Free Web Diagnostic Tools
Free IP · DNS · SSL · email · SEO checks. No sign-up, instant in your browser.
Network / IPDNS / DomainTLS / CertificatesEmailWeb SecurityHTTP / APISEO / IndexingPerformance / FrontendWordPress / CMSCDN / CloudOps / SREAdSense / Monetization
90 tools · no sign-up · 100% free
IP, DNS, SSL/TLS, email, security, SEO and performance checks in one place. Free diagnostic tools for webmasters, developers and operators.
Network / IP
13 toolsCIDR Calculator
Calculate IP range, subnet mask and host count from CIDR notation.
IPv6 Compress / Expand
Convert IPv6 addresses between compressed and expanded forms.
Public / Private IP Checker
Check whether an IP is private, loopback or a reserved range.
IP Range to CIDR
Convert a start and end IP into the minimal set of CIDR blocks.
MTU / MSS Calculator
Calculate recommended MTU and MSS for tunnels, VPN and PPPoE.
What Is My IP
Show your current public IP address and connection details.
IP / ASN Lookup
Look up an IP's owning org, ASN and allocation via RDAP.
IP Geolocation Lookup
Look up an IP's country, city, ISP and ASN.
Website IP Address Lookup
Find the IPv4/IPv6 server address a domain points to.
MAC Address Lookup
Identify the device vendor from a MAC address prefix (OUI).
Subnet Splitter (VLSM)
Split one IP block into multiple smaller subnets and list each range and host count.
IPv4 ↔ IPv6 Mapping
Convert an IPv4 address to IPv4-mapped/compatible IPv6 forms and back.
Ping Result Analyzer
Parse pasted ping output for packet loss and min/avg/max latency, with interpretation.
DNS / Domain
9 toolsDomain Status Code Decoder
Explain EPP domain status codes like clientTransferProhibited.
DNS Change Impact Checklist
Check risks before changing NS, MX or TXT records.
Typosquatting Domain Generator
Generate look-alike and typo domains for phishing/brand protection.
DNS Record Lookup
Look up A, AAAA, MX, TXT, NS, CNAME and SOA records for a domain.
DNS Propagation Check
Compare a record across multiple public resolvers to check propagation.
Reverse DNS (PTR) Lookup
Look up the hostname (PTR record) for an IP address.
WHOIS / Domain Lookup
Look up a domain's registrar, dates and status via RDAP.
Nameserver (NS) Check
Look up a domain's nameservers and check their consistency.
DNSSEC Checker
Check whether a domain has DNSSEC (DS/DNSKEY) enabled.
TLS / Certificates
6 toolsSSL Error Message Decoder
Explain browser SSL errors like ERR_CERT_COMMON_NAME_INVALID.
CAA Record Check
Check which CAs are allowed to issue certificates via CAA records.
SSL Certificate Checker
Check a domain's SSL certificate expiry, issuer, chain and TLS version live.
TLS Version Check
Check which TLS versions (1.0–1.3) a server supports and grade safety.
SSL Certificate Decoder
Paste a PEM certificate to decode subject, issuer, validity and SANs.
CSR Decoder
Paste a CSR to decode its subject and key information.
Email Bounce Code Decoder
Explain 4xx/5xx SMTP bounce codes and how to fix them.
Email Header Analyzer
Analyze mail headers: hops, delays and SPF/DKIM/DMARC results.
DMARC Record Generator
Generate a DMARC TXT record from policy and report settings.
SPF Record Lookup
Look up a domain's SPF TXT record and check syntax.
DMARC Record Lookup
Look up the _dmarc TXT record and explain its policy and tags.
DKIM Record Lookup
Look up the selector._domainkey TXT record for a DKIM public key.
Email Blacklist (DNSBL) Check
Check whether an IP is listed on major DNSBL blacklists.
Email Deliverability Check
Check a domain's MX, SPF, DKIM, DMARC and blacklists at once.
SPF Lookup Counter
Count a domain's SPF DNS lookups and flag the 10-lookup limit.
BIMI Record Checker
Check the BIMI TXT record and its logo/certificate declarations.
Email Address Validator
Validate an email address format and check the domain's MX records.
Web Security
10 toolsCSP Generator
Build a Content-Security-Policy header for your site's resources.
SRI Hash Generator
Generate Subresource Integrity hashes for external JS/CSS.
Password Policy Generator
Generate a password policy and its rules for your service.
Security Headers Checker
Check and grade security headers like HSTS, CSP and X-Frame-Options.
Cookie Security Check
Check Secure, HttpOnly and SameSite flags on response cookies.
security.txt Checker
Check for /.well-known/security.txt and its required fields.
Mixed Content Checker
Find insecure http resources loaded on an HTTPS page.
Permissions-Policy Builder
Pick browser feature permissions (camera, geolocation, mic…) to build a Permissions-Policy header.
Referrer-Policy Recommender
Recommend a Referrer-Policy value for your site type and compare how each value behaves.
SameSite Cookie Matrix
See how SameSite=Strict/Lax/None behave across cross-site flows like login and checkout.
HTTP / API
8 toolscURL Command Builder
Build a runnable cURL command from method, headers and body.
cURL Command Parser
Break a cURL command into method, URL, headers and body.
Latency Percentile Calculator
Compute p50, p90, p95 and p99 from a list of response times.
HTTP Header Checker
Fetch and display the HTTP response headers of a URL.
HTTP Status & Redirect Checker
Trace the HTTP status code and full redirect chain step by step.
HTTP/2 & HTTP/3 Check
Check whether a server supports HTTP/2 (ALPN) and HTTP/3 (Alt-Svc).
CORS Configuration Check
Check a URL's CORS (Access-Control-Allow-*) headers via preflight.
API Rate Limit Calculator
Calculate safe call volume and burn-down time from per-minute/hour limits and concurrency.
SEO / Indexing
13 toolsMeta Title Length Checker
Check title length and how it fits in search results.
Meta Description Length Checker
Check description length and search snippet fit.
SERP Snippet Preview
Preview how your title, URL and description appear in Google results.
Structured Data Generator
Generate Schema.org JSON-LD for Article, FAQ, Breadcrumb and more.
robots.txt Generator
Generate a robots.txt with allow/disallow rules and sitemap.
hreflang Tag Generator
Generate hreflang link tags for multilingual pages.
Open Graph Tag Generator
Generate Open Graph and Twitter card meta tags.
Open Graph Preview
Fetch a URL's OG/Twitter meta tags and preview the share card.
robots.txt Checker
Fetch a site's robots.txt and review its rules and sitemap declarations.
SEO Meta Tag Checker
Fetch and check a URL's title, description, canonical, OG and h1.
Sitemap Validator
Fetch sitemap.xml and validate format, URL count and index files.
Favicon Checker
Check a site's favicon, icons and web manifest declarations.
URL Slug Checker
Check a URL slug for length, special characters, uppercase and spaces, and suggest a clean slug.
Performance / Frontend
6 toolsImage Format Recommender
Recommend the right image format (WebP, AVIF, PNG, JPEG) for your use case.
Cache-Control Builder
Build a Cache-Control header for your resource type.
Resource Hints Generator
Generate preload, preconnect and dns-prefetch link tags.
Response Time Test
Measure a URL's server response time and redirect overhead.
Compression (gzip/brotli) Check
Check whether the server applies gzip/brotli compression and the savings.
Page Weight Analyzer
Analyze a page's HTML size and the count/type of referenced resources.
WordPress / CMS
2 toolsCDN / Cloud
2 toolsOps / SRE
6 toolsUptime SLA Calculator
Compute allowed downtime per period for 99%–99.999% SLAs.
Cron Next Run Calculator
Show the next run times for a cron expression.
Log Timestamp Converter
Convert epoch/ISO timestamps to KST, UTC and local time.
Bandwidth Cost Calculator
Estimate monthly bandwidth/CDN cost from traffic and unit price.
Downtime Cost Calculator
Estimate the cost of an outage from hourly revenue, conversion rate and downtime duration.
Server RAM Calculator
Estimate the RAM a web server needs from concurrency, worker count and per-process memory.
AdSense / Monetization
4 toolsUTM Builder
Build trackable UTM URLs from campaign source, medium and name.
UTM Parser
Extract and break down UTM parameters from a long URL.
AdSense RPM Calculator
Estimate RPM and revenue from pageviews, CTR and CPC.
Pageview Revenue Simulator
Reverse-calculate the pageviews, CTR and CPC needed for a target monthly income.