URL Canonicalizer

Use this skill when the same page arrives as several different URL strings - one with ?utm_source=..., one with a trailing slash, one with a #section fragment, one with the query params in a different order - and you need them all to dedupe to a single key. It lowercases the scheme/host, drops default ports and a trailing-slash-only path, removes the fragment, strips common tracking params, and sorts the rest of the query, so seen.add(canonicalize(url)) actually catches duplicates.

When to invoke

• User says: "dedup these links", "normalize scraped URLs", "stop re-posting the same article", "build a stable key from a URL".
• Items come from multiple feeds/sources and the same story has slightly different URLs.

When NOT to invoke

• You must preserve the exact original URL (it is a signed/one-time link) - keep it as-is.
• Two paths are genuinely different pages that happen to share a query - don't over-normalize.

Concrete example

User input:

These two links are the same article; make my seen-set treat them as one.

Output:

# Copy assets/canon.py into your project, then:
from canon import canonicalize, same_page

a = "https://Example.com/Post/?utm_source=tw&ref=home#top"
b = "https://example.com/Post"
canonicalize(a)      # "https://example.com/Post"
same_page(a, b)      # True

seen = set()
if (key := canonicalize(url)) not in seen:
    seen.add(key)
    process(url)

Tracking params (utm_*, fbclid, gclid, ref, ...) and the fragment are dropped, the query is sorted, and the host is lowercased, so cosmetic differences collapse to one key.

Pattern to apply

1. Split with urllib.parse.urlsplit; lowercase scheme and host (but not the path - paths can be case-sensitive).
2. Drop the default port, a trailing-slash-only path, and the fragment.
3. Remove tracking params and sort the remainder so query order is irrelevant.
4. Use the canonical string as the dedup/seen-set key, not the raw URL.

Reference: assets/canon.py.

Source

Distilled from the author's multi-source dedup pipelines. v1.0.0. See also: [[jsonl-store]], [[rss-feed-reader]], [[sqlite-state]].

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