schema / properties / fields
      Removed value: -{
-  "items": {
-    "properties": {
-      "selector": {
-        "type": "string"
-      },
-      "value": {
-        "type": "string"
-      }
-    },
-    "type": "object"
-  },
-  "type": "array"
-}
    • removedInput schema / properties / files
      Removed value: -{
-  "items": {
-    "type": "string"
-  },
-  "type": "array"
-}
    • removedInput schema / properties / fullPage
      Removed value: -{
-  "type": "boolean"
-}
    • removedInput schema / properties / headless
      Removed value: -{
-  "type": "boolean"
-}
    • removedInput schema / properties / modifiers
      Removed value: -{
-  "items": {
-    "type": "string"
-  },
-  "type": "array"
-}
    • removedInput schema / properties / ref
      Removed value: -{
-  "type": "string"
-}
    • removedInput schema / properties / script
      Removed value: -{
-  "type": "string"
-}
    • removedInput schema / properties / startElement
      Removed value: -{
-  "type": "string"
-}
    • removedInput schema / properties / startRef
      Removed value: -{
-  "type": "string"
-}
    • addedInput schema / properties / task
      Added value: +{
+  "type": "string"
+}
    • removedInput schema / properties / text
      Removed value: -{
-  "type": "string"
-}
    • removedInput schema / properties / url
      Removed value: -{
-  "type": "string"
-}
  2. First observedv0.3.10

TDQS

B3.3/5.0
Behavior3/5

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

No annotations provided, so description carries full burden. It discloses that the tool doesn't drive the browser but points to an external CLI. Lacks details on installation requirements, potential side effects, or system permissions needed, which is a gap for a setup tool.

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 three sentences plus an additional paragraph. It is relatively concise but could be more structured (e.g., separate usage from behavior). No wasted words, but the middle sentence about what it doesn't do could be integrated.

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?

The description covers purpose and usage context but omits parameter details and doesn't explain output or return values. For a simple tool with one optional param and no output schema, the missing parameter guidance is a notable gap.

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

Parameters1/5

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

The input schema has one optional string parameter 'task' with 0% schema description coverage. The description does not explain what 'task' is, how to use it, or what values are expected, leaving the agent with no guidance beyond the 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 it sets up browser automation via agent-browser CLI. It distinguishes from sibling tools (nextjs_*) which are not browser-related. However, it includes a negative statement ('does NOT drive the browser itself') that adds clarity but also could be confusing.

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

Usage Guidelines4/5

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

Explicit usage condition: 'Call this when you need to open pages, click, type, screenshot, or capture console errors in a real browser.' It also notes that direct CLI usage is faster than MCP. No explicit when-not-to or alternatives, but the context is clear.

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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