The Complete Guide to Free Online Tools: Calculators, Converters & SEO Tools

SEO Stack Tools Editorial Team

07/16/2026 4:00 PM

7 min read

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SEO Stack Tools offers 380+ free online tools spanning SEO auditing, calculators, unit converters, developer utilities, image editing, SSL/security, and social media downloads. This page is the master directory — every in-depth guide on this blog, organized by category, so you can find the right tool and the full tutorial behind it in one place.

SEO & Website Audit Tools

Tools for tracking rankings, auditing technical SEO, and analyzing backlinks.

Keyword Position Checker — track your Google rankings
Keyword Density Checker — optimize content for SEO
Keyword Suggestion Tool — find high-traffic keywords
Long Tail Keyword Finder — target low-competition terms
Backlink Checker — analyze your link profile
Backlink Maker — build quality backlinks for free
Domain Authority Checker — measure site authority
Page Authority Checker — measure a page's SEO power
Meta Tag Generator — create SEO meta tags instantly
Meta Tags Analyzer — check any page's meta data
Website SEO Score Checker — audit your site for free
Code to Text Ratio Checker — improve your SEO score
Broken Links Finder — detect & fix dead links
Redirect Checker — test 301, 302 & HTTP redirects
Robots.txt Generator — create & test your robots file
XML Sitemap Generator — create sitemaps for SEO
Google Index Checker — is your page indexed?
Google Cache Checker — view Google's cached page
Mobile Friendly Test — is your website mobile-ready?
Page Speed Checker — test & improve load time
PageSpeed Insights Checker — measure Core Web Vitals
GZIP Compression Checker — test if your site uses GZIP
Htaccess Redirect Generator — create .htaccess rules
Disavow File Generator — disavow toxic backlinks
Link Analyzer — audit all links on a page
Link Price Calculator — estimate the value of a link
Website Worth Calculator — estimate your site's value
Domain Age Checker — how old is a domain?
Domain Hosting Checker — find who hosts a website
Whois Lookup — find domain owner & registration info
Blacklist Lookup — is your domain blacklisted?
Class C IP Checker — detect shared IP hosting risks
Response Time Checker — test your website's speed
Server Status Checker — check if a website is down
Online Ping Website Tool — check if any site is up
Page Size Checker — check a page's file size
IP Address Lookup — find location & owner of an IP
Find DNS Records — look up DNS of any domain

Calculators

Financial, fitness, and general-purpose calculators.

Loan Calculator — monthly payments & total interest
Discount Calculator — percentage off & stacked discounts
Sales Tax Calculator — add or extract tax from any price
Calorie Calculator — find your daily calorie needs
TDEE Calculator — total daily energy expenditure
PayPal Fee Calculator — calculate transaction fees
AdSense Calculator — estimate your Google AdSense income
Age Calculator — calculate exact age from date of birth
Binary Calculator — add, subtract binary numbers

Unit & Format Converters

Convert between measurement units, number bases, and data formats.

Length Converter — metric & imperial units explained
Weight Converter — kilograms, pounds & stone
Temperature Converter — Celsius, Fahrenheit & Kelvin
Decimal to Binary Converter
Binary to Decimal Converter
Decimal to Hex Converter
Hex to Decimal Converter
HEX to RGB Converter
RGB to HEX Converter
Text to Binary Converter
Binary to Text Converter
JPG to PNG Converter
PNG to JPG Converter
CSV to JSON Converter
JSON to CSV Converter
Base64 Encoder
Base64 Decoder
URL Encoder
URL Decoder
HTML to Text Converter
Convert Image to Base64

Content & Writing Tools

Check, rewrite, and format written content.

Plagiarism Checker — detect duplicate content
Article Rewriter Tool — rewrite content without plagiarism
Paraphrasing Tool — rewrite text & avoid plagiarism
Grammar Checker — fix grammar errors instantly
Grammar Check — proofread & correct your writing
Spell Checker — find & fix spelling errors
Word Counter — accurate word counts
Character Counter — count characters & words
Sentence Counter — count sentences in any text
Online Text Editor — write & format text in browser
Text to Speech — convert any text to audio
Lorem Ipsum Generator — create placeholder text
Change Text Case — UPPER, lower & Title Case
Reverse Text Generator — flip & mirror text
Remove Duplicate Lines — clean up text lists
Remove Extra Spaces — clean whitespace from text

Image Tools

Compress, resize, crop, and analyze images.

Compress JPEG — reduce JPEG file size
Compress PNG — shrink PNG files without losing quality
Image Optimizer — compress images without quality loss
Crop Image Online — trim & resize images
Resize Image — change image dimensions
Reverse Image Search — find where an image appears
Image to Text (OCR) — extract text from images
Website Screenshot Generator — capture any web page

Developer Tools

Code formatting, minification, and generation utilities.

JSON Formatter — format & validate JSON
CSS Beautifier — format & prettify CSS code
CSS Minifier — compress CSS files
JavaScript Beautifier — format JS code
JavaScript Minifier — compress JS files instantly
HTML Beautifier — format & prettify HTML
HTML Minifier — compress HTML to speed up sites
UUID Generator — create unique IDs
Password Generator — create strong secure passwords
Password Strength Checker — is your password secure?
Color Picker — find & copy HEX, RGB color codes

SSL Certificates & Security

Generate, decode, and verify SSL certificates and CSRs.

SSL Checker — verify your SSL certificate is valid
SSL Certificate Checker — verify your SSL online
SSL Converter — convert certificates between formats
SSL Certificate Converter — convert PEM, DER, PFX
Certificate Decoder — read SSL certificate details
Certificate Decoder (detailed)
CSR Generator — create certificate signing requests
CSR Generator (detailed)
CSR Checker — verify & decode your CSR
CSR Decoder — decode & verify CSR files
SSL Key Mismatch Checker — does your certificate match your key?

YouTube & Video Tools

Optimize and manage YouTube content.

YouTube Tag Generator — find the best tags for videos
YouTube Tags Extractor — spy on any video's SEO tags
YouTube Title Generator — write titles that get clicks
YouTube Description Generator — write better descriptions
YouTube Channel Logo Downloader — save channel icons
YouTube Thumbnail Downloader — save HD thumbnails

Social Media Downloaders

Save videos from major social platforms.

Social Media Downloader — save videos from any platform
Facebook Video Downloader
TikTok Video Downloader — no watermark
Twitter Video Downloader
SoundCloud Downloader — save songs as MP3
YouTube Video Downloader — for offline viewing

General SEO Guides & Strategy

Broader strategy guides not tied to a single tool.

Why Use Free Online Tools Instead of Desktop Software?

Every tool on this site runs directly in your browser — no installation, no signup, no per-tool subscription. For occasional tasks (converting a file format, checking a domain's SSL status, formatting a chunk of JSON), installing dedicated desktop software is overkill. Browser-based tools also mean you can use them from any device, including phones and tablets, without worrying about OS compatibility.

Frequently Asked Questions

Are all these tools really free?

Yes — every tool linked on this page is free to use with no signup required. Some tools have reasonable usage limits to prevent abuse, but there's no paywall for core functionality.

How do I find the right tool for my task?

Use the category sections above to browse by task type, or use the search bar at the top of any page to search all 380+ tools directly by name.

Is my data safe when I use these tools?

Many tools (text formatters, converters, calculators) run entirely client-side in your browser — your data never leaves your device. Tools that require server processing (like domain lookups) only send the specific data needed for that lookup, never stored beyond what's needed to return your result.