Main threadWhat it means for you.

The single browser thread that runs scripts, styles and layout and handles user input.

Growth Score · Activation

Definition

What it means

Because one thread does most of the work, heavy JavaScript makes pages feel frozen. Keeping tasks short and deferring non-essential code keeps it free. Web workers can take on some calculations.

In Growth Score

Part of your score

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Guides that cover it

Checkout audit: 12 leaksTwelve places a sale leaks, in cost order, with a test and a fix for each one.When to redesign your siteHow to tell a real redesign need from vanity, and how to do it without losing rankings.Fast for real visitorsRead real visits, then fix images, scripts, layout shifts and the slow start.

Activation

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FAQ

Quick answers

What is Main thread?

The single browser thread that runs scripts, styles and layout and handles user input.

Where does it sit in Growth Score?

It belongs to the Activation pillar, one of the 12 pillars your score is built from.

What should I read next?

Start with Long task and Interaction to Next Paint, then browse the other terms in Activation.

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How does your site score?

Growth Score reads your site and scores its Activation pillar against sites like yours.

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Your Growth Score is 100

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