Fu-Sen Add to Chrome

A Chrome extension for desktop

Turn “I don't get it”into understanding, right there.

Just select a word or passage on a web page or PDF. Read an explanation that fits the context without switching tabs, and revisit it later in the same spot.

Add to Chrome Available on the Chrome Web Store

Try it for free. Usage is limited.

Meaning in this context A Chrome extension that uses AI to quickly explain words or passages you select, right where you're reading!

How it works

Understand as you read.

Words you've never seen, words whose meaning here isn't clear, roundabout phrasing—select it and click the balloon to read an explanation right on the page. No need to open another tab to look it up.

You don't know the word at all

How it works

Sample article:People who drank coffee every day tended to have a lower risk of heart disease. However, because this was a retrospective cohort study, a causal relationship cannot be established.

  1. Select text

    Select “retrospective cohort study” in the article.

  2. A balloon appears

    A balloon appears at the end of the text you selected.

    Huh? “Retrospective”? Like, the study is just reminiscing?

  3. Click the balloon to read the explanation

    An explanation that fits the context opens right over the article.

    It's a study that looks back through past records. “Retrospective” refers to the direction in time, not to reflection or nostalgia. Because conditions are hard to control and other factors can creep in, you can say “coffee drinkers had a lower risk,” but not “coffee is the reason why.”

  4. It's saved

    The explanation is saved automatically, so you can reopen it from the balloon the next time you visit the page.

You know the words, but not what they mean here

How it works

Sample article:Even if the seller was not the true owner, a third party in good faith may be protected in some cases.

  1. Select text

    Select “third party in good faith” in the article.

  2. A balloon appears

    A balloon appears at the end of the text you selected.

    Huh? “Good faith”—so it means a well-meaning person? The law protects people for being nice?

  3. Click the balloon to read the explanation

    An explanation that fits the context opens right over the article.

    In everyday speech, “good faith” suggests good intentions, but in law it means not knowing about the relevant circumstances (knowing about them is “bad faith”). Here, it means someone who bought the item without knowing the seller had no right to sell it may be protected under certain conditions. Whether they're a nice person has nothing to do with it.

  4. It's saved

    The explanation is saved automatically, so you can reopen it from the balloon the next time you visit the page.

You don't get what the sentence means

How it works

Sample article:As I was leaving after staying far too long, my acquaintance in Kyoto asked, “Won't you have some bubuzuke before you go?” and I hurriedly got up to leave.

  1. Select text

    Select “Won't you have some bubuzuke before you go?” in the article.

  2. A balloon appears

    A balloon appears at the end of the text you selected.

    Huh? They offered rice with tea—so why rush out?

  3. Click the balloon to read the explanation

    An explanation that fits the context opens right over the article.

    On the surface it's an offer of bubuzuke (rice with tea poured over it), but in Kyoto the phrase is often described as a polite, indirect hint that it's time to go home. It's seen as a symbol of a culture where people are expected to read between the lines, and the writer picked up on that unspoken meaning and hurried to leave.

  4. It's saved

    The explanation is saved automatically, so you can reopen it from the balloon the next time you visit the page.

* All three demos are fixed examples; the articles and explanations were prepared for illustration. The legal example explains the meaning of a term and is not legal advice. Actual explanations vary depending on the words you select and the surrounding text.

Features

Deepen your understanding
without breaking your reading flow.

Read explanations on the spot

Explanations that fit the context appear right on the page you're reading. No more switching between tabs to look things up.

Ask follow-up questions

Ask about anything the explanation leaves you wondering.

Available after signing in with Google

Revisit explanations and notes

Open saved explanations from the balloon on the original page. You can also look back through your notes and history.

Note editing is available after signing in with Google

Try it for free.Usage is limited.

No sign-in required.Follow-up questions and note editing are available after signing in with Google.

To generate explanations, the selected text and necessary page information are sent to an external AI service. Saved explanations and notes are stored on your device.

Getting started

Ready to go in 3 steps.

  1. Add to Chrome

    Add the extension from the Chrome Web Store.

    Available on the Chrome Web Store

  2. Select text on a web page or PDF

    Use your mouse to select a word or passage you're curious about.

