What Is an Online Highlighter?
An online highlighter is a tool that lets you select and mark text on web pages, much like using a physical highlighter on a printed page. Most online highlighters work as browser extensions for Chrome, Safari, Edge, Brave, or Opera. Once installed, they add a highlighting layer on top of any web page, so you can select a sentence or paragraph and save it with a single click.
Online highlighters have become essential for students, researchers, writers, and anyone who reads on the web regularly. Instead of bookmarking an entire page and forgetting why you saved it, you can capture the specific passages that matter to you, add your own notes, and come back to them later.
In this article, we focus on highlighters for web pages. We don't cover highlighters for PDF, video, audio, or mobile-only apps.
Two Main Approaches to Highlighting Web Pages
Before diving into how to highlight, it helps to understand the two fundamentally different approaches that highlighter tools take.
Approach 1: Highlighting on the Original Page
The first approach uses a browser extension to add a highlight layer directly on top of the original web page. When you visit any article or blog post, the extension lets you select text and highlight it in color. Your highlights stay attached to the original page, so the next time you visit, you see them again.
Popular tools in this category include Glasp, Hypothesis, Weava, and Liner.
How it works: The extension injects a small script into the page you are reading. When you select text and choose a highlight color, the extension records the position and content of that selection and stores it. Every time you return to the same URL, the extension renders your highlights on top of the original content.
Approach 2: Highlighting on a Scraped Page
The second approach works differently. Tools like Pocket, Feedly, Matter, and Instapaper scrape the content from the original page and save a copy on their own servers. You then read and highlight on their version of the article, not the original.
These tools are primarily bookmarking, read-later, or content discovery apps. Highlighting is a secondary feature, often reserved for premium plans. For example, Feedly's highlight function is only available for paid subscribers.
How it works: When you save a URL, the tool fetches and parses the page's HTML, strips ads and navigation, and stores a clean version. You highlight on this stored copy, which means your highlights are independent of the original page.
Comparing the Two Approaches
| Feature | Original Page (Extensions) | Scraped Page (Read-Later Apps) |
|---|---|---|
| Setup | Install browser extension | Create account + save each article |
| Highlight visibility | Visible on the original page | Visible only in the app |
| Content freshness | Always reads the live page | Snapshot from when you saved it |
| Sharing | Easy to share with others publicly | Usually private or limited |
| Offline access | Requires internet | Often available offline |
| Ads | Shows original page ads | Ads stripped out |
| Export options | Varies (Glasp supports .txt, .md, .csv, .html) | Usually limited |
| Cost | Often free (Glasp is free) | Highlighting often requires a paid plan |
| Risk | Highlights may break if page structure changes significantly | Content is a frozen copy, won't update |
When to choose original-page highlighting: You read a lot of web content, you want to see your highlights every time you revisit a page, and you want to share your reading with others. This is the approach we recommend for most use cases.
When to choose scraped-page highlighting: You want offline reading, distraction-free reading without ads, or you work with content that might be taken down.
How to Highlight Text with a Browser Extension
Here we walk through how to highlight text using Glasp, a free social web highlighter. Glasp is available as a browser extension for Chrome, Safari, Brave, Edge, Opera, and more. It supports four highlight colors, notes, tags, and export to Obsidian, Roam Research, Notion, Readwise, and file formats like .txt, .md, .html, and .csv.
Step 1: Sign Up and Install the Extension
First, create a free Glasp account:
Then install the browser extension for your browser:
👉 Chrome Extension (also works on Brave, Edge, and Opera)
After installing, make sure you're logged in by clicking the Glasp icon in your browser toolbar and opening the sidebar.
Glasp is available for Mac and Windows desktops.
Step 2: Select and Highlight Text
Navigate to any web page you want to read. Select the text you want to highlight. A small popup appears with four color options. Click any color, and the text is highlighted instantly. You will also see the highlighted sentence appear in the Glasp sidebar.
You can also add notes to any highlight by clicking on it and typing in the note field. This is useful for capturing your own thoughts while reading.
Step 3: Organize Highlights on Your Profile Page
All your highlights and articles are collected on your Glasp profile page. To access it, click the home icon in the sidebar or visit glasp.co.
From your profile, you can:
- Browse all highlighted articles sorted by date
- Search your highlights by keyword
- Export highlights by clicking the "Copy Content" or "Share" button
- Download in multiple formats (.txt, .md, .html, .csv)
- Sync with other tools like Readwise, Notion, Obsidian, and Roam Research
https://www.youtube.com/watch?v=7mU62hM5GP4
Step 4: Discover and Learn from Others
One of Glasp's unique features is the Explore page, where you can discover articles and highlights from other readers. You can browse by topic, search for specific subjects, and see what other learners are highlighting and noting.
Search articles on a specific topic:
https://www.youtube.com/watch?v=2hEWk7XzuaI
Search by authors:
https://www.youtube.com/watch?v=q-yAv7aJ2bY
This social layer turns highlighting from a private activity into a shared learning experience. You can access other people's perspectives on the same article, discover related content you might have missed, and build a network of learners with similar interests.
Why Highlighting Web Pages Benefits You
Highlighting is more than just coloring text. You may have heard that highlighting is a waste of time, but that claim is based on a misunderstanding of the research. A landmark 2013 study by psychologist John Dunlosky rated highlighting "low utility," and the media ran with "Stop Highlighting!" headlines. But Dunlosky's team specifically evaluated highlighting as most students practice it: dragging a marker across nearly every line with no deeper processing. The technique itself was never the problem. The execution was. (For a full breakdown of the research, see our deep dive: The Science of Highlighting.)
When used with intention, highlighting is a genuinely effective learning and productivity tool. Here's how.
Learning Benefits
Strengthens memory through active recall and spaced repetition
Humans forget most of what they read within days. The Ebbinghaus Forgetting Curve shows that without review, you lose up to 80% of new information within a week. Highlighting creates a personal review library. Tools like Glasp send weekly recap emails that surface your past highlights, creating natural spaced repetition without extra effort. Distributed practice (reviewing at intervals) is one of the two techniques Dunlosky's own research rates as "high utility."
Forces active reading and selective engagement
When you highlight, you are making a decision about what matters. Research by Yue et al. (2015) found that the act of deciding what to highlight forces readers to evaluate the importance of each sentence, creating a form of active processing that significantly improves recall. This is the opposite of passive highlighting, where you mark everything and engage with nothing.
Digital highlighting may outperform paper
A study by Mason et al. (2024) found a surprising pattern: on paper, comprehension decreased as highlighting frequency increased, but on digital texts, the reverse was true. Digital tools allow more precise selection and make it easier to search, organize, and review highlights later. This is a genuine advantage of web highlighting over traditional paper methods.
Enables social learning
Reading alone, the value you extract from an article depends entirely on your own perspective. When you can see what others have highlighted on the same article, you gain access to multiple viewpoints. Research from Cornell University shows that social annotation improves comprehension and retention by creating a form of distributed cognition. This is the principle behind Glasp's social highlighting: every reader's highlights add context that makes the article more valuable for everyone.
Contextualizes knowledge across sources
When you highlight across dozens of articles over weeks and months, patterns emerge. You start to see connections between ideas from different sources. Your highlight library becomes a personal knowledge base that reflects how your understanding evolves over time.
Productivity Benefits
Speeds up research and writing
For anyone who writes reports, articles, or academic papers, the research workflow is always the same: find sources, read, extract key points, organize, and write. Highlighting streamlines the extraction step. Instead of re-reading entire articles to find the important parts, you highlight as you go. When it's time to write, your highlights are already organized and ready to export into your writing tool.
Keeps context when sharing with others
Have you ever received a link from a colleague with just the message "Good read!"? You click it, see a 3,000-word article, and have no idea what part they found valuable or why they shared it. With highlighted links, you can share not just the article, but exactly which parts resonated with you and why. This turns vague content sharing into focused, productive communication.
Reduces re-reading
When you highlight the key points in an article, you create visual anchors. Next time you visit the page, you can scan your highlights and recall the main ideas in seconds instead of re-reading the entire piece. For researchers working with dozens of sources, this saves hours.
Best Practices for Effective Web Highlighting
Not all highlighting is equally useful. Fowler and Barker (1974) found that test performance decreased as the amount of highlighted text increased. Students who highlighted everything effectively highlighted nothing. The visual differentiation that makes highlighting useful disappears when you mark 70% of the page.
Here are research-backed practices that make your highlighting habit more effective.
Be Selective: One Sentence per Paragraph
Highlight only the key ideas, surprising facts, or passages that challenge your thinking. Research recommends highlighting no more than 10-20% of any text. For a typical paragraph, that means one sentence, possibly two. Read the full paragraph first, think about what matters, then go back and mark only the core idea. This "read first, highlight second" approach is how expert readers engage with text.
Add Your Own Notes
When paired with marginal annotations, highlighting becomes an active learning strategy comparable in effectiveness to techniques rated "high utility" by Dunlosky's research. When a sentence sparks a thought, write it down immediately. Your future self will thank you. A highlight without context can feel meaningless weeks later, but a highlight with a note like "This contradicts what I read about X" remains valuable. Glasp lets you attach notes to any highlight, keeping your thinking right next to the source material. For annotation techniques beyond highlighting, see our complete guide to annotation.
Use a Color-Coding System
Research on color and attention shows that using different colors to categorize information creates an additional layer of cognitive processing. Assigning colors to categories forces a classification step during reading, which is itself a form of elaborative processing. With Glasp's four colors, you can set up a system like this:
| Color | Meaning |
|---|---|
| Yellow | Core argument or main idea |
| Green | Supporting evidence or data |
| Blue | Questions or things to research further |
| Pink | Connections to other things you've read |
Stick with this system consistently. Over time, your brain will automatically start categorizing information as you read, and your highlights become scannable at a glance.
Review Regularly
Highlighting is only half the process. The other half is revisiting your highlights. Schedule a weekly review of your recent highlights, or use tools like Glasp's weekly recap email. During review, try to recall the context of each highlight before re-reading the source. This acts as a form of retrieval practice, which Dunlosky's research rates as one of the two highest-utility learning techniques.
Organize by Topic, Not by Source
Most people organize highlights by the article they came from. A more useful approach is to organize by topic or project. When you export highlights into tools like Notion or Obsidian, group them by theme rather than by source URL. This creates a knowledge base that supports your thinking and writing.
For a deeper look at the science behind these practices, including the full research on selectivity, color-coding, digital vs. paper highlighting, and social annotation, see our deep dive: The Science of Highlighting: Why Most People Do It Wrong (And How to Do It Right).
Frequently Asked Questions
What is the best free online highlighter for web pages?
Glasp is a free online highlighter that works as a browser extension for Chrome, Safari, Brave, Edge, and Opera. It lets you highlight text in four colors, add notes, export to multiple formats, and discover what other readers are highlighting. Unlike many other tools, Glasp's core features are completely free.
Can I highlight text on any website?
Yes, browser extension highlighters like Glasp work on almost any website. There are some exceptions: pages that block extensions (like Chrome Web Store pages or certain banking sites) and pages with unusual rendering (like some single-page applications) may not support highlighting. But for the vast majority of articles, blog posts, and web pages, highlighting works seamlessly.
Do my highlights stay on the page permanently?
With browser extension highlighters like Glasp, your highlights are displayed every time you visit the page, as long as you have the extension installed and are logged in. If the author significantly restructures the page content, some highlights may not display correctly, but the highlighted text is always saved in your Glasp profile regardless.
Can I export my highlights to other apps?
Glasp supports exporting highlights in multiple formats: .txt, .md (Markdown), .html, and .csv. It also integrates directly with Readwise, Notion, Obsidian, and Roam Research. You can export highlights from individual articles or in bulk from your profile page.
Is highlighting on web pages different from highlighting PDFs?
Yes. Web page highlighting uses browser extensions that add a layer on top of web content. PDF highlighting typically uses dedicated PDF readers or annotation tools. Some tools (including Glasp) support both, but the underlying technology is different. This guide focuses specifically on web page highlighting.
Does highlighting actually help me learn, or is it just busywork?
The famous 2013 Dunlosky study rated highlighting "low utility," but it specifically evaluated passive, indiscriminate highlighting. Later research (Yue et al., 2015; Mason et al., 2024) shows that selective highlighting combined with note-taking and review is a genuinely effective learning strategy. The key is to highlight no more than 10-20% of a text and to revisit your highlights regularly. For the full research breakdown, see The Science of Highlighting.
Can other people see my highlights?
It depends on the tool. Glasp is designed as a social highlighter, so your highlights are visible to others by default, creating a shared learning community. Other tools like Hypothesis offer both public and private modes. Scraped-page highlighters like Pocket keep highlights private. Choose the tool that matches your preference for privacy vs. social learning.
Do I need to install anything to use an online highlighter?
For original-page highlighters, yes. You need to install a browser extension. This is because the extension needs to interact with the web page you're reading to display and save highlights. If a tool claims to highlight original web pages without any extension, be cautious, as it may be redirecting you to a copy of the page on a different domain.