Set the viewport size in CSS pixels for every tab, including tabs opened later, so snapshots and screenshots use that size.
Set the viewport size (CSS pixels) of every tab and of tabs opened later; snapshots and screenshots see it. For a tall page, browser_screenshot with full_page.
| Name | Required | Description | Default |
|---|---|---|---|
| width | Yes | CSS pixels | |
| height | Yes | CSS pixels |
Changes observed during successful MCP inspections.
v0.7.1Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=false and openWorldHint=true, so the safety profile is covered. The description earns credit for disclosing a real behavioral trait beyond that: the size applies to all existing tabs and future tabs, and affects what snapshots/screenshots capture. It stops short of saying what gets destroyed or reset (e.g., whether per-tab overrides exist).
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two compact sentences with the core behavior front-loaded and the alternative-tool tip last. The clause "; snapshots and screenshots see it" is slightly compressed and reads ambiguously, keeping it from a 5, but no sentence is wasted.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a two-required-parameter tool with full schema coverage and no output schema, the description supplies the two things the structured data can't: cross-tab scope and persistence to future tabs. Return-value behavior is out of scope and correctly omitted.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100% and both properties already document themselves as "CSS pixels". The description repeats that unit but adds no constraints such as minimums, maximums, or default behavior, so it neither compensates nor detracts. Baseline 3 applies when the schema carries the parameter burden.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
States a specific verb and resource ("Set the viewport size") and adds scope precision that the name alone lacks: it applies to every tab plus tabs opened later. It also names browser_screenshot as the route for a related need, so the agent can separate it from siblings, though it doesn't contrast with browser_scroll or browser_tabs.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Gives an explicit routing rule for one adjacent case: for a tall page, use browser_screenshot with full_page instead. That is concrete alternative guidance, but there are no exclusions or prerequisites for calling resize itself (e.g., when resizing is pointless vs scrolling).
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.