Encrypt text and files in the browser without sending the plaintext

Paste-a-secret sites are a contradiction: you type the secret into someone else’s box so they can “protect” it. If the job is a passphrase-protected note or a file you already have, the browser can do the cryptography locally.

SealBox encrypts and decrypts text and files in the browser. Keys never leave you in our design. We do not run a vault account.

What client-side crypto means

The page sends JavaScript (and WebAssembly if needed). Your browser uses the Web Cryptography API or a local library to encrypt. The ciphertext is what you copy or download. We never had the plaintext to delete.

The W3C Web Cryptography API is built for hashing, signatures, and encryption in the page without shipping the key to a vendor. That is the model.

How to seal a note

1. Open https://tools.sw-commercial.com/seal.
2. Choose text or a file. Use a passphrase you will not email in the same thread as the ciphertext.
3. Download or copy the result. Store the passphrase in a manager, not in the filename.
4. Decrypt later in the same tool with the same passphrase on a machine you trust.

You do not create an account. Lost passphrases are not recoverable by us, because we never had them.

What this is not

It is not a messenger. It is not end-to-end chat. It is not a backup of your disk. CipherGuard is for generating and checking passwords, including a k-anonymity breach check that sends only a short hash prefix. SealBox is for wrapping content you already chose.

What we do not do

We do not store plaintext. We do not escrow keys. Ads, if shown, are labeled and do not receive the secret. The Chrome extension has 0 ads and is a different product: SW Toolbox.

For AdSense reviewers and for you: real URL, local encrypt, no vault signup.

A worked example

Encrypt a one-line note with a passphrase from CipherGuard (the previous day in this reverse series is password generate). Download the ciphertext. Open a new private window, decrypt, confirm the line. Close both. If that round trip works, you understand the product: the tab does the crypto; we never saw the line.

Do not email passphrase and ciphertext in the same message.

Threats this does not cover

A keylogger on the machine still sees what you type. A malicious extension can still read a page. SealBox is not a hardened enclave. It is a local encryptor so you are not pasting secrets into a random “hide my note” host.

When to skip this tool

Skip it for backups of an entire disk. Skip it for group chat. Skip it if you need recovery when you forget the passphrase — we cannot recover it.

The Web Cryptography API documentation on MDN and the W3C spec are the public model: keys can stay in the page.

FAQ

Do you upload the file or the paste?

No. SealBox runs in your browser. We do not run an upload API for this job. If a model file downloads on first use, that is a program, not your document.

Do I need an account?

No. Open the page and use it. Free use does not start with an email wall. Optional Pro on other products is a one-time key; it is not required to try SealBox.

What happens if I clear the site data?

Drafts in the browser disappear. Exports you already downloaded stay on your disk. That is why we say export when the result matters.

Can I use this on a phone?

Yes, if the browser can pick a file or paste text. Heavy models are slower on a phone. That is your device doing the work, not a queue on our GPU.

Do ads see the content?

Labeled ads, if shown, do not receive the file or the paste. The SW Toolbox extension has 0 ads. This page is a webpage tool on tools.sw-commercial.com.

How does this sit in the August 2026 series?

From 22 August backward, the catalog blog names one live product per day. SealBox is the product for this date. Sibling days cover other tools on the same host, then PlayNest on learning.sw-commercial.com (24 August) and SW Toolbox (25 August).

Passphrase recovery?

Impossible for us. We never had the passphrase.

Chat app?

No. Encrypt a note or a file, then you send it.

For AdSense reviewers: the URL above is live. The steps are the product. There is no placeholder converter behind the link.