Domain Portfolio Check

Why I built it

Companies accumulate domains over time — the main site, typo variants, defensive registrations, country-code versions, and whatever arrived with an acquisition. In the context of an M&A transaction, someone has to run diligence on these domains to determine what is held, through whom, and whether anything is close to lapsing. This is often done with manual WHOIS lookups across various registries. Doing a manual domain lookup for a hundred or so domains could easily take several hours. This tool does that work in minutes, with literally only seconds of human effort required.

How it works

The user pastes a list of domains into the browser interface, or uploads a text or CSV file. The tool parses these inputs, using regular expressions to ensure the domains are accurate before sending them for lookup.

The lookups then run concurrently in a thread pool. Registries rate-limit bulk querying, so the concurrency is configurable, and the default is set low enough to be comfortable across a few hundred domains. A failure on one domain does not stop the run.

The underlying WHOIS library tends to return messy output. For the same conceptual field, a datetime, a list of datetimes, a bare string in one of several formats, or nothing at all, could all be returned depending on which registry answered. The tool passes every field through a coercion layer to standardize the output.

Each result is then reduced to a single status: OK, expiring within a configurable window, expired, no expiry date published, or lookup failed. Several country-code registries do not publish expiry over WHOIS at all, so these are left blank, whereas a failed lookup is worth retrying.

Output

The results table colours each row by status, and the same colouring carries into the Excel export. Below is an example run over seven domains.

How it was built

Built in Python with the help of Claude Code. Source is not public, but I am happy to walk through it.