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Web Screenshot

web_screenshot
Read-only

Captures a PNG screenshot of the current page of a web session (returned inline so web AIs can see it). Useful to ground what the page looks like before acting.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
sessionNoSession name (a named login profile, e.g. 'linkedin'). Defaults to 'default'.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
urlNoURL of the page that was captured.
bytesNoPNG size in bytes (the image itself is an inline content block).

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changed
    • changedOutput schema / (root)
      Previous value: -nullNew value: +{
+  "properties": {
+    "bytes": {
+      "description": "PNG size in bytes (the image itself is an inline content block).",
+      "type": "integer"
+    },
+    "url": {
+      "description": "URL of the page that was captured.",
+      "type": "string"
+    }
+  },
+  "type": "object"
+}
  2. Added

TDQS

A4/5.0
Behavior4/5

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

Annotations already mark it as read-only and non-destructive; the description adds useful behavior by specifying the output is a PNG returned inline so the agent can view it. It does not go into failure behavior, but this is minor for a simple capture tool.

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 worded sentences: the first states what it does and the output form, the second gives the purpose. No filler, and the most important information is front-loaded.

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?

For a one-optional-parameter, read-only tool with a complete schema and output schema, the description gives enough context about output and intended use. It could mention prerequisites like needing an active web session, but this is inferable from the tool family and session parameter.

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, session, is fully described in the schema, including its default and an example. The description adds no parameter information, but the high schema coverage means it does not need to.

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 states a specific action and resource: capturing a PNG screenshot of the current page of a web session, so an agent can understand what it does. It does not explicitly differentiate itself from sibling tools like screenshot_capture, though 'web session' narrows the scope.

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?

It gives a clear context for use ('ground what the page looks like before acting'), which tells the agent when it is appropriate. It does not name alternatives or state when not to use it, such as preferring screenshot_capture for captures outside a web session.

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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