  3. Click the balloon

    Click the balloon that appears at the end of your selection to open an explanation.

The first time, you can choose to sign in with Google or try it without signing in.

Why we built it

Bringing “reading” and “understanding”
together.

For work and study, I often find myself reading web articles and PDFs in fields I'm not familiar with, looking things up as I go.

Every time I hit a word or sentence I didn't understand, I'd open an AI chat in another tab, explain the original text and its context, and ask my question. After reading the answer, I'd go back, find where I'd left off, and keep reading. I repeated this over and over.

Each step is a small hassle, but every time, it interrupts your reading and your train of thought. And whatever you figured out never stays on the original page, so days later I'd find myself looking up the same thing again, thinking, “Didn't I already look this up?”

So what if you could just select what you don't understand, read the explanation right there, and keep on reading? What if what you learned stayed in that spot, so you could recall it the next time you read the page? That idea is how I started building Fu-Sen.

Before

  1. Read
  2. Get stuck
  3. Open another tab
  4. Write a question
  5. Read the explanation
  6. Go back and reread

With Fu-Sen

  1. Read
  2. Get stuck
  3. Understand on the spot
  4. Keep reading

When rereading later

  1. Open the same page
  2. The balloon is still there
  3. Recall what you understood before

As I kept using it myself, I found it much easier to keep my research moving and to read on while understanding things one at a time. I decided to release it in the hope that it would help others who also want to read carefully, working through what they don't understand one step at a time.

I'll keep using Fu-Sen myself as one of its users, and keep making it a little better over time.

Share your thoughts and feedbackhello@fu-sen.app

FAQ

Frequently asked questions

Is it free?

Yes, you can use it for free. Usage is limited. You can check your usage and the next reset date and time in the extension's settings.

Do I need to sign in?

You can try the basic explanations without signing in. Signing in with Google also unlocks follow-up questions and note editing.

Does it work with PDFs?

It works with PDFs where you can select the text. PDFs made only of images are not supported. To use it with PDF files on your computer, allow file access in Chrome's extension settings.

Is this extension safe?

Rest assured. Fu-Sen passed review by Google's official Chrome Web Store before being published.

Before publication, the Chrome Web Store reviews whether an extension complies with Google's Developer Program Policies. The review uses automated checks, with additional manual checks when needed. Google's published review process and Developer Program Policies describe review criteria and publication requirements such as the following.

  • The permissions requested are necessary for the extension's features and are used appropriately
  • How user data is collected, used, and sent externally is properly disclosed
  • The extension's actual behavior matches its Privacy Policy and its disclosures on the Chrome Web Store
  • User data and credentials are handled securely
  • The extension's purpose and behavior are clear, and it includes no features that deceive users
  • The extension's behavior can be verified from its code, with no prohibited obfuscation or improper execution of external code
  • As an extension offered on the Chrome Web Store, it actually works and provides meaningful value

Because Fu-Sen explains text you select on a web page right where you are, it uses permissions that let it run on a wide range of websites. Google itself identifies broad site access permissions such as <all_urls> as something it reviews with particular care, checking whether the requested permissions are truly necessary and used appropriately.

Rather than relying only on passing the Chrome Web Store review, Fu-Sen is designed with privacy and safety in mind as much as possible: it requests no more permissions than necessary, stores explanations and notes on your device by default, and clearly states in its Privacy Policy what information is sent to external services.

Where are my explanations and notes stored?

They're stored on your device, in your Chrome profile. They are not automatically synced to other devices. If a page's content or structure changes, they may not appear in their original spot, but you can still find your saved explanations in your history.

What information is sent to the AI?

When you request an explanation, the selected text, the surrounding context needed for the explanation, page information such as the page title and URL, and the content of your question are sent to an external AI service. For details, see our Privacy Policy.

Where can I use it?

You can use it with Chrome on a computer. Extensions aren't available on smartphones, but you can still view this page.

Give it a try in your everyday
research and studying.

The next time you run into something you don't understand, just select it and click the balloon.

Add to Chrome Available on the Chrome Web Store