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URL

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In brief · quick answer

A URL (Uniform Resource Locator) is a text string that specifies the exact location of a resource on the internet and how to access it.

§ 1 Definition

A URL is the address of a web resource. It is what you type into a browser's address bar. URLs have a structured format: `scheme://host:port/path?query#fragment`. The scheme (protocol) tells the browser how to communicate: `http://`, `https://`, `ftp://`, `mailto:`. The host identifies the server, usually via a domain name that the DNS system resolves to an IP address. The path identifies the specific resource on the server. Query strings pass parameters, and fragments target specific sections within a page. URLs are part of the larger URI (Uniform Resource Identifier) family. Every URL is a URI, but not every URI is a URL. Understanding URL structure is essential for everything from SEO (clean URLs rank better) to security (checking URLs prevents phishing).

§ 2 URL structure

Breakdown of a URL: `https://www.example.com:443/products?id=42#reviews`. `https` is the scheme. `www.example.com` is the domain. `443` is the port (default for HTTPS). `/products` is the path. `id=42` is the query string. `#reviews` is the fragment (never sent to the server, handled client-side).

§ 3 Encoding and normalization

URLs can only contain ASCII characters. Non-ASCII characters must be percent-encoded (spaces become `%20`, Unicode characters get multi-byte encoding). Browsers normalize URLs by lowercasing the scheme and host, decoding unnecessary percent-encoding, and removing default ports. This normalization is critical for SEO: `Example.com/Page` and `example.com/page` may both work, but search engines treat them as duplicates.

§ 4 Common misconception

The fragment (hash) is never sent to the server. If you are building a single-page application with hash-based routing, the server only sees the path before the hash. This matters for server configuration and SEO. Use the History API for clean URLs instead.

§ 5 Note

URLs are case-sensitive for the path but case-insensitive for the scheme and host. This subtlety causes many broken links and duplicate content issues.

§ 6 In code

```javascript
// Parsing a URL in JavaScript
const url = new URL('https://example.com/path?q=search#section');
console.log(url.hostname); // 'example.com'
console.log(url.pathname); // '/path'
console.log(url.searchParams.get('q')); // 'search'
```

§ 7 Common questions

Q. What is the difference between a URL and a URI?: A. A URI identifies a resource. A URL is a type of URI that also provides the means to locate it. All URLs are URIs.
Q. How long can a URL be?: A. There is no official limit, but most browsers support up to 64K characters. Internet Explorer capped at 2,083 characters. Keep URLs short for practical reasons.

Key takeaways

URLs specify both the location of and the access method for web resources.
URL structure affects SEO, security, and user experience.
Always use clean, descriptive URLs without unnecessary parameters.

How Atomic Glue helps

Atomic Glue builds clean URL structures that search engines love and users trust. Our SEO & GEO services include URL strategy and canonicalization.

Get in touch

# URL

A URL (Uniform Resource Locator) is a text string that specifies the exact location of a resource on the internet and how to access it.

Category: Web Development (also: Infrastructure, General)

Author: Atomic Glue Team

## Definition

A URL is the address of a web resource. It is what you type into a browser's address bar. URLs have a structured format: `scheme://host:port/path?query#fragment`. The scheme (protocol) tells the browser how to communicate: `http://`, `https://`, `ftp://`, `mailto:`. The host identifies the server, usually via a [domain name](/glossary/dns) that the [DNS](/glossary/dns) system resolves to an [IP address](/glossary/ip-address). The path identifies the specific resource on the server. Query strings pass parameters, and fragments target specific sections within a page. URLs are part of the larger URI (Uniform Resource Identifier) family. Every URL is a URI, but not every URI is a URL. Understanding URL structure is essential for everything from SEO (clean URLs rank better) to security (checking URLs prevents phishing).

## URL structure

## Encoding and normalization

## Common misconception

## Note

URLs are case-sensitive for the path but case-insensitive for the scheme and host. This subtlety causes many broken links and duplicate content issues.

## In code

## Common questions
Q: What is the difference between a URL and a URI?
A: A URI identifies a resource. A URL is a type of URI that also provides the means to locate it. All URLs are URIs.
Q: How long can a URL be?
A: There is no official limit, but most browsers support up to 64K characters. Internet Explorer capped at 2,083 characters. Keep URLs short for practical reasons.

## Key takeaways

URLs specify both the location of and the access method for web resources.
URL structure affects SEO, security, and user experience.
Always use clean, descriptive URLs without unnecessary parameters.

## Related entries

Last updated June 2026. Permalink: atomicglue.co/glossary/url