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nodriver-mcp-server

by andresolbach
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Python
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Block resource types

block_resources
Idempotent

Block images, fonts, stylesheets, or media in the selected tab to reduce page weight and speed up scraping. Use it to cut bandwidth costs on media-heavy pages while keeping text extraction reliable.

Instructions

Block images, fonts, stylesheets or media to speed up page loads.

Removes most of the bytes on a media-heavy page, which makes scraping several times faster and far cheaper over a metered or proxied connection.

Blocking stylesheets breaks layout, so anything that depends on element geometry becomes unreliable — click_at, element screenshots, and the visible check in wait_for_selector. Text extraction is unaffected.

Requests are matched on the resource type Chrome reports for them, so an asset served from an extension-less URL is still blocked, and blocking one type never catches another.

Applies to ONE TAB — the selected page — and stays in effect there across navigations until called again with no types. A tab opened afterwards with new_page starts unblocked and needs its own call.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
typesNoResource types to block. ["image", "font", "media"] is the usual choice for scraping — it keeps stylesheets, so layout-dependent behaviour still works. Pass an empty list or omit to unblock everything.
browserNoWhich browser to act on. Each name is an independent Chrome, created on first use. Omit for the shared default; parallel agents each need their own name.default

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
resultYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv2.5.0
    • addedInput schema / properties / browser
      Added value: +{
+  "default": "default",
+  "description": "Which browser to act on. Each name is an independent Chrome, created on first use. Omit for the shared default; parallel agents each need their own name.",
+  "type": "string"
+}
  2. First observedv1.7.2

TDQS

A4.9/5.0
Behavior5/5

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

Annotations provide idempotentHint=true and destructiveHint=false but the description goes far beyond them: it discloses that blocking stylesheets breaks layout-dependent operations, that matching follows Chrome-reported resource types (so extension-less URLs are still caught and types never cross-match), and that the effect is scoped to one tab and resets on new_page. No contradiction with annotations — idempotency and reversibility are consistent with 'call again with no types to unblock.'

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?

Four paragraphs, but every sentence earns its place and the structure is logical: purpose/benefit → side effects → matching semantics → scope/persistence. The most important claim (what it blocks, why) is front-loaded, and the longer sections address genuinely non-obvious behavior that an agent must know before calling.

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?

For a tool with subtle side effects and scoping, the description covers everything: purpose, benefit, what breaks and what doesn't, matching semantics, persistence across navigations, how to unblock, and the new_page reset. An output schema exists, so return-value explanation isn't required. Nothing an agent needs to invoke it correctly is missing.

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 coverage is 100% and both parameter descriptions are excellent: `types` documents the enum values, the recommended scraping combination, and the unblock behavior; `browser` explains the per-agent isolation. Baseline is 3 given full coverage, but the description adds value by clarifying matching semantics (Chrome-reported type, no cross-type matching) that enriches how `types` should be understood. Not a 5 because the core parameter meaning lives in the schema, not the description.

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 opens with a specific verb+resource ('Block images, fonts, stylesheets or media') and a concrete purpose ('speed up page loads'). No sibling tool performs this action — the closest (bypass_insecure_warning, cf_verify, set_browser_flags) are all distinct — so the tool is clearly differentiated without needing to name a sibling.

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?

The description gives explicit when-to-use guidance (speed up scraping on media-heavy pages), explicit exclusions ('Blocking stylesheets breaks layout... click_at, element screenshots, and the `visible` check in wait_for_selector become unreliable'), and what is unaffected ('Text extraction is unaffected'). The schema description reinforces this with a recommended combination. Scope (single tab, persists across navigations, new_page starts unblocked) is also spelled out. This is full usage routing with no inference required.

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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