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BIP 20 Bitcoin URI Scheme: The Proposal Before BIP 21
BIP 20 Bitcoin URI scheme explained as the closed predecessor to BIP 21, including payment links, amount encoding, compatibility and migration.
This guide explains BIP 20 Bitcoin URI scheme in plain English. It covers the problem behind the BIP, why it matters and whether the proposal is part of Bitcoin today.
TL;DR
- What it is: BIP 20 Bitcoin URI scheme proposed a clickable payment-link format before the deployed BIP 21 specification. It described how an application could launch a Bitcoin wallet with a destination, amount, label and message already populated.
- Why it matters: BIP 20 established the core idea of launchable Bitcoin payment links, but BIP 21 is the deployed standard to implement. Legacy support should be a guarded parsing and migration feature, never a reason to bypass independent address, amount and fee confirmation.
- Current position: The proposal is closed, so modern software should implement BIP 21 while treating BIP 20 as historical design evidence and a possible legacy-input case.
What this means in simple English
A BIP is a document that proposes or explains a Bitcoin idea, standard or rule. A BIP number does not mean the idea is active. Some BIPs are widely used, while others are drafts or historical proposals.
You do not need to read code to understand the main point. Start with the status, the problem being addressed and the practical effect on ordinary users, wallets, miners or node operators.
Simple example
Think of the transaction as a form passed between several authorised signers. Each person or device checks the same payment details before adding approval. Passing the form around does not make the payment safe unless every signer checks what it contains.
Key terms in plain English
- BIP:
- Bitcoin Improvement Proposal: a document describing a proposed rule, standard or process. Its status must be checked separately.
- Node:
- A computer running Bitcoin software that checks data and communicates with other peers.
The payment-link problem
Copying a Bitcoin address manually is error-prone and carries no standard way to communicate an amount, recipient label or payment note. BIP 20 proposed a bitcoin URI that browsers, QR scanners and desktop applications could hand to a registered wallet. The wallet remained responsible for showing the proposed payment and obtaining user approval before signing or broadcasting.
Scheme and destination structure
The proposal uses the bitcoin scheme followed by a destination and query parameters. URI parsing rules, percent encoding and parameter separators determine the exact values. A parser must not treat a string as trustworthy merely because it begins with bitcoin. It should validate the network address, reject malformed encoding and display the decoded destination independently.
Amounts and decimal safety
Payment amounts are represented as decimal bitcoin values rather than floating-point approximations. Implementations should parse into integer satoshis with strict precision and range checks. Locale-specific commas, exponent notation, negative values and excessive decimal places are unsafe. The wallet should show both the requested amount and the resulting fee before the user confirms.
Labels and messages
A label can help the payer recognise the recipient, while a message can describe the purpose of the request. Neither is authenticated by the URI itself. An attacker who substitutes the complete link can substitute these fields too. Wallet interfaces should escape displayed text, constrain lengths and avoid recording sensitive free-form messages in logs or analytics.
Why BIP 21 replaced it
BIP 21 refined the URI grammar, parameter handling and compatibility rules and became the deployed reference. The two proposals share the broad payment-link intent but are not interchangeable specifications. New integrations should cite BIP 21 explicitly. Legacy importers can identify BIP 20 assumptions and convert only after presenting the final decoded payment for review.
QR codes and browser handlers
A QR code is only another carrier for the same untrusted text. Camera software, browser protocol handlers and wallet registration introduce separate substitution risks. The receiving wallet should own final validation and confirmation. A website should not claim payment merely because it generated a code, and a wallet should not broadcast automatically on link activation.
How specialists test it
Developers test the proposal with made-up data on an isolated test network. They check normal cases and deliberately invalid cases. Different implementations should reach the same result before anyone relies on the proposal.
Frequently asked questions
What is BIP 20 Bitcoin URI Scheme?
BIP 20 proposed a clickable payment-link format before the deployed BIP 21 specification. It described how an application could launch a Bitcoin wallet with a destination, amount, label and message already populated.
Is BIP 20 active or supported today?
The proposal is closed, so modern software should implement BIP 21 while treating BIP 20 as historical design evidence and a possible legacy-input case.
Why does BIP 20 matter?
BIP 20 established the core idea of launchable Bitcoin payment links, but BIP 21 is the deployed standard to implement. Legacy support should be a guarded parsing and migration feature, never a reason to bypass independent address, amount and fee confirmation.
Do beginners need to use the technical details?
No. Most readers only need to understand the idea and its current status. Developers and node operators can use the primary sources when they need the exact technical rules.
Conclusion
BIP 20 established the core idea of launchable Bitcoin payment links, but BIP 21 is the deployed standard to implement. Legacy support should be a guarded parsing and migration feature, never a reason to bypass independent address, amount and fee confirmation.
Primary sources
Check the current specification status and the documentation for the exact implementation you operate before moving production funds or changing a mining node.
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