Free web tools for developers
App-Kit builds proprietary web tools and backend infrastructure. Compress an image or run a 400+ point SEO audit in seconds — free on the site, or via API by credits. No sign-up needed to start.
Free tools for developers
Small, fast utilities for everyday work on websites. Free, no sign-up — new image tools ship regularly.
Image Compressor
Compress JPG & PNG into WebP or AVIF.
free · no sign-upImage Resizer
Resize and crop: 1:1, 16:9, 4:3 presets.
free · no sign-upSEO Audit
400+ checks, score and fix list for any page.
freeText Analyzer
Readability, keyword stuffing, filler and grammar — up to 20,000 characters.
free · no sign-upPDF to Image
PDF pages as JPG, PNG or WebP — one by one or as a ZIP.
free · no sign-upWebP / AVIF converter
JPG and PNG into modern web formats, in batches.
free · via APIFour steps to the result
- 01
Pick a tool
Choose from the tools page or the menu.
- 02
Drop your file
Drag it in — or paste a URL for the audit.
- 03
Processing
Files are processed in seconds.
- 04
Download
Grab the result, one file or a whole zip.
Common jobs, solved fast
Convert images to WebP or AVIF
Batch conversion via the App-Kit API — smaller files, faster pages.
Shrink photos for your site
WebP/AVIF at the quality you pick — pages load faster.
Audit before launch
Catch missing meta, alt and indexing issues in a minute.
Pick the right format
Which format to use where — with real numbers.
Fix an unopenable AVIF
iPhone photo won't open? Three ways to convert.
Run the full SEO checklist
The 18 checks we run on every project.
Guides & case studies
State of SEO on the Russian web 2026: a study of 901 sites
An App-Kit study of 901 sites in the .ru and .рф zones from the Tranco top 1M, up to 10 pages each. 58% have no canonical tag, 69% no JSON-LD, 79% no CSP, and only 8% publish an llms.txt.
Vitaliy SazonovAI SEO audit: how to make your site visible to ChatGPT, Perplexity and AI Overviews
We checked robots.txt and llms.txt on 25 SaaS sites and 21 large Russian sites. 17 of 25 SaaS sites ship an llms.txt, only 3 Russian sites do, and 5 more return an HTML page with a 200 status instead of the file.
Vitaliy SazonovHow to Convert a PDF to JPG, PNG or WebP (and Which Resolution to Pick)
Every PDF page can become its own image. We ran three documents through our converter at 96, 150 and 300 dpi and compared JPG, PNG and WebP: JPG came out 8.5 times heavier than PNG for a diagram, and WebP was 10 times lighter for a scan.
Vitaliy SazonovOnline Text Checker: Readability, Keyword Stuffing, Filler and Grammar
Seven scores that tell you a draft needs another pass: readability, keyword stuffing, filler share, keyword density, top words, clichés and grammar. Targets, formulas and one paragraph measured before and after an edit.
Vitaliy SazonovFree Online SEO Audit: 400-Point Website Check with a Score and PDF
An online audit runs your site through 400 checks in 36 groups and returns a 0–100 score with priorities. We audited our own site, scored 70.5, and break down every finding.
Vitaliy SazonovHow to Resize an Image Online: The Complete Guide
Resizing to the width you actually need cuts up to 86% of file weight. When to resize, when to crop, when to compress — with honest measurements of one real photo.
Vitaliy SazonovWebP vs JPG vs PNG: which image format to use in 2026
One image, four formats, a real test with our converter: WebP is 45–50% lighter than JPG, PNG is 5× heavier. Here is when each format wins.
Vitaliy SazonovHow to convert AVIF to JPG (3 ways)
Saved an image from a site and got an .avif your editor won't open? Three ways to get a JPG — with real timings and the transparency catch.
Dmitry ChernenkoTechnical SEO audit checklist: 18 checks that actually matter
18 checks from our SEO audit canon in six groups — with IDs, priorities and fixes. Plus a real case: our own site went from 70.5 to 93.
Vitaliy SazonovBuilt by a small engineering team
App-Kit is an independent team. We ship the tools we need ourselves, and each of us keeps building under our own name.
Vitaliy Sazonov
Lead Engineer / CTO
Dmitry Chernenko
Senior Full-Stack
Alexander Naumenko
Senior iOS
Yulia Sazonova
Designer
Free on the site. Automate with the API.
Use the tools free on the web — for scripts and bulk work the same engine is available via API, paid by credits. In Claude and Cursor, the SEO audit, text checks and PDF tools run through the MCP server.