vacant

Fast domain availability checker. Asks authoritative TLD nameservers directly instead of hammering WHOIS, with a built-in rules engine for things WHOIS won't tell you (no 2-letter .eu domains, registry suffixes, malformed inputs, etc.).

$ vacant anthropic.com testdomain.com3d ab.eu
{"domain":"anthropic.com","status":"registered"}
{"domain":"testdomain.com3d","status":"invalid"}
{"domain":"ab.eu","status":"reserved"}

Install

brew install alltuner/tap/vacant
# or
cargo install vacant

Usage

# single domain
vacant example.com

# many at once (positional, or one per line on stdin)
vacant a.com b.net c.org
cat domains.txt | vacant

# pretty table output
vacant -o table example.com

# include zone, raw input, detail, cache hit
vacant --detail example.com

# only show available results
vacant --available a.com b.com c.com

# tighten timeout, raise concurrency for large batches
vacant --timeout 2 --concurrency 256 < big-list.txt

Exit codes: 0 on success, 2 if any result has status=unknown (transport failure, ambiguous registry response).

How it works

For each input:

1. Rule layer rejects malformed strings (empty labels, no TLD), unknown TLDs (not in the bundled Public Suffix List), per-zone violations (e.g. .eu minimum 3 characters), and registry suffixes used as inputs (co.uk is not a registrable name).
2. Authoritative NS query against the parent zone's nameservers, with +norecurse. NS delegation present → registered. NXDOMAIN → available.
3. RDAP fallback for registries that use compact denial of existence (Nominet .uk, several others) where step 2 returns NODATA.

Per-host nameserver cooldowns (5 min after a transport failure) and per-RDAP-host throttling (2 concurrent + 100ms gap) keep things polite under heavy use.

Bundled data

data/rules.toml ships baked into the binary at compile time. It carries:

• The Public Suffix List ICANN section (~6900 zones)
• IANA RDAP bootstrap URLs per TLD
• Hand-curated per-zone overrides (length limits, character classes, etc.)

CI refreshes it weekly via ingest/psl.py and ingest/rdap.py (PEP 723 inline-deps scripts; run with uv run ingest/psl.py). Override the bundled file at runtime with --rules path/to/rules.toml or VACANT_RULES=....

Develop

just              # menu
just build        # cargo build --release
just test         # cargo nextest / cargo test
just check        # fmt + clippy
just ingest-psl   # refresh PSL data (writes data/rules.toml)
just ingest-rdap  # refresh RDAP bootstrap (writes data/rules.toml)

Etiquette

You're querying TLD operators (Verisign for .com/.net, Nominet for .uk, etc.) directly. Sporadic interactive use is invisible noise to them; sustained high-rate scanning would be impolite. The built-in cache (1-day TTL by default) and per-host backoff are there to keep you well-behaved automatically.

License

MIT. See LICENSE.