tldextract Documentation

Technical Documentation: john-kurkowski/tldextract

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Overview (`README.md`) Copy Section

tldextract [](https://badge.fury.io/py/tldextract) [](https://github.com/john-kurkowski/tldextract/actions/workflows/ci.yml)

tldextract accurately separates a URL's subdomain, domain, and public suffix,
using the Public Suffix List (PSL).

Why? Naive URL parsing like splitting on dots fails for domains like
forums.bbc.co.uk (gives "co" instead of "bbc"). tldextract handles the edge
cases, so you don't have to.

Quick Start Copy Chapter

>>> import tldextract

>>> tldextract.extract('http://forums.news.cnn.com/')
ExtractResult(subdomain='forums.news', domain='cnn', suffix='com', is_private=False)

>>> tldextract.extract('http://forums.bbc.co.uk/')
ExtractResult(subdomain='forums', domain='bbc', suffix='co.uk', is_private=False)

>>> # Access the parts you need
>>> ext = tldextract.extract('http://forums.bbc.co.uk')
>>> ext.domain
'bbc'
>>> ext.top_domain_under_public_suffix
'bbc.co.uk'
>>> ext.fqdn
'forums.bbc.co.uk'

Install Copy Chapter

pip install tldextract

How-to Guides Copy Chapter

How to disable HTTP suffix list fetching for production Copy Section

no_fetch_extract = tldextract.TLDExtract(suffix_list_urls=())
no_fetch_extract("http://www.google.com")

Or set the default for new extractors with an empty environment variable. Set
it before importing tldextract to affect the module-level extract function:

export TLDEXTRACT_PUBLIC_SUFFIX_LIST_URLS=""

With fetching disabled, tldextract uses its bundled snapshot if no matching
cache entry exists. See Caching behavior for details.

How to set a custom cache location Copy Section

Via environment variable:

export TLDEXTRACT_CACHE="/path/to/cache"

Or in code:

custom_cache_extract = tldextract.TLDExtract(cache_dir="/path/to/cache/")

How to update TLD definitions Copy Section

Command line:

tldextract --update

Or delete the cache folder:

rm -rf $HOME/.cache/python-tldextract

How to treat private domains as suffixes Copy Section

extract = tldextract.TLDExtract(include_psl_private_domains=True)
extract("waiterrant.blogspot.com")
# ExtractResult(subdomain='', domain='waiterrant', suffix='blogspot.com', is_private=True)

How to use a custom suffix list Copy Section

Local suffix list

extract = tldextract.TLDExtract(
    suffix_list_urls=["file:///path/to/your/list.dat"],
    cache_dir="/path/to/cache/",
    fallback_to_snapshot=False,
)

Remote suffix list

extract = tldextract.TLDExtract(
    suffix_list_urls=["https://myserver.com/suffix-list.dat"]
)

Set the default suffix list sources

For either local or remote lists, set the default through a newline-delimited
environment variable:

export TLDEXTRACT_PUBLIC_SUFFIX_LIST_URLS="https://myserver.com/suffix-list.dat"

New TLDExtract() instances read this value when constructed. An explicit
suffix_list_urls argument takes precedence. Set the environment variable
before importing tldextract to affect the module-level extract function.

An existing local path in TLDEXTRACT_PUBLIC_SUFFIX_LIST_URLS is converted to
a file:// URL, like the --suffix_list_url command line option.

How to set the suffix list fetch timeout Copy Section

Set a default timeout in seconds before starting Python:

export TLDEXTRACT_DEFAULT_FETCH_TIMEOUT="1.2"

Or set it for one extractor in code:

extract = tldextract.TLDExtract(cache_fetch_timeout=1.2)

A single value applies separately to the connection and response-read phases of
each remote Public Suffix List request.

How to add extra suffixes Copy Section

extract = tldextract.TLDExtract(extra_suffixes=["foo", "bar.baz"])

How to validate URLs before extraction Copy Section

from urllib.parse import urlsplit

extract = tldextract.TLDExtract()
split_url = urlsplit("https://example.com/path")
result = extract.extract_urllib(split_url)

Command Line Copy Chapter

$ tldextract http://forums.bbc.co.uk
forums bbc co.uk

$ tldextract --update  # Update cached suffix list
$ tldextract --help    # See all options

Understanding Domain Parsing Copy Chapter

Public Suffix List Copy Section

tldextract uses the Public Suffix List, a
community-maintained list of domain suffixes. The PSL contains both:

• Public suffixes: Where anyone can register a domain (.com, .co.uk,
  .org.kg)
• Private suffixes: Operated by companies for customer subdomains
  (blogspot.com, github.io)

Web browsers use this same list for security decisions like cookie scoping.

Suffix vs. TLD Copy Section

While .com is a top-level domain (TLD), many suffixes like .co.uk are
technically second-level. The PSL uses "public suffix" to cover both.

Default behavior with private domains Copy Section

By default, tldextract treats private suffixes as regular domains:

>>> tldextract.extract('waiterrant.blogspot.com')
ExtractResult(subdomain='waiterrant', domain='blogspot', suffix='com', is_private=False)

To treat them as suffixes instead, see
How to treat private domains as suffixes.

Default behavior with unlisted suffixes Copy Section

Unlike the formal PSL algorithm,
tldextract does not apply the implicit * rule when no suffix matches. For an
unlisted final label, suffix remains empty so callers can distinguish configured
public suffixes from unknown, invalid, or internal hostnames.

Hostname representation Copy Section

tldextract identifies public suffix boundaries but does not validate or
canonicalize hostnames. Returned strings can retain the input's casing and its
Unicode or ASCII-compatible encoding (ACE, commonly called Punycode).
Equivalent IDNA hostnames can therefore produce textually different values even
when tldextract identifies the same suffix boundary.

Before using suffix, fqdn, or joined-domain properties in equality checks,
allowlists, blocklists, or other security decisions, validate and normalize
both hostnames to the same IDNA representation. IDNA defines label equivalence
in terms of A-labels. See
RFC 5890, section 2.3.2.4.

Caching behavior Copy Section

By default, tldextract fetches the latest Public Suffix List on first use and
caches it indefinitely in $HOME/.cache/python-tldextract.

The cache key includes the configured URLs. An empty URL list does not reuse a
cache entry fetched with the standard URLs; if no entry exists for the empty
URL list, tldextract uses its bundled snapshot.

URL validation Copy Section

tldextract accepts any string and is very lenient. It prioritizes ease of use
over strict validation, extracting domains from any string, even partial URLs or
non-URLs.

FAQ Copy Chapter

Can you add/remove suffix \_\_\_\_? Copy Section

tldextract doesn't maintain the suffix list. Submit changes to
the Public Suffix List.

Meanwhile, add extra suffixes with the
extra_suffixes parameter, or fork the PSL and
use a custom suffix list with the
suffix_list_urls parameter.

My suffix is in the PSL but not extracted correctly Copy Section

Check if it's in the "PRIVATE" section. See
How to treat private domains as suffixes.

Why does it parse invalid URLs? Copy Section

See URL validation and
How to validate URLs before extraction.

Contribute Copy Chapter

Setting up Copy Section

1. Install uv.
2. git clone this repository.
3. Change into the new directory.
4. uv sync

Running tests Copy Section

uv run pytest          # Fast local suite
uv run tox -e py310    # Supported-version suite
uv run tox --parallel  # Full matrix
uv run ruff format .   # Format code

History Copy Chapter

This package started from a
StackOverflow answer
about regex-based domain extraction. The regex approach fails for many domains,
so this library switched to the Public Suffix List for accuracy.

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