web-ui-tester

List page and DevTools tools

browser_list_tools

Read-only

Lists available WebMCP and DevTools tools for a session, enabling agents to inspect schemas and call them against the current page.

Instructions

Lists tools beyond this server's own that can run against the session's page, by qualified name: "webmcp." for tools the site itself publishes through WebMCP (read live — they change as the page navigates), and "devtools." for chrome-devtools-mcp's tools (performance traces, Lighthouse, emulation, heap snapshots…), which this server runs for you — no extra MCP server to configure. Follow with browser_tool_schema, then browser_call_tool.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "sessionId": "<sessionId>"
    },
    "name": "browser_list_tools"
  }
}

Input Schema

Name	Required	Description	Default
`source`	No	Which tools to list. Defaults to all.
`sessionId`	Yes	Session id returned by browser_start.

Schema Changelog

Changes observed during successful MCP inspections.

AddedSep 30, 2026

TDQS

A4.3/5.0

Behavior4/5

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds genuinely new behavioral context: webmcp tools are read live and change as the page navigates, and devtools tools are executed by this server with no separate MCP server to configure. It does not describe the shape or volume of the returned list, which is a minor gap.

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?

Front-loaded with the verb and resource, then a compact closing instruction about the follow-up calls. Dense but every clause carries information; the em-dash parenthetical about devtools capabilities is the one place it sprawls slightly.

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 no output schema, the description carries the burden of describing returns and does so by giving the qualified-name formats and noting that webmcp results are volatile as the page navigates. It does not say whether results are paginated, bounded, or error-prone when no page is loaded, leaving a small completeness gap for a 2-parameter, session-scoped listing tool.

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

Parameters4/5

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

Schema description coverage is 100%, so the baseline is 3 and the schema already documents sessionId and the source enum. The description nevertheless adds meaning by explaining what the webmcp and devtools categories actually contain, which is the semantic key to choosing a source filter value.

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

Purpose5/5

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

States a specific verb and resource — listing tools that run against the session's page — and partitions the result into two clearly named namespaces, "webmcp.<name>" versus "devtools.<name>". It further differentiates itself from the sibling tools it feeds into (browser_tool_schema, browser_call_tool), so an agent can place it precisely in the tool landscape.

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?

Lays out an explicit call sequence — list here, then browser_tool_schema, then browser_call_tool — which tells the agent when this tool belongs in a workflow. It stops short of saying when not to use it or how it relates to the similarly named sibling browser_list, so the guidance is strong but not complete.

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