Carrier-filtered, de-duplicated and verified on your own machine — before a single paid lookup is spent.
Most tools validate first and filter after — so you pay to check numbers you were always going to bin. List Viper runs it backwards. Four free layers strip the list down, and only the survivors ever reach a billable lookup.
Two million prefixes from the public numbering plan, compiled into a flat 20 MB array. Line type resolves in one indexed read. No network, no per-row fee, no ceiling.
One bit per possible number, allocated lazily. Exact rather than hashed — it can never produce a false match — and flat in memory whether the file is 20 MB or 20 GB.
Every answer you buy is kept for good. Lists overlap month to month, so the second run over the same data is mostly free and the tenth is almost entirely free.
That file had 7,151,542 rows of landline, VoIP and duplicates struck out before a single credit was spent. At the $0.022 a lookup the validation services charge, that is what one run saved. The Solo licence costs less than one per cent of the savings from that single run — and you own it afterwards.
Import the free NANPA block table — a few seconds on first run — then untick Landline and VoIP under Carriers and run Clean & filter. The table covers over two million NPA‑NXX prefixes and gives you the line type of every number without a single paid lookup. On a real 209-million-row archive it identified roughly a third of the surviving numbers as landline or VoIP.
No, and avoiding that is the point of the tool. Carrier resolution runs in four steps, cheapest first: your own verified cache, then the free block table, then the vendor’s carrier column if the file came with one, and only then a paid lookup — on distinct numbers only, and only on what survived every free filter above. Every paid answer is cached forever, so the same number is never bought twice.
There is no size limit. Files are streamed from disk rather than loaded into memory, so memory stays flat as the file grows. The largest measured run was 209,024,147 rows across 208 files and 26 GB, finished in a single pass in about two hours on an external USB drive.
No. Your lists are read off your disk and written back to it — no upload, no account, no cloud storage. The only things that ever leave the machine are a phone number when you ask to buy a lookup for it, and a once-daily licence check-in carrying a licence ID, an anonymous machine fingerprint and a version number. No names, no lists, no rows.
By storing one bit per possible number instead of the numbers themselves. A set holding a hundred million numbers would want north of 6 GB; a bitmap indexed by phone number, allocated lazily in blocks, stays close to a gigabyte however long the file is.
The block table is reliable for line type — wireless, landline,
VoIP — and only approximate for brand, because porting moves a number
between carriers without changing the block it was issued from. Use it to strike
landlines and VoIP with confidence. For verified brand, use the cache or a paid
lookup; every output carries a carrier_source column so a verified answer
is never confused with a block-table guess.
Two, and they are separate accounts with separate billing. IPQualityScore for phone validation, line status, prepaid, do-not-call, abuse history and fraud score. Blacklist Alliance for litigator scrub against known TCPA litigators and serial filers. Both are inert until you enter your own API key, and neither can spend the other’s balance.
CSV, TXT or any delimited text. Comma, tab, pipe and semicolon delimiters are detected automatically, as are UTF‑8, UTF‑8 with BOM, Windows‑1252 and Latin‑1 encodings. The phone column is found by the shape of the numbers rather than the header text, so unlabelled columns still work.
No. $497 once for one machine, $997 for five. The licence is perpetual and the software never stops working. Twelve months of updates are included; after that the version you have carries on exactly as it is, and newer versions are optional at $197 a year.
Not currently. List Viper is a Windows application, tested on Windows 10 and Windows 11. It installs for you alone and needs no administrator rights.
Windows installer, 21 MB. Installs for you alone — no admin rights needed. Full product for seven days, 250,000 rows a run.
Download for Windows →Pay once and it is yours for good. Card, bank, Cash App, Klarna or Amazon Pay. Your licence key is emailed to you the moment the payment clears — instantly on a card, and the day it settles if you pay by bank.
No upload. No account. No cloud bucket. No telemetry. Your lists are read off your disk and written back to it, and nothing else ever sees them.
Two things do leave, and it is worth saying exactly what. A phone number, when you ask to buy a lookup for it — that is the lookup. And once a day, a licensed copy reports its licence ID, an anonymous machine fingerprint and the version number, so a key that was refunded or passed around can be switched off. No names, no lists, no rows. If that report never gets through, nothing stops working — the licence is verified offline by signature, and the check-in is only ever advisory.
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