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"Same-site" and "same-origin" are frequently cited but often misunderstood
terms. For example, they're used in the context of page transitions,
`fetch()` requests, cookies, opening popups, embedded resources, and
iframes. This page explains what they are and how they're different from each
other.
## Origin
 The structure of an origin.
"Origin" is a combination of a
[scheme](https://developer.mozilla.org/docs/Web/HTTP/Basics_of_HTTP/Identifying_resources_on_the_Web#Scheme_or_protocol)
(also known as the
[protocol](https://developer.mozilla.org/docs/Glossary/Protocol), for
example [HTTP](https://developer.mozilla.org/docs/Glossary/HTTP) or
[HTTPS](https://developer.mozilla.org/docs/Glossary/HTTPS)), a
[hostname](https://en.wikipedia.org/wiki/Hostname), and a
[port](https://developer.mozilla.org/docs/Web/HTTP/Basics_of_HTTP/Identifying_resources_on_the_Web#Port)
(if specified). For example, given a URL of `https://www.example.com:443/foo` ,
the "origin" is `https://www.example.com:443`.
### "Same-origin" and "cross-origin"
Websites that have the same combination of scheme, hostname, and port are
considered "same-origin". Everything else is considered "cross-origin".
| Origin A | Origin B | "Same-origin" or "cross-origin"? |
|---|---|---|
| https://www.example.com:443 | https://**www.evil.com**:443 | Cross-origin: different domains |
| https://www.example.com:443 | https://**example.com**:443 | Cross-origin: different subdomains |
| https://www.example.com:443 | https://**login**.example.com:443 | Cross-origin: different subdomains |
| https://www.example.com:443 | **http**://www.example.com:443 | Cross-origin: different schemes |
| https://www.example.com:443 | https://www.example.com:**80** | Cross-origin: different ports |
| https://www.example.com:443 | **https://www.example.com:443** | **Same-origin: exact match** |
| https://www.example.com:443 | **https://www.example.com** | **Same-origin: implicit port number (443) matches** |
## Site
> [!IMPORTANT]
> **Key Point:** The [specification for "site"](https://github.com/whatwg/url/issues/448) includes the scheme. This has been true since late 2019. Before "site" included schemes, ["schemeful same-site"](https://web.dev/articles/schemeful-samesite) was commonly used. Now, "schemeful same-site" is referred to as "same-site," and the old form of same-site is called "schemeless same-site." For more information, see ["Schemeless same-site"](https://web.dev/articles/same-site-same-origin#schemeless-same-site).
 The parts of a URL that make up a site.
[Top-level domains (TLDs)](https://developer.mozilla.org/docs/Glossary/TLD) such
as `.com` and `.org` are listed in the
[Root Zone Database](https://www.iana.org/domains/root/db). In the previous
example, "site" is a combination of the
[scheme](https://developer.mozilla.org/docs/Web/HTTP/Basics_of_HTTP/Identifying_resources_on_the_Web#Scheme_or_protocol),
the [TLD](https://developer.mozilla.org/docs/Glossary/TLD), and the part of the
domain just before it (We call it TLD+1). For example, given a URL of
`https://www.example.com:443/foo`, the "site" is `https://example.com`.
### Public Suffix List and eTLD
For domains with elements such as `.co.jp` or `.github.io`, just using `.jp` or
`.io` isn't specific enough to identify the "site". There's no way to
algorithmically determine the level of registrable domains for a particular TLD.
To help with that, the [Public Suffix List](https://wiki.mozilla.org/Public_Suffix_List)
defines a list of public suffixes, also called *effective TLDs (eTLDs)* . The
list of eTLDs is maintained at [publicsuffix.org/list](https://publicsuffix.org/list/).
To identify the "site" part of a domain that includes an eTLD, apply the same
practice as the example with `.com`. Taking
`https://www.project.github.io:443/foo` as an example, the scheme is `https`,
the eTLD is `.github.io` and the eTLD+1 is `project.github.io`, so
`https://project.github.io` is considered the "site" for this URL.
 The parts of a URL with an eTLD.
