Developer Tools
44 free tools in this category · No signup · Open source
JSON Formatter
Format, validate, and minify JSON instantly. Sort keys alphabetically, view error posi…
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URL Encoder / Decoder
Encode or decode URLs and query strings. Supports component encoding, full URL encodin…
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UUID Generator
Generate RFC 4122 v4 UUIDs. Bulk generate up to 1000 at once, choose uppercase, no-hyp…
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JWT Decoder
Decode and inspect JSON Web Tokens. View header, payload, expiration, issuer, and veri…
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Regex Tester
Test JavaScript regular expressions with live match highlighting, capture groups, repl…
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Timestamp Converter
Convert between Unix timestamps, ISO 8601, and human-readable dates. Supports millisec…
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SQL Formatter
Format and beautify SQL queries instantly. Supports PostgreSQL, MySQL, SQLite, BigQuer…
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Cron Expression Builder
Build, validate, and explain cron expressions in plain English. Preview the next 5 run…
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YAML Formatter & Validator
Format and validate YAML — for Kubernetes manifests, Docker Compose, GitHub Actions, A…
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XML Formatter
Pretty-print XML with proper indentation. Handles SOAP responses, RSS feeds, configura…
IP CIDR Calculator
Calculate network details from CIDR notation: netmask, broadcast, first/last host, tot…
.gitignore Generator
Generate a properly-curated .gitignore file by selecting your language, framework, OS,…
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HTTP Headers Inspector
Inspect HTTP response headers from any URL. See server, content-type, caching, and aud…
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JSON to TypeScript Interface
Convert any JSON document into TypeScript interfaces. Smart array merging produces opt…
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JSON Diff
Compare two JSON documents and see exactly what changed. Semantic diff — object key or…
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curl → fetch / axios / Python / Go
Paste a curl command, get the equivalent code in JavaScript fetch, axios, Python reque…
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JS / CSS / HTML Beautifier + Minifier
Beautify minified or messy JavaScript, JSX, JSON, CSS, SCSS, or HTML. Optional JavaScr…
Unix Timestamp Converter
Convert between Unix timestamps (seconds, milliseconds, microseconds, nanoseconds) and…
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HTTP Status Code Reference
Every HTTP status code (60+) with plain-language explanation, typical use cases, and b…
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User-Agent Parser
Parse any User-Agent string into browser name and version, OS, device type, engine, an…
IPv4 Address Converter
Convert an IPv4 address between dotted decimal, integer (32-bit), hex, octal, binary, …
JSON Schema Generator
Generate a JSON Schema (Draft 07 or 2020-12) from any JSON document. Auto-detects form…
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JSON Schema Validator
Validate a JSON document against a JSON Schema (Draft 07 and 2020-12). Powered by Ajv …
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JSONPath Tester
Evaluate JSONPath expressions (RFC 9535 / Goessner) against a JSON document. Test filt…
Color Contrast Checker (WCAG + APCA)
Check color contrast against WCAG 2.1 AA/AAA thresholds and the modern APCA (WCAG 3 dr…
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Subnet Mask Calculator (CIDR)
Convert CIDR notation to subnet mask, wildcard mask, network range, broadcast address,…
Favicon Generator (all sizes + manifest)
Upload one square image, get a complete favicon package: 16/32/48/180/192/512 PNGs, Ap…
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Open-Source License Picker
Answer 4 questions and get the right open-source license for your project — MIT, Apach…
README.md Template Generator
Generate a polished README.md tailored to your stack (Node, Python, Go, Rust, Ruby, PH…
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Cron Expression Explainer + Visualizer
Paste a cron expression — get a plain-English description, field-by-field breakdown, a…
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URL Parser & Builder
Break a URL into its components (protocol, host, port, path, query, fragment), edit th…
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DNS Record Lookup
Look up A, AAAA, MX, TXT, NS, CNAME, SOA, CAA, SRV, and PTR records for any domain. Li…
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SPF / DKIM / DMARC Checker
Inspect a domain's email authentication setup: SPF policy, DKIM public keys, DMARC pol…
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Email Header Analyzer
Paste raw email headers; get the full delivery path (Received chain with per-hop timin…
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JSON ↔ CSV Converter
Bidirectional converter between JSON arrays and CSV. Handles nested objects (flattens …
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SSL/TLS Certificate Inspector
Paste a PEM-encoded certificate; see issuer, validity period with expiry countdown, Su…
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Mermaid Diagram Renderer
Render Mermaid diagrams instantly — flowcharts, sequence, class, state, ER, Gantt, pie…
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YAML ↔ JSON Converter
Bidirectional converter between YAML and JSON with proper handling of anchors, aliases…
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Base Converter (Any Radix)
Convert numbers between any base from 2 to 62. Binary, octal, decimal, hex, base 32, b…
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HTTP Headers Inspector
Fetch any URL's HTTP response headers and audit them for security best practices. Show…
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Markdown ↔ HTML Converter
Bidirectional converter between Markdown and HTML. GitHub Flavored Markdown features: …
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Timezone Converter
Pick a date/time in one zone, see it in every zone you care about. Add/remove zones to…
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Conventional Commits Builder
Build properly-formatted Conventional Commits messages. Type/scope/subject/body/footer…
HTTP Cookie Parser
Parse Set-Cookie or Cookie headers into readable tables. Shows all attributes (Path, D…