Wayback Machine — Internet Archive CDX

1. Summary

The Internet Archive's Wayback Machine has captured ~900B+ web pages since 1996. The CDX server API indexes those captures by URL, timestamp, and content hash. Free, anonymous, no auth.

2. Access Methods

CDX server: https://web.archive.org/cdx/search/cdx
Wayback URL: https://web.archive.org/web/<timestamp>/<url>
Save Page Now (write): https://web.archive.org/save/<url> (different API)
Auth: None
Rate limit: Generous; be polite (~1 req/s)

3. Data Schema

Key fields emitted by fetch_wayback.py:

Column	Type	Description
`url`	str	Original URL captured
`timestamp`	str	YYYYMMDDHHMMSS (CDX format)
`wayback_url`	str	Direct replay URL
`mimetype`	str	Content-type at capture
`status`	str	HTTP status (typically 200)
`digest`	str	SHA1 of capture content (collapse-friendly)
`length`	str	Byte length of capture

4. Coverage

1996 → present
~900B+ captures across ~700M domains
Updated continuously by automated crawls + manual saves
Some domains have aggressive coverage (news), others sparse (private)

5. Cross-Reference Potential

Wikipedia ↔ Reverse-lookup pages cited as references that have since disappeared
News URLs ↔ Original article content when present-day URLs 404
Corporate websites ↔ Historical "About" pages, executive bios that have been scrubbed

The Wayback CDX is most useful as a content-recovery layer when other sources point to URLs that no longer exist.

6. Data Quality

robots.txt-blocked domains may have spotty or no coverage
Captures vary in completeness (HTML may be saved without CSS/JS)
Some content is excluded by domain owner request (DMCA, etc.)
Coverage of "deep links" (URLs with query strings) is uneven
Time resolution is per-capture, not continuous — gaps are common

7. Acquisition Script

Path: scripts/fetch_wayback.py

# All captures of a specific URL
python3 SKILL_DIR/scripts/fetch_wayback.py --url "https://example.com/page" \
    --out data/wb.csv

# All captures of a host
python3 SKILL_DIR/scripts/fetch_wayback.py --url "example.com" \
    --match host --out data/wb.csv

# All captures of a domain + subdomains
python3 SKILL_DIR/scripts/fetch_wayback.py --url "example.com" \
    --match domain --out data/wb.csv

# Only unique-content captures within a date window
python3 SKILL_DIR/scripts/fetch_wayback.py --url "example.com" \
    --match host --collapse digest \
    --from-date 2020-01-01 --to-date 2023-12-31 \
    --out data/wb.csv

8. Legal & Licensing

Internet Archive captures are made under fair-use research provisions
Replay URLs are stable references — citing them is encouraged
Internet Archive non-profit terms of use govern content
Some content is rights-restricted; replay may be blocked even if the CDX entry shows it as captured

9. References

CDX server docs: https://github.com/internetarchive/wayback/blob/master/wayback-cdx-server/README.md
Wayback API: https://archive.org/help/wayback_api.php
Internet Archive: https://archive.org/