### "same-site" and "cross-site"
Websites that have the same scheme and the same eTLD+1 are considered
"same-site". Websites that have a different scheme or a different eTLD+1 are
"cross-site".
| Origin A | Origin B | "Same-site" or "cross-site"? |
|---|---|---|
| https://www.example.com:443 | https://**www.evil.com**:443 | Cross-site: different domains |
| https://www.example.com:443 | https://**login**.example.com:443 | **Same-site: different subdomains don't matter** |
| https://www.example.com:443 | **http**://www.example.com:443 | Cross-site: different schemes |
| https://www.example.com:443 | https://www.example.com:**80** | **Same-site: different ports don't matter** |
| https://www.example.com:443 | **https://www.example.com:443** | **Same-site: exact match** |
| https://www.example.com:443 | **https://www.example.com** | **Same-site: ports don't matter** |
### "Schemeless same-site"
The definition of "same-site" changed to include the URL scheme as part of the
site to prevent HTTP being used as a
[weak channel](https://tools.ietf.org/html/draft-west-cookie-incrementalism-01#page-8).
The older concept of "same-site" without scheme comparison is now called
"schemeless same-site". For example, `http://www.example.com` and
`https://www.example.com` are considered schemeless same-site but not same-site,
because only the eTLD+1 part matters and the scheme isn't considered.
| Origin A | Origin B | "Schemeless same-site" or "cross-site"? |
|---|---|---|
| https://www.example.com:443 | https://**www.evil.com**:443 | Cross-site: different domains |
| https://www.example.com:443 | https://**login**.example.com:443 | **Schemeless same-site: different subdomains don't matter** |
| https://www.example.com:443 | **http**://www.example.com:443 | **Schemeless same-site: different schemes don't matter** |
| https://www.example.com:443 | https://www.example.com:**80** | **Schemeless same-site: different ports don't matter** |
| https://www.example.com:443 | **https://www.example.com:443** | **Schemeless same-site: exact match** |
| https://www.example.com:443 | **https://www.example.com** | **Schemeless same-site: ports don't matter** |
## How to check if a request is "same-site", "same-origin", or "cross-site"
Browser Support
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stop-color='%23fff44f' stop-opacity='.2'/%3E%3Cstop offset='.6' stop-color='%23fff44f' stop-opacity='0'/%3E%3C/linearGradient%3E%3C/defs%3E%3Cpath d='M479 166c-11-25-32-52-49-60a249 249 0 0 1 25 73c-27-68-73-95-111-155a255 255 0 0 1-8-14 44 44 0 0 1-4-9 1 1 0 0 0 0-1 1 1 0 0 0-1 0c-60 35-81 101-83 134a120 120 0 0 0-66 25 71 71 0 0 0-6-5 111 111 0 0 1-1-58c-25 11-44 29-58 44-9-12-9-52-8-60l-8 4a175 175 0 0 0-24 21 210 210 0 0 0-22 26 203 203 0 0 0-32 73l-1 2-2 15a229 229 0 0 0-4 34v1a240 240 0 0 0 477 40l1-9c5-41 0-84-15-121zM202 355l3 1-3-1zm55-145zm198-31z' fill='url(%23ff-a)'/%3E%3Cpath d='M479 166c-11-25-32-52-49-60 14 26 22 53 25 72v1a207 207 0 0 1-206 279c-113-3-212-87-231-197-3-17 0-26 2-40-2 11-3 14-4 34v1a240 240 0 0 0 477 40l1-9c5-41 0-84-15-121z' fill='url(%23ff-b)'/%3E%3Cpath d='M479 166c-11-25-32-52-49-60 14 26 22 53 25 72v1a207 207 0 0 1-206 279c-113-3-212-87-231-197-3-17 0-26 2-40-2 11-3 14-4 34v1a240 240 0 0 0 477 40l1-9c5-41 0-84-15-121z' fill='url(%23ff-c)'/%3E%3Cpath 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[Source](https://developer.mozilla.org/docs/Web/HTTP/Reference/Headers/Sec-Fetch-Site)
All modern browsers send requests with a
[`Sec-Fetch-Site` HTTP header](https://developer.mozilla.org/docs/Web/HTTP/Headers/Sec-Fetch-Site).
The header has one of the following values:
- `cross-site`
- `same-site` (refers to schemeful same-site)
- `same-origin`
- `none`
You can examine the value of `Sec-Fetch-Site` to determine whether the request
is same-site, same-origin, or cross-site.
You can reasonably trust the value of the `Sec-Fetch-Site` header, because:
- [HTTP headers starting with `Sec-` can't be modified by JavaScript](https://www.w3.org/TR/fetch-metadata/#sec-prefix)
- The browser always sets these headings.
> [!IMPORTANT]
> **Key Point:** Even if a random HTTP client sends the server a manipulated value for the `Sec-Fetch-Site` header, no user or browser is harmed by breaking the same-origin policy.