How our free tools work
SimpleVerifier’s 150 free tools work in one of three ways: in your browser, so nothing you paste leaves your device; as public DNS lookups run from our server; or as a short SMTP conversation that asks a mail server about one address and disconnects before anything is sent. Each tool page says which, and cites the standard or provider document it follows.
Which tools run in my browser?
The list, phone and calculator tools run entirely in your browser. Extracting, deduplicating, filtering and formatting are text processing, so there is no reason to upload anything: the JavaScript on the page does the work and the result never reaches us. Spreadsheets are opened with your browser’s own decompression, and PDFs with Mozilla’s open-source PDF.js, loaded only when you open a PDF. These pages say “Runs in your browser” under the tool.
What happens when a tool looks up a domain?
The DNS tools (MX, SPF, DKIM, DMARC, BIMI, PTR, blocklists, provider lookup, the bulk sender checks) query public DNS from our server and read the records back, the same answers dig or nslookup would give you. Blocklist checks follow the DNSBL convention in RFC 5782. Domain age comes from the registry’s RDAP record. Nothing is sent to the domain itself.
How does the mailbox check work?
The email checker and the catch-all checker connect to the domain’s mail server and go as far as the RCPT TO step defined in RFC 5321, then disconnect. No message is delivered. Anything the server will not confirm, including catch-all domains and servers that defer, comes back as risky rather than valid. These checks are rate-limited per IP because port 25 connections are a shared resource.
Where does the reference data come from?
Phone tools use Google’s open-source libphonenumber numbering-plan metadata. It says whether a number can exist and what its range is allocated for; it cannot say whether a line is in service, and no page claims it does. Sender requirements are read from Google’s, Yahoo’s and Microsoft’s own published guidance, and record syntax from the RFCs. The disposable domain list is our own curated list, published in full. Calculators show their formula so you can check them.
We do not publish ratings, reviews or usage counts for the tools, and we do not invent benchmark figures. Where a page uses a rule of thumb rather than a published limit, it says so.
How are the pages kept current?
Every tool page shows a “Last updated” date, which changes only when the content does: a provider changes its rules, a standard is revised, or the tool changes how it works. Pages are written and reviewed by the SimpleVerifier Team. If you find something wrong, email support@simpleverifier.com and we will correct it. More on how we write in About SimpleVerifier.