Free online developer tools — browser-based, no upload
Format, validate, and debug in the browser — no signup, no server processing of your payloads. Start from a language hub below or open a specific tool. Structured data on every indexable page.
Hubs by format
All developer tools
AI Token Counter (GPT, Claude, Gemini)
Count tokens with o200k-style tokenization, then compare estimated LLM API cost across 30+ models. Pairs with the per-token cost calculator; all in-browser.
Open tool →API rate limit checker
TPM and RPM headroom against illustrative dev/production tiers.
Open tool →Audio API cost estimator
Duration-based illustrative cost bands for speech and TTS-style workloads.
Open tool →Base64 encode / decode
Standard and URL-safe Base64; text and small file drops — client-side only.
Open tool →Context window visualizer
Prompt + history size vs model context with 70% / 90% markers.
Open tool →Cron Expression Builder & Generator
Free online cron builder: translate schedules to plain English, validate syntax, and preview next runs.
Open tool →Diff Checker
Online diff checker tool — compare CSV, XML exports, or text side-by-side with line-level highlighting.
Open tool →Discord Timestamp Converter
Generate Discord dynamic t: timestamps from Unix epoch — copy default, full, relative, time, or date styles.
Open tool →Embedding cost calculator
Float32 GB estimate plus embedding API math for ingest and monthly queries.
Open tool →Fine-tune vs prompt calculator
Break-even requests after a one-time fine-tune fee using your $/M assumptions.
Open tool →HTML Converter
Convert HTML entities or transform HTML to JSX/Markdown.
Open tool →HTML Formatter
Beautify HTML code with proper indentation.
Open tool →HTML Minifier
Compress HTML by removing whitespace and comments.
Open tool →HTML Validator
Check HTML for syntax errors and standard compliance.
Open tool →JS Converter
Convert between JavaScript versions or transform to/from TypeScript.
Open tool →JS Formatter
Beautify and format JavaScript code with proper indentation.
Open tool →JS Minifier
Compress JavaScript code by removing whitespace and unnecessary characters.
Open tool →JS Validator
Check JavaScript code for syntax errors and quality issues.
Open tool →JSON Converter
Convert JSON data to XML, YAML, CSV, or HTML formats.
Open tool →JSON Formatter
Pretty-print JSON, mask likely secrets, and copy bash cURL or Postman import — for webhooks and API payloads.
Open tool →JSON Validator
Validate JSON syntax and structure against schemas.
Open tool →JWT Debugger
Decode, inspect, and verify JSON Web Tokens with HMAC signature checking.
Open tool →LLM API cost (per token count)
Enter input and output token counts; compare price across 30+ models. Deep-links from the token counter; cache- and reasoning-aware.
Open tool →LLM model comparison (2–4 models)
Side-by-side matrix: context, API $/M, capabilities; shareable ?models= links. Pairs with token counter and cost calculator.
Open tool →LLM pricing changelog
Editorial log of llm-pricing.json updates; pairs with /feed/pricing.xml.
Open tool →LLM scenario planner
Users × requests/day × tokens with ×2/×5 stress and 12‑month projection for one reference model.
Open tool →Markdown to HTML
MD → HTML with email-safe mode, optional changelog wrap, scripts stripped in-browser.
Open tool →Number to Words Converter
Number to words online, A1Z26 letter–number cipher, and phone keypad vanity mapping — all in your browser.
Open tool →Password Generator
Generate strong, random passwords and passphrases with a live entropy score.
Open tool →Prompt caching calculator
Compare per-request cost with and without prompt cache hits using published cached-input rates.
Open tool →QR code generator
Create QR codes for URLs, text, Wi‑Fi, and vCard — PNG download, error correction, colors.
Open tool →RAG cost simulator
Documents × chunks × top‑K × daily queries × output tokens — illustrative monthly LLM spend.
Open tool →Regex Tester
Regex tester online with Go RE2, bash/grep, sed -E, Perl, and C# flavor guides — live matches in your browser.
Open tool →Timestamp Converter
Convert between Unix epoch timestamps and human-readable dates across time zones.
Open tool →UUID / ULID / NanoID Generator
Generate secure UUID v4, ULID, and NanoID identifiers in bulk.
Open tool →Vision token estimator
Rough planning estimate for image width/height → vision tokens.
Open tool →XML Converter
Convert XML data to JSON, YAML, or CSV formats.
Open tool →XML Formatter
Beautify and format your XML code for readability.
Open tool →XML Minifier
Compress XML by removing unnecessary whitespace.
Open tool →XML Validator
Check XML for well-formedness errors.
Open tool →