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Browser Session MCP

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Rust
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list_pages

Read-only

Lists a browser session's tabs in stable order and marks the active tab, so you can get current tab indices before switching, closing, or targeting a tab with tabIndex.

Instructions

List the session's tabs in a stable order; it changes nothing. The active tab (the one navigate/evaluate/screenshot/click target by default) is marked with * in the text and active: true in the structured output. Call it before switch_tab, close_tab, or evaluate/profiling with tabIndex, to get a current index; use list_browser_sessions to see sessions rather than tabs, and list_visits for navigation history. Indices stay stable until a tab is closed, after which later tabs shift down one. The list is empty if every tab was closed; the next navigate opens a new one.

Input Schema

NameRequiredDescriptionDefault
sessionIdYesThe id returned by open_browser_session. Errors if no open session has it.

Output Schema

NameRequiredDescriptionDefault
pagesYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv0.1.5
    • changedOutput schema / (root)
      Previous value: -nullNew value: +{
+  "$defs": {
+    "PageSummary": {
+      "properties": {
+        "active": {
+          "description": "Whether this is the tab other tools act on by default.",
+          "type": "boolean"
+        },
+        "index": {
+          "description": "0-based index to pass as `tabIndex`.",
+          "format": "uint",
+          "minimum": 0,
+          "type": "integer"
+        },
+        "title": {
+          "type": "string"
+        },
+        "url": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "index",
+        "url",
+        "title",
+        "active"
+      ],
+      "type": "object"
+    }
+  },
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "properties": {
+    "pages": {
+      "items": {
+        "$ref": "#/$defs/PageSummary"
+      },
+      "type": "array"
+    }
+  },
+  "required": [
+    "pages"
+  ],
+  "type": "object"
+}
  2. Changed1 schema field changed
    • addedInput schema / properties / sessionId / description
      Added value: +"The id returned by open_browser_session. Errors if no open session has it."
  3. First observedv0.1.2

TDQS

A4.7/5.0
Behavior5/5

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

Beyond the readOnlyHint annotation, the description explains stable ordering, active-tab marking, index stability, index shifting after a tab close, the empty-list state, and that a subsequent navigate opens a new tab. These details materially affect how an agent should interpret and use the returned list.

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?

The description is front-loaded with the core action and is dense with useful operational detail. Every sentence contributes either purpose, usage routing, active-tab semantics, or index behavior, without redundant filler.

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

Completeness5/5

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

Given the single required parameter, complete schema coverage, existing output schema, and read-only annotations, the description covers the remaining behavioral questions: ordering, active-tab identification, index stability, empty-state behavior, and when to choose this tool over siblings. Nothing essential for correct invocation appears missing.

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?

The only parameter is sessionId, and the schema already provides a complete description of it, including that it comes from open_browser_session and errors if no open session matches. The description does not add further parameter-level meaning, so the high schema coverage supports a baseline score of 3.

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?

The description begins with a specific verb and resource: 'List the session's tabs in a stable order.' It also distinguishes this tool from session listing and visit-history listing by explicitly naming list_browser_sessions and list_visits as different resources.

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

Usage Guidelines5/5

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

It gives explicit call conditions: use it before switch_tab, close_tab, or evaluate/profiling with tabIndex to get a current index. It also names alternatives for different needs, directing agents to list_browser_sessions for sessions and list_visits for navigation history.

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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