URL Encoding vs URI Encoding — What's the Real Difference?

"URL encoding" and "URI encoding" are used interchangeably by most developers, and in practice they describe the exact same mechanism: percent-encoding. But the terms aren't actually synonyms at the specification level, and understanding why clears up a lot of confusion around function names like encodeURIComponent.

URI is the broader, correct term

A URI (Uniform Resource Identifier) is any string that identifies a resource — it's defined by RFC 3986. A URL (Uniform Resource Locator) is one kind of URI: specifically one that also tells you how to locate the resource (a scheme + host + path). All URLs are URIs, but not all URIs are URLs.

https://dev-brains-ai.com/blog       ← URL (and also a URI)
mailto:someone@example.com           ← URI, not conventionally called a URL
urn:isbn:9780132350884               ← URI (URN), not a URL — no locator info
tel:+911234567890                    ← URI, not a URL

So what does "encoding" mean for each?

The encoding mechanism itself — percent-encoding — is defined once, in RFC 3986, as part of the URI spec. "URL encoding" isn't a separate algorithm; it's just the same percent-encoding applied to a URL specifically. This is exactly why JavaScript's built-in functions are named with "URI," not "URL" — they operate on the general spec:

encodeURIComponent('a value with spaces & symbols');
// → 'a%20value%20with%20spaces%20%26%20symbols'
// Named "URI" because it implements the RFC 3986 percent-encoding rules,
// applicable to any URI, not just HTTP(S) URLs

Reserved vs unreserved characters

RFC 3986 splits characters into two groups. Unreserved characters — letters, digits, - _ . ~ — never need encoding. Reserved characters have structural meaning (they separate parts of the URI) and must be encoded whenever they appear as literal data rather than as a delimiter.

• Reserved (structural) — : / ? # [ ] @ ! $ & ' ( ) * + , ; =
• Unreserved (never encoded) — A-Z a-z 0-9 - _ . ~
• Everything else (spaces, non-ASCII, most symbols) is always percent-encoded.

Why the distinction matters in practice

When you hear "URL encoding" in casual conversation, in Postman, in a form field, or in most non-spec documentation, treat it as identical to percent-encoding / URI encoding. The only place the distinction genuinely matters is when reading RFCs or writing spec-accurate documentation — pick "URI encoding" for technical precision, "URL encoding" when talking informally about web addresses specifically.

# Python's urllib module also favors "quote" and "url" terminology
from urllib.parse import quote

quote('hello world & more')
# → 'hello%20world%20%26%20more'
# Same percent-encoding, Python just calls the function "quote"

Quick terminology cheat sheet

• Percent-encoding — the formal, spec-accurate name for the %XX encoding mechanism.
• URI encoding — same mechanism, described relative to the general URI spec (RFC 3986).
• URL encoding — same mechanism, described relative to web URLs specifically; the term most developers actually use day to day.
• All three describe the identical transformation — there is no functional difference to worry about in code.

Frequently Asked Questions