LookValid blog
Guides on phone, email, IP and domain checks, fraud signals and the API. Every outside claim names its source.
Security
Fraud signals, spoofing and the rules around calling and email.
A checklist for SPF, DKIM and DMARC records
Check the three email authentication records in minutes, with the RFC limits that trip people up and a request that reads SPF and DMARC for you.
Catch fake signups with three layered checks
Combine a throwaway email domain check, a domain age check and an IP hosting check to catch fake signups, with a decision table and a note on false positives.
Spotting fake phone numbers in signup forms
How fake and throwaway phone numbers show up in signup forms, which ones a numbering-plan check catches, and which ones it cannot tell from real numbers.
What an IP lookup can say about VPNs
An IP lookup can show hosting ranges and Tor exits, but not every proxy or VPN. See which fields to trust when screening signups and which to leave alone.
What DMARC none, quarantine and reject really do
A DMARC record is a request, not a lock. See what p=none, quarantine and reject ask receivers to do and why a domain with a record can still be spoofed.
What you can check about a link before opening
The parts of a URL you can inspect without visiting it, and exactly what the link-safety check covers: one published list of malicious domains.
Why a call shows as spam likely
A spam label comes from caller ID spoofing, call authentication results and call analytics. Learn what each signal means and how to read a complaint score.
Why a new domain is worth a closer look
Registration age is a cheap fraud signal. See how RDAP exposes it, how the domain-age product reads it, and a table of age bands you can adapt.
Technical
How phone, email, IP and domain checks work under the hood.
A step by step order for cleaning an email list
Clean a list in the right order: syntax, normalization, deduplication, domain checks and role accounts, with the RFC limits behind each step.
Catch-all email domains, explained
Why a mail server that accepts every recipient gives no mailbox answer, what SMTP says about it, and what a domain-level check can and cannot show.
HLR queries explained, and what to use instead
What a home location register query does on the signalling network, what it can reveal, and what numbering-plan and carrier checks tell you instead.
MCP or REST: choosing how to call a lookup
When a lookup should go through the MCP server and when through the REST API: who the caller is, auth, cost, determinism, batching and error handling.
Phone number formats and E.164, explained
How to store and validate phone numbers: E.164, country calling codes, national prefixes and extensions, with real outputs from the LookValid phone check.
RDAP versus WHOIS for domain registration data
How RDAP differs from WHOIS, how the IANA bootstrap file finds the right registry, what each registration field means, and how a domain age check reads it.
Running a large list through a lookup safely
Batch a big list through a lookup without paying twice: CSV rules, bulk job limits, cache-backed re-runs and a REST loop with retries.
What a phone number's line type tells you
Mobile, fixed line, VoIP, toll-free, premium and more: what each line type means, why some countries cannot separate them, and how porting limits a prefix.
What robots.txt, sitemaps and llms.txt do
A plain guide to four small files every site can publish, what each specification requires, and what a site files checker reports about them.
Where IP geolocation is accurate and where not
IP geolocation is an estimate, not a position. See why results vary by network, what carrier NAT and VPNs do to them, and how to read a city as a hint.
Industry
How teams use lookup data in sales, support and operations.
A sending-domain checklist for agency clients
Onboarding a client sending domain? Check SPF, DKIM, DMARC, MX, domain age and list quality against the published rules before the first send.
Domain authority scores for link prospecting
What a domain authority style score measures, what it misses, and how our domain authority lookup builds its 0 to 100 number from open data.
Enrich a company list from public pages
Build a short enrichment pipeline from what companies publish themselves: contact pages, link-in-bio pages, domain age, authority and mail setup.
Phone checks for an AI voice agent
A pre-dial gate for AI voice agents: numbering-plan validity, line type, original carrier and caller ID complaint history, with what each result means.
Testable criteria for cold email software
Seven capabilities to test before you commit to cold email software: list validation hooks, per-domain throttling, bounce handling and RFC 8058 headers.
What an AI sales agent must know before acting
Gate every step of an AI sales agent on lookup results: domain mail setup, role mailboxes, disposable domains and phone number type, with working code.
What makes an email address valid: four layers
Valid syntax, a working domain, a real mailbox and safety to send are four separate questions. See what each layer proves, with RFC references and a sample.
Tutorials
Working code for the LookValid API and the MCP server.
Build a small MCP server in TypeScript
Write a minimal MCP server in TypeScript with one tool that wraps a LookValid lookup over REST, using the official SDK as documented.
Bulk-check a CSV of IP addresses in Python
A standard-library Python script that reads a CSV, runs one IP lookup per unique row with threads paced to the API rate limit, and writes a results CSV.
Catch throwaway emails with one API call
Flag disposable email domains at signup with a short Node.js function, and learn exactly what the check reads and what it cannot see.
Check signup IPs in Express middleware
Express middleware that looks up each signup request's IP, attaches the result to the request, and keeps working when the lookup is slow or down.
Connect Claude to a lookup API over MCP
Add the LookValid MCP server to Claude Code, Cursor, VS Code or Codex with a key or OAuth, then test it from a terminal with one curl call.
Decode a VIN with an API call
How a 17-character VIN is laid out, how its check digit is worked out, and how to decode one into make, model and year with a single API request.
Scrape contact details from a website via API
Call two scraping endpoints from code: one returns emails, phones and social profiles, the other a page as text. Includes blocked-site and cost behavior.
Validate a list of phone numbers with Python
Clean and check a list of phone numbers with Python requests: normalise the input, handle errors and 429s, and read the credit fields on each result.
Verify email domains in Node.js, step by step
Call the email domain check from Node.js with fetch, handle found false, read the error envelope and retry on 429 using the rate limit headers.
Product
What we shipped and why.
Free lookup tools that need no account
Which LookValid tools run with no account, the per-visitor limits, how they relate to the API, and when it makes sense to move to an API key.
How credits and success billing work
Exactly when a LookValid lookup reserves, charges or releases credits: found, not found, cache hits, errors and timeouts, with a table of outcomes.
One API key and one balance for many lookups
What LookValid is: one key and one credit balance across phone, email domain, IP, domain and website lookups, plus free tools and an MCP server.