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Guides for the tools on this site — and the problems that send people looking for them.
JSONJSON Formatter: The Complete Guide to Format, Validate & Debug JSONThe complete JSON formatter guide — syntax rules, real parser errors, security risks, and precision bugs. Free, client-side JSON formatter, no sign-up.DatabaseUUID Generator: The Complete Guide to UUID v4, v7 & GUIDsFree UUID generator for UUID v4 and v7 — client-side, no sign-up. Covers UUID vs GUID, collision odds, and code for Python, JS and SQL.RegexRegex Tester: Test and Debug JavaScript Regular Expressions OnlineFree regex tester for JavaScript patterns — live match highlighting, named groups, replace preview. No sign-up, runs in your browser.APIcURL to Python: Convert Any cURL Command to requests CodeConvert curl to Python requests code free — headers, JSON bodies, multipart uploads, Basic Auth and cookies mapped correctly. No sign-up.SQLSQL Formatter: Beautify SQL for Postgres, MySQL and SQL ServerFree SQL formatter for PostgreSQL, MySQL and SQL Server — clauses on their own lines, dialects explained, no sign-up, no ads.JSONIs My JSON Valid? How to Tell Syntax Errors from Schema MismatchesCheck if JSON is valid free online — tells syntax errors from schema mismatches, with fixes for common JSON errors. No sign-up.JSONCSV to JSON: Convert Spreadsheet Data to JSON OnlineConvert CSV to JSON free online — array, nested, or JSON Lines output, RFC 4180 quoting, no upload required.JSONJSON Diff: Compare Two JSON Files and Spot Every Real ChangeJSON diff tool, free online — compare two files structurally, ignoring key order and whitespace, with JSON Patch export.JSONJSON Schema Validator: Validate JSON Against Draft 2020-12Free JSON Schema Validator (draft 2020-12) online — validate JSON structure with errors located by JSON Pointer. No sign-up.JSONJSON Minifier: Compress JSON and See the Exact Byte SavingsFree JSON minifier — strip whitespace and see exact byte savings. Parses first, so invalid JSON is located, not mangled.JSONJSON to TypeScript: Generate Interfaces from Any JSON SampleFree JSON to TypeScript converter — generates interfaces from samples, merging fields into optional props and unions.JSONJSONPath Tester: Query and Extract Data from JSON InstantlyTest JSONPath expressions against real JSON and see every matching node with its normalized path. Free JSONPath evaluator with wildcards and filters — runs entirely client-side.JSONJSON to Zod: Generate a Zod Schema From a JSON SampleGenerate a Zod schema from JSON online — optional fields and unions inferred correctly from multiple samples, Zod 4 and Zod 3 output. Free, client-side, no sign-up.JSONJSON Parse Error: Unexpected Token — Every Cause, ExplainedFix "JSON parse error: unexpected token" fast — the real causes (trailing commas, single quotes, unquoted keys) with exact error text and fixes. Free JSON formatter, no sign-up.DatabaseUUID v4 Generator: Generate RFC 4122 Random UUIDs OnlineFree UUID v4 generator — cryptographically random, RFC 4122 compliant. See the version/variant bits, the real collision math, and why crypto.getRandomValues matters.DatabaseULID vs UUID: Which Should You Use for Sortable IDs?ULID vs UUID for primary keys — ULIDs are lexicographically sortable and monotonic, so inserts stay index-friendly. Free client-side ULID generator included.DatabaseHow to Generate Test Data for a Database (Without Copying Production)How to generate test data you can commit: reproducible seed rows, safe values that cannot reach a real person, and SQL inserts for Postgres or MySQL.SecurityJWT Decode vs Verify: Why They're Not the Same ThingJWT decode vs verify — decoding reads the payload, verifying proves the signature is real. Free JWT decoder with HS256/384/512 verification, entirely client-side.SecurityJWT Generator: Create and Sign a JWT Token Online with Custom ClaimsFree JWT generator — sign tokens with HS256/384/512 and custom claims, generate a throwaway secret, and test expired or malformed tokens safely.SecurityBase64 Encode & Decode: Convert Text, Images, and Files OnlineFree Base64 encoder/decoder with full Unicode support — standard vs. URL-safe variants explained, plus file-to-data-URI conversion. Runs entirely client-side.SecurityHash Generator: MD5, SHA-1, SHA-256 and SHA-512 Checksums OnlineFree hash generator — SHA-1/256/384/512, MD5 and HMAC digests computed locally with WebCrypto. Verify file integrity and understand hash vs. HMAC.APICurl to Code: Convert Any curl Command to Python, JavaScript or NodeConvert curl commands to fetch, Axios, Node https or Python requests code free online — headers, body and auth mapped correctly. No sign-up, nothing uploaded.APIGraphQL Formatter: Beautify and Minify Queries, Mutations and SchemasFree GraphQL formatter — beautify or minify queries, mutations, fragments and SDL schemas with a real parser. Syntax errors located by line and column.APIHAR File Analyzer: Inspect Network Requests Without Uploading ThemFree HAR file analyzer — read the network waterfall and timing breakdown client-side, with a one-click redacted copy since HAR files leak cookies and tokens.SQLParameterized Query Builder: Build Safe SQL for Postgres, MySQL and SQL ServerFree parameterized query builder for Postgres, MySQL and SQL Server — every query built with placeholders, never string concatenation, with a warning when a query is valid but not what you meant.SQLEXPLAIN ANALYZE in Postgres: How to Read the OutputHow to read Postgres EXPLAIN ANALYZE output — Seq Scan vs Index Scan, join algorithms, estimated vs actual rows, and the LEFT JOIN bug a WHERE clause can hide.SQLSQL Minifier: Shrