Free online tools
Free online tools
A date calculator with an age calculator and countdown, a DNS lookup and propagation check, an SPF, DKIM and DMARC checker, a schema markup generator and more. Free, with no sign-up.
Days between dates, add or subtract time, an age calculator, a live countdown, the day of the week and ISO week numbers.
- Days between two dates, with weekdays
- Add or subtract years, months, weeks, days or business days
- Exact age and next birthday
- Countdown to any date or holiday
- Day of the week and ISO week numbers
Every DNS record for a domain, a propagation check across four resolvers, a subdomain finder and reverse IP lookup.
- A, AAAA, CNAME, MX, NS, TXT, SOA, CAA, HTTPS, SRV and DNSSEC records
- Propagation check across four public resolvers
- DNS host, email provider and web host detection
- Common subdomain finder
- Reverse lookup with forward confirmation
Score a domain’s email authentication out of 100, with SPF, DKIM, DMARC, MTA-STS and BIMI, plus SPF and DMARC generators.
- SPF, DKIM, DMARC and MX check with a score
- SPF lookup count against the limit of 10
- MTA-STS, TLS reporting and BIMI
- Gmail and Outlook.com sender rules
- SPF and DMARC record generators
JSON-LD for 13 schema.org types with a worked example for each, and a validator for the markup already on a page.
- 13 types, from Organization to Recipe
- A filled-in example for every type
- Validator for JSON-LD or full page HTML
- Copy, or download as a .json file
- Google’s required properties for each type
Quick tools
Single-purpose calculators and lookups
Exact age in years, months and days from a date of birth, and the days until the next birthday.
DatesCountdownA live countdown to any date and time, with weekdays and weekends left. Share it as a link.
DatesDay of the weekThe weekday for any date, past or future, with the ISO week and day of the year.
DatesWhat week is itThe current ISO week number and every week of the year with its dates.
DomainsMX lookupThe MX records for any domain, in priority order, with the email provider.
DomainsDNS propagation checkerCheck whether a DNS change has spread across four public resolvers.
DomainsReverse DNS lookupThe host name for an IP address from its PTR record, forward-confirmed.
More tools
Time, dates and accessibility
These run on the pages of the free MCP servers they come from.
See a time in every city you work with, with offsets, daylight saving and working hours.
DatesBusiness days calculatorWorking days between two dates, or business days added to a date, for any weekend pattern.
AccessibilityColor contrast checkerCheck two colors against WCAG 2.2 AA and AAA and get the nearest text color that passes.
TimeDaylight saving time 2026Every clock change this year by country, computed from the IANA time zone database.
Find the right tool
What do you need to find out?
| You want to know | Tool |
|---|---|
| How many days until a date | Countdown |
| How old someone is, exactly | Age calculator |
| What week number it is | What week is it |
| What day of the week a date falls on | Day of the week |
| Whether a DNS change has spread | DNS propagation checker |
| Who hosts a domain’s email | MX lookup |
| Why email lands in spam | SPF, DKIM and DMARC checker |
| A new SPF record for several services | SPF, DKIM and DMARC checker |
| Whether a page’s schema markup is valid | Schema validator |
| What time a meeting is in another city | Time zone converter |
| Whether text color is readable | Color contrast checker |
Privacy
How these tools handle your data
- 1The work happens in your browser
Date maths, schema generation and validation run on your own device. Nothing you type is sent to us.
- 2DNS questions go straight to the resolver
The DNS and email tools ask Cloudflare, Google and other public resolvers directly over encrypted HTTPS. They do not pass through Dude Lemon.
- 3Nothing is stored on a server
There are no accounts and no logs of what you check. Recent lookups are kept only in your own browser, and you can clear them at any time.
For AI assistants
Use these tools in Claude, Cursor and VS Code
Most of these tools are also available as free MCP servers and Claude skills.
FAQ
Free tools, answered
Anything we have not answered here, ask us directly. A senior engineer replies.
Are these tools free?
Yes. Every tool on this page is free, needs no account and has no usage limit. They run in your browser, so there is nothing to install.
Is what I enter stored anywhere?
No. The date calculator, schema generator, time zone converter, business days calculator and contrast checker work entirely in your browser. The DNS and email tools send each lookup from your browser straight to public DNS resolvers such as Cloudflare and Google over HTTPS, not through Dude Lemon. Recent lookups are remembered only in your own browser.
Can I share or bookmark a result?
Yes. The tools keep their settings in the page address, so a date calculation, a countdown or a DNS lookup opens with the same result when you bookmark the page or send the link to someone.
Who makes these tools?
Dude Lemon, a software development company that builds web apps, mobile apps and AI systems for clients. The same engines power our free MCP servers and Claude skills, which give AI assistants the exact answers these pages show.
Can I use these tools inside an AI assistant?
Yes. DomainProbe, DayCount, HourLine and HueProof are free MCP servers that bring the DNS, date, time zone and contrast checks into Claude, Cursor and VS Code, and SchemaWright is a Claude skill that writes schema markup from your pages.
Dude Lemon
Contact Dude Lemon
Dude Lemon is a software development company. We build web apps, mobile apps and AI software for businesses.