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Development

13 Free Online Developer Tools

This is the catch-all category for the 13 utilities that do not belong to a format or a language — the ones you reach for while setting a project up or working out why something in production is behaving oddly. There are generators for the boilerplate nobody enjoys writing: .gitignore files assembled from your stack, a GitHub README from a form, QR codes and barcodes, Dockerfile snippets. There are calculators and parsers for the syntax that is easy to get wrong: cron expressions read back in plain English with their next run times, IPv4 subnets broken down from a CIDR block, epoch timestamps across timezones, .env files converted to and from JSON. And there are lookups that answer a question about the outside world: DNS records over DNS-over-HTTPS, IP geolocation, bulk email address validation, and a SQL schema diff that writes the ALTER statements for you.

All 13 Development tools

What you can do with these developer tools

Four loose groups, depending on whether you are creating something, decoding something, or asking about something.

  • Generate boilerplate — .gitignore from your languages and editors, a polished README.md, Dockerfile snippets, QR codes, and barcodes.
  • Decode tricky syntax — explain a cron expression and preview its next 10 runs, break a CIDR block into network, broadcast, and host range, convert epoch values across timezones.
  • Reshape config — parse a .env file into a table or JSON and build one back from JSON, or diff two SQL schemas and generate the ALTER statements to sync them.
  • Look things up — query A, AAAA, CNAME, MX, TXT, NS, and SOA records for a domain, or check the geolocation, ISP, and network behind an IP address.
  • Validate in bulk — check a whole list of email addresses for syntax, disposable domains, role accounts, duplicates, and likely typos.

Which of these use the network

Most tools on this site never make a request, and the honest exception list matters. DNS Lookup queries Cloudflare over DNS-over-HTTPS, so the domain you type is sent to a resolver — the same as any nslookup. IP Address Info calls a geolocation API for the address you enter. Email Validator checks syntax, disposable domains, and typos entirely locally, and only reaches the network if you opt into the MX record check. Everything else in this category — the generators, the cron parser, the subnet calculator, the .env formatter, the SQL schema diff — runs fully in your browser, and each tool states which category it is in on its own page.

Related categories

Frequently asked questions

6

No. All 13 are free to use with no sign-up, no API key, and no usage limits, and almost all of them keep working offline once the page has loaded.

DNS Lookup queries a DNS-over-HTTPS resolver, IP Address Info calls a geolocation API, and Email Validator contacts the network only if you enable its optional MX check. The generators, calculators, and formatters run entirely in your browser.

Yes. Cron Expression Generator reads any crontab line back in plain English and lists the next 10 run times in your timezone or UTC, and it supports both 5-field crontab and 6-field Quartz or Spring syntax with seconds.

Enter the address with a CIDR prefix or subnet mask in IPv4 Subnet Calculator. It returns the network and broadcast addresses, the usable host range and count, the wildcard mask, a binary breakdown, and an equal split into smaller subnets.

No — that would require sending mail. It validates syntax against RFC 5321 and 5322, flags disposable and role addresses, finds duplicates and likely domain typos, and can confirm the domain has MX records, which together catch most bad addresses in a list.

Yes. Select every language, framework, and editor that applies and the generator merges the templates into one deduplicated file, so a Node plus Python plus VS Code project produces a single clean .gitignore.