domain-checker

Domain Checker

Check domain availability in bulk using RDAP (Registration Data Access Protocol) as the primary signal, with WHOIS and DNS fallbacks. Python stdlib only.

When to Use

• User asks "is <domain> available / taken / registered?"
• User wants to check many domains at once (a list, a file, names piped in)
• User wants to test a brand name across many TLDs (acme.com, acme.net, acme.io, …)
• User wants machine-readable output (CSV/JSON) for further processing
• User wants only available (or only taken) results filtered

Do NOT use for: WHOIS contact lookup (this skill only checks existence), DNS record inspection (use dig), trademark/legal availability (this only checks registration status).

How It Works

1. RDAP first — fetches the IANA RDAP bootstrap (data.iana.org/rdap/dns.json, cached 24h in ~/.cache/domain-checker/) to find the authoritative RDAP server for each TLD. HTTP 404 = available, HTTP 200 = taken.
2. WHOIS fallback — if RDAP is unavailable for a TLD (notably .io, some ccTLDs) or returns ambiguous, shells out to the local whois CLI and matches well-known "not found"/"registered" patterns.
3. DNS — optional, weak signal. Resolves A/AAAA records. Confirms "taken" only — registered-but-unhosted domains will show no DNS, so DNS alone cannot prove "available".

After the primary check, three enrichment passes refine accuracy:

1. Aftermarket detection — parses the RDAP response we already fetched. Flags aftermarket when the registrant/entity name matches a known reseller (HugeDomains, Sedo, Afternic, Dan.com, NameJet, DropCatch, …) OR when the nameservers match parking patterns (sedoparking.com, parkingcrew.net, namefind.com, afternic.com, bodis.com, …). Free — no extra requests.
2. RDAP status parsing — surfaces pendingDelete / redemptionPeriod / clientHold / serverHold as a separate expiring status (these domains may drop and become available within ~30 days).
3. Premium-likely hint — for available results, appends a warning when the name is short (≤5 chars on .ai/.io/.app/.dev/.co/.tv/.me/.cc/.tech/.xyz or ≤3 chars on .com/.net/.org). This is a heuristic, not a hard claim — the registrar checkout has the real price.
4. Optional HTTP sale-page probe (--probe-sale) — fetches the homepage and looks for "for sale" / Sedo / Dan.com / HugeDomains / Afternic markers. Reclassifies taken → aftermarket on a hit. Off by default; adds ~1s per checked domain.

Concurrency via ThreadPoolExecutor (default 10 workers). Per-request timeout default 8s.

Prerequisites

• Python 3.8+ (stdlib only)
• Outbound HTTPS to RDAP servers
• Optional: whois CLI (brew install whois / apt install whois) for fallback on TLDs without RDAP

Quick Routing

| Task | Command | |------|---------| | Check single domain | check_domains.py acme.com | | Check many domains | check_domains.py acme.com acme.net acme.io | | Bare name across TLDs | check_domains.py acme --tlds com,net,io,ai,dev | | From a file | check_domains.py --file domains.txt | | From stdin | cat list.txt \| check_domains.py --stdin | | Only available | check_domains.py --file list.txt --only-available | | JSON output | check_domains.py acme.com --format json | | CSV output | check_domains.py acme.com --format csv | | Force WHOIS only | check_domains.py acme.io --method whois | | Fastest (DNS only) | check_domains.py acme.com --method dns |

Usage

python3 .claude/skills/domain-checker/scripts/check_domains.py [DOMAINS...] [OPTIONS]

Examples

# Single domain
python3 scripts/check_domains.py google.com

# Many domains
python3 scripts/check_domains.py acme.com acme.net brandidea.io

# Brand-name search across TLDs
python3 scripts/check_domains.py mybrand --tlds com,net,io,ai,dev,app

# From a file (one domain per line, # comments allowed)
python3 scripts/check_domains.py --file domains.txt

# From stdin
printf 'foo.com\nbar.io\n' | python3 scripts/check_domains.py --stdin

# Only available, as CSV (great for piping into a sheet)
python3 scripts/check_domains.py --file candidates.txt --only-available --format csv > available.csv

# JSON for programmatic use
python3 scripts/check_domains.py acme --tlds com,net,io --format json

# Higher parallelism for big lists
python3 scripts/check_domains.py --file 500-domains.txt -c 25

# Exit code reflects unknown/invalid results (for CI)
python3 scripts/check_domains.py --file list.txt --exit-code

Output

Default table format:

   domain         status        method  evidence                                                    ms
-  -------------  ------------  ------  ----------------------------------------------------------  ----
✓  acme.dev       available     rdap    RDAP 404 from https://pubapi.registry.google/rdap           437
✓  bzqj.dev       available     rdap    RDAP 404 …; likely premium tier (.dev <=5 chars)            383
✗  google.com     taken         rdap    RDAP 200 from https://rdap.verisign.com/com/v1              333
$  foothill.com   aftermarket   rdap    RDAP 200 …; parking NS: ns1.afternic.com                    352
~  someone.com    expiring      rdap    RDAP 200 …; status: pendingdelete                           340
?  bizarre.tld    unknown       rdap    no RDAP server for .tld                                     12
!  bad..domain    invalid               invalid domain syntax                                       0

| Symbol | Status | Meaning | |--------|--------|---------| | ✓ | available | No registration record found (RDAP 404 or WHOIS no-match) | | ✗ | taken | Domain is registered (legit ownership) | | $ | aftermarket | Registered but held by a domain investor / parking service — usually for resale at premium prices | | ~ | expiring | Registered but in pendingDelete / redemptionPeriod / clientHold — may drop and become available | | ? | unknown | Neither method could decide (rate-limited, no RDAP server, etc.) — retry, or use a registrar to confirm | | ! | invalid | Domain syntax invalid | | · | reserved | TLD-reserved (rare, e.g. some registry-internal names) |

For available results, the evidence column may include likely premium tier (...) — a heuristic warning that the registry probably charges a premium for this short name on this TLD.

Flags

| Flag | Default | Description | |------|---------|-------------| | positional DOMAINS | — | Zero or more domains or bare names | | -f, --file PATH | — | Read domains from file (one per line, # comments OK) | | --stdin | off | Read domains from stdin | | --tlds com,net,... | — | TLDs to append to bare names (only used for inputs without a .) | | -m, --method | auto | auto (rdap→whois), rdap, whois, dns, or comma list | | -c, --concurrency N | 10 | Parallel workers | | -t, --timeout S | 8.0 | Per-request timeout, seconds | | --format | table | table, json, or csv | | --only-available | off | Filter output to available only | | --only-taken | off | Filter output to taken / aftermarket / expiring | | --no-color | off | Disable ANSI colors in table output | | --no-aftermarket-detect | off | Skip RDAP entity / nameserver analysis (faster, less accurate) | | --no-premium-hint | off | Don't warn on short available names | | --probe-sale | off | HTTP-probe taken domains for "for sale" landing pages (~1s/domain) | | --exit-code | off | Exit non-zero if any unknown/invalid result (useful in CI) |

--only-available and --only-taken are mutually exclusive (last one wins).

Method Notes

| Method | Pros | Cons | |--------|------|------| | rdap | Standardized JSON; works for nearly all gTLDs; fast; no parsing fragility | Some ccTLDs (.io, .co.uk, …) don't expose RDAP | | whois | Covers TLDs without RDAP | Output format varies per registry; rate-limited; requires CLI installed | | dns | Very fast | Cannot prove "available" — registered-but-unhosted domains have no DNS | | auto (default) | RDAP first, WHOIS fallback when RDAP is unavailable/inconclusive | Slightly slower on TLDs that need fallback |

Improving Accuracy

Default mode already runs aftermarket detection + premium hints (no extra cost — they reuse the RDAP response). For maximum accuracy on important brand searches, add --probe-sale:

python3 scripts/check_domains.py mybrand --tlds com,net,io,ai,dev --probe-sale

What each enrichment catches:

| Enrichment | Detects | Cost | |------------|---------|------| | Aftermarket via RDAP entities | HugeDomains / Sedo / Afternic / Dan.com / NameJet etc. as the registrar or registrant | Free — re-uses RDAP response | | Aftermarket via parking nameservers | afternic.com, sedoparking.com, parkingcrew.net, namefind.com (GoDaddy investor portfolio), bodis.com, dan.com, hugedomains.com | Free | | RDAP status parsing | pendingDelete / redemptionPeriod / clientHold | Free | | Premium-likely hint | ≤5 chars on .ai/.io/.app/.dev/.co/.tv/.me/.cc/.tech/.xyz; ≤3 chars on .com/.net/.org | Free (local) | | --probe-sale HTTP fetch | "For sale" landing pages (Sedo, Dan.com, HugeDomains, GoDaddy Auctions, Afternic) | ~1s/domain |

What this can't catch

| Limitation | Why | |------------|-----| | Exact premium price | No free API exposes registry-tier pricing. Always check the registrar checkout. | | Trademark conflicts | Requires USPTO TESS / WIPO lookups (out of scope). | | Privately-held investor domains | Brokers using cloaked WHOIS + non-parking nameservers (e.g. Cloudflare) will look like normal "taken" — only --probe-sale can sometimes catch these via the landing page. | | Domains in pendingCreate / about to register | RDAP shows them as available; you'll race the registrant at checkout. |

Caching

The IANA RDAP bootstrap is cached for 24 hours at:

~/.cache/domain-checker/rdap-bootstrap.json

Delete that file to force a refresh.

Limitations

• Rate limits: registry RDAP servers will rate-limit aggressive bulk checks. For lists >200 domains, consider -c 5 and reasonable spacing.
• Truth-source: a domain marked available here may still be unregisterable (premium, reserved by registry, or held in pending-delete). Always confirm at the registrar checkout.
• Privacy: every RDAP/WHOIS query is logged by the registry. Don't bulk-check competitor brand lists from infrastructure you don't want associated with the queries.
• No registrar pricing: this skill only reports availability — pricing varies wildly across registrars and is not queried.

See Also

• references/tlds.md — common TLDs and which method works best for each