Quote from coinguides on May 1, 2019, 4:39 am

URI means Unique Resource Identifier. It is a protocol within your web browser that is used to identify resource on your computer. Usually it will be in link format (URL) which upon triggering it performs specified action. Have you not come across mailto: handler : mailto:someone@gmail.com. Websites usually displays it in a hyperlink format like this:

<a href="mailto:someone@gmail.com">Email Address</a>

Result: Email Address.

Upon clicking the hyperlink; a popup window will open asking you to choose the email program. Open the email program and it will display the email address embedded in the link.

Likewise, Bitcoin URI is a payment URI or payment request link. Websites and other payment service that accepts Bitcoin uses Bitcoin URI scheme for making Bitcoin payments.

bitcoin:3JK2dFmWA58A3kukgw1yybotStGAFaV6Sg

Both Bitcoin URI and QR codes are used to share payment requests. It allows users to send and receive Bitcoin easily just by clicking the link or scanning the QR code.

If you are running an E-commerce website, application or looking to add "Donate me in Bitcoin" button then you can use this Bitcoin URI as a payment request link. The request URI contains wallet address, amount, label and message if any.

With this link users can easily send payments to your Bitcoin address. They don't have to manually copy paste your Bitcoin address in their wallet anymore.

Upon clicking the Bitcoin URI link you'll get a popup. You can either open Bitcoin core or electrum wallet depending on what wallet software you've installed on your computer.

Choose the wallet software and it will automatically open the send tab along with the Bitcoin address and amount (if present) depending on the information contained in the URI scheme. It simply copies all the transaction information directly into your wallet client so that you can make payment easily.

Bitcoin URI scheme supports Bitcoin core wallet, Electrum wallet, MultiBit, Armory and many others. Also it works with both Android and IOS Bitcoin wallets.

The simple syntax is:

bitcoin:<address>[?amount=<amount>][?label=<label>][?message=<message>]

Here are some common examples of Bitcoin URI:

Just the address

bitcoin:3JK2dFmWA58A3kukgw1yybotStGAFaV6Sg

Address with name

bitcoin:3JK2dFmWA58A3kukgw1yybotStGAFaV6Sg?label=Coin-Guides

Requesting 1 BTC

bitcoin:3JK2dFmWA58A3kukgw1yybotStGAFaV6Sg?amount=1.00000000&label=Coin-Guides

Requesting 1 BTC with message

bitcoin:3JK2dFmWA58A3kukgw1yybotStGAFaV6Sg?amount=1.00000000&label=Coin-Guides&message=Donation%20for%20Coin%20Guides

For more detailed information on Bitcoin URI see the official BIP21 spec.