- Python 100%
Sergei Poljanski
43a88182cd
The rDNS check had one failure bucket, so "PTR points at a different network" and "no PTR exists" landed in the same column. Those mean opposite things. Meta's IPv6 crawler space publishes no PTR records at all, so every genuine Meta request was reported under a heading that read as forgery - an accusation the data did not support. Split the outcome three ways: FORGED (a PTR exists and points elsewhere - the only column that is evidence of a lie), no-PTR (nothing to check, unknown), and PTR ok. Add an ASN fallback for the no-PTR case, restricted to vendors whose ASN is single-tenant. Meta is the motivating case: it publishes no range file - their documentation says to email webmasters@meta.com - and no PTR records, so without this there is nothing to check at all. AS32934 is Meta's own network and cannot be rented, which is what makes the match meaningful. This is deliberately not applied to cloud ASNs: genuine YouBot and genuine Amazonbot both live in AS14618 alongside every EC2 instance a spoofer could rent, so a match there would prove only that the traffic came from a cloud. Verified against real traffic: Meta now shows 1 ASN-confirmed request against 14 forged ones from googleusercontent.com hosts, which is the distinction the old single column destroyed. Assisted-by: Claude:opus-5 |
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|---|---|---|
| crawler-alert.env.example | ||
| crawler-alert.py | ||
| crawler-alert.service | ||
| crawler-alert.timer | ||
| crawler-weekly.service | ||
| crawler-weekly.timer | ||
| LICENSE | ||
| README.md | ||
| traefik-accesslog.yml | ||
crawler-alert
Tells you which AI crawlers are really visiting your site, and which are lying about it.
Reads a Traefik access log, mails a threshold alert daily and a summary
weekly. Every bot is checked against its vendor's published IP ranges,
so a forged User-Agent does not get counted as the real thing.
Python 3.9+, standard library only. No database, no daemon, no agent.
Why user-agent alone is not enough
A User-Agent header is a string the client chooses. Anyone can send
ClaudeBot/1.0. On the Forgejo instance this was written for, measured
over 2.27M requests between November 2025 and August 2026:
| Bot | Claimed | Verified | Forged |
|---|---|---|---|
| Claude-User | 5,000 | 0 | 4,992 |
| ChatGPT-User | 2,670 | 13 | 2,657 |
| PerplexityBot | 2,038 | 0 | 846 |
| ClaudeBot | 4,301 | 1,070 | 852 |
| Google-Extended | 879 | 0 | 747 |
| GPTBot | 1,864 | 766 | 1,098 |
About 83% of AI-labelled traffic was not from the vendor it named.
The forgeries shared infrastructure: roughly 100 Google Cloud hosts
rotating through six vendor identities, sometimes within the same hour.
Their requests went to /.env, /terraform.tfstate,
/serviceAccountKey.json, /.env.prod.bak — credential harvesting
wearing a crawler's name.
The genuine crawlers behaved completely differently: 2,682 requests,
zero robots.txt violations, no repository source fetched, ~125 MB
total. Mostly they re-read robots.txt and sitemap.xml.
That gap is the point. Counting by user-agent tells you AI crawlers are hammering your server. Counting by verified IP tells you they are not, and that something else is — which is a different problem with a different fix.
How verification works
Most major vendors publish their crawler IP ranges as JSON. A request counts as legitimate only when its source address falls inside the range list belonging to the vendor its user-agent names.
| Vendor | Endpoint |
|---|---|
| OpenAI | openai.com/{chatgpt-user,gptbot,searchbot}.json |
| Anthropic | claude.com/crawling/bots.json |
developers.google.com/static/crawling/ipranges/*.json |
|
| Perplexity | perplexity.ai/perplexitybot.json |
| Apple | search.developer.apple.com/applebot.json |
Meta, ByteDance, Amazon and You.com publish no range file. Those are checked by forward-confirmed reverse DNS instead: the address's PTR record must end in a vendor domain, and that hostname must resolve back to the same address. The forward step is what makes it evidence — a PTR alone is written by whoever controls the address block.
| Bot | rDNS suffix |
|---|---|
| Amazonbot | .crawl.amazonbot.amazon |
| meta-externalagent, FacebookBot | .facebook.com, .fbsv.net |
| YouBot | .search.you.com |
| Bytespider | .bytedance.com, .byteoversea.com |
| PetalBot | .petalsearch.com, .aspiegel.com |
| DuckAssistBot | .duckduckgo.com |
Diffbot, Cohere and Common Crawl publish neither ranges nor a documented rDNS convention; they appear in the user-agent tally only.
Why there is no ASN verification
ASN was considered and rejected. It looks like verification but is not:
on the sample instance, genuine YouBot (68.67.112.227) and genuine
Amazonbot (100.24.167.60) both resolve to AS14618, Amazon — the
same ASN as every EC2 instance on the internet, including any spoofer
renting one. An ASN match proves the traffic came from a cloud
provider, not from the vendor. Reporting that as "verified" would be
worse than reporting nothing.
Ranges are fetched at run time and cached. If a vendor endpoint is unreachable the script falls back to the cache and says so in the mail, so an outage degrades the report instead of breaking it.
Requirements
- Traefik writing an access log with the User-Agent header kept —
it is dropped by default. See
traefik-accesslog.yml; without it nothing here works. - Python 3.9+
- An SMTP account, or a Forgejo/Gitea container whose
app.ini[mailer]section the script can borrow credentials from.
Install
sudo install -m755 crawler-alert.py /usr/local/bin/
sudo cp crawler-alert.env.example /etc/crawler-alert.env
sudo editor /etc/crawler-alert.env # set CRAWLER_RECIPIENT
sudo cp crawler-*.service crawler-*.timer /etc/systemd/system/
sudo systemctl daemon-reload
sudo systemctl enable --now crawler-alert.timer crawler-weekly.timer
Check it against your own log before enabling the timers:
CRAWLER_LOG='/var/log/traefik/access.log*' crawler-alert.py --weekly --dry-run
--dry-run prints the mail instead of sending it and needs no SMTP
config, so it is safe to run repeatedly while you tune things.
Configuration
All settings are environment variables, read from
/etc/crawler-alert.env by the systemd units. Only CRAWLER_RECIPIENT
has no default.
| Variable | Default | Meaning |
|---|---|---|
CRAWLER_RECIPIENT |
(required) | Where reports are mailed |
CRAWLER_SITE |
this site |
Name shown in subject/header |
CRAWLER_LOG |
/var/log/traefik/access.log* |
Log glob |
CRAWLER_ROUTER |
(empty) | Traefik router to count, e.g. forgejo@docker. Empty counts everything |
CRAWLER_THRESHOLD |
100000 |
Daily alert fires above this |
CRAWLER_CACHE |
/var/cache/crawler-alert/ranges.json |
Cached ranges |
CRAWLER_MAIL_CONTAINER |
forgejo |
Container to read SMTP from |
CRAWLER_MAIL_INI |
/data/gitea/conf/app.ini |
Path inside it |
CRAWLER_SMTP_* |
(unset) | Configure SMTP directly instead |
Set CRAWLER_THRESHOLD near your normal peak. Far above it, the alert
never fires and is not a tripwire — run --dry-run for a few days and
pick a number a busy day would actually reach.
Modes
crawler-alert.py # daily: mail only if over threshold
crawler-alert.py --weekly # 7-day summary, always mails
crawler-alert.py --dry-run # print instead of mailing
Only --weekly fetches ranges; the daily check needs no network.
Sample output
==============================================================
LEGITIMATE CRAWLERS (source IP inside vendor's published ranges)
==============================================================
bot verified spoofed via CF IPs
ChatGPT-User 0 561 0 0
ClaudeBot 222 161 0 14
OAI-SearchBot 23 209 0 14
GPTBot 34 196 0 2
PerplexityBot 0 196 0 0
1909 requests claimed an AI-bot identity; 323 verified (16.9%).
1586 failed IP verification (spoofed). 0 arrived via Cloudflare
and cannot be verified by IP - not counted either way.
Top paths fetched by verified crawlers:
117 /robots.txt
73 /sitemap.xml
13 /explore/repos
Limitations
Cloudflare-proxied requests cannot be verified. If traffic reaches
Traefik through Cloudflare, the logged address is Cloudflare's edge and
not the client. Those hits go in a separate via CF column rather than
being guessed at. traefik-accesslog.yml shows how to recover real
client IPs with forwardedHeaders.trustedIPs.
Some vendor lists are stale. Perplexity's has 8 prefixes and was last updated in February 2025; Apple's dates to 2023. Genuine traffic from those two may fail verification. A 0% verified rate for a small vendor is weaker evidence than it looks.
Private source addresses cannot be judged at all. If the logged
client IP is RFC1918 (172.18.0.1, a Docker bridge gateway, say), then
something in front of Traefik replaced the real address before it was
written. Those hits are counted in a private column, neither verified
nor spoofed. On the sample instance this was 21,624 of Meta's 21,651
requests — the tool cannot tell you whether they were genuine, only
that the log does not contain the evidence. Fixing it is a Traefik
forwardedHeaders change, not a script change.
rDNS is rate-limited by design. Each unique address costs two DNS
lookups, so only the busiest CRAWLER_RDNS_MAX (default 400) addresses
per bot are resolved; the rest are reported as unresolved. Raise it if
your DNS resolver is fast and local.
IPv6 is verified only where vendors publish v6 prefixes, which most do; addresses outside those are treated as unverified.
This is a reporting tool, not an enforcement one. It tells you what
happened. Blocking is a separate decision, and robots.txt only works
on the bots that already respect it — which, per the numbers above, are
exactly the ones not causing the load.
License
0BSD — see LICENSE. Do what you like with it.