--- title: "LookValid blog" url: "https://lookvalid.com/blog.md" canonical_url: "https://lookvalid.com/blog" last_updated: "2026-10-19" type: "index" summary: "Sourced guides on phone, email, IP and domain checks, fraud signals and the LookValid API, each with working code or a table of our own." related: ["https://lookvalid.com/docs.md", "https://lookvalid.com/help.md"] --- # LookValid blog Sourced guides on phone, email, IP and domain checks, fraud signals and the LookValid API, each with working code or a table of our own. ## Security - [A checklist for SPF, DKIM and DMARC records](https://lookvalid.com/blog/security/spf-dkim-dmarc-checklist.md): 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](https://lookvalid.com/blog/security/stop-fake-signups-with-layered-checks.md): 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](https://lookvalid.com/blog/security/spotting-fake-phone-numbers.md): 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](https://lookvalid.com/blog/security/proxy-and-vpn-detection-limits.md): 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](https://lookvalid.com/blog/security/dmarc-enforcement-gap-explained.md): 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](https://lookvalid.com/blog/security/link-safety-checks-before-you-click.md): 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](https://lookvalid.com/blog/security/why-calls-show-as-spam-likely.md): 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](https://lookvalid.com/blog/security/young-domains-as-fraud-signal.md): 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 - [A step by step order for cleaning an email list](https://lookvalid.com/blog/technical/email-list-cleaning-steps.md): 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](https://lookvalid.com/blog/technical/catch-all-email-domains-explained.md): 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](https://lookvalid.com/blog/technical/hlr-lookup-explained-and-its-alternatives.md): 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](https://lookvalid.com/blog/technical/mcp-or-rest-for-lookups.md): 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](https://lookvalid.com/blog/technical/phone-number-formats-and-e164.md): 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](https://lookvalid.com/blog/technical/rdap-and-whois-domain-registration-data.md): 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](https://lookvalid.com/blog/technical/bulk-validation-with-csv-jobs.md): 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](https://lookvalid.com/blog/technical/mobile-landline-and-voip-line-types.md): 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](https://lookvalid.com/blog/technical/reading-robots-txt-sitemaps-and-llms-txt.md): 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](https://lookvalid.com/blog/technical/ip-geolocation-accuracy-and-limits.md): 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 - [A sending-domain checklist for agency clients](https://lookvalid.com/blog/industry/cold-email-agency-deliverability-checklist.md): 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](https://lookvalid.com/blog/industry/domain-authority-for-link-prospecting.md): 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](https://lookvalid.com/blog/industry/enrich-b2b-contacts-from-public-pages.md): 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](https://lookvalid.com/blog/industry/phone-checks-for-voice-agents.md): 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](https://lookvalid.com/blog/industry/cold-email-software-evaluation-criteria.md): 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](https://lookvalid.com/blog/industry/ai-sdr-data-quality.md): 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](https://lookvalid.com/blog/industry/what-makes-an-email-address-valid.md): 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 - [Build a small MCP server in TypeScript](https://lookvalid.com/blog/tutorial/build-an-mcp-server-typescript.md): 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](https://lookvalid.com/blog/tutorial/bulk-validate-csv-in-python.md): 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](https://lookvalid.com/blog/tutorial/disposable-email-detection-api-tutorial.md): 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](https://lookvalid.com/blog/tutorial/check-an-ip-in-express-middleware.md): 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](https://lookvalid.com/blog/tutorial/connect-lookvalid-to-claude-over-mcp.md): 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](https://lookvalid.com/blog/tutorial/decode-a-vin-with-an-api.md): 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](https://lookvalid.com/blog/tutorial/scrape-contact-details-from-a-website-api.md): 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](https://lookvalid.com/blog/tutorial/validate-phone-numbers-python-api.md): 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](https://lookvalid.com/blog/tutorial/nodejs-email-domain-verification.md): 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 - [Free lookup tools that need no account](https://lookvalid.com/blog/product/free-tools-without-an-account.md): 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](https://lookvalid.com/blog/product/how-credits-and-success-billing-work.md): 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](https://lookvalid.com/blog/product/introducing-lookvalid.md): 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. ## Related - [Documentation](https://lookvalid.com/docs.md) - [Help center](https://lookvalid.com/help.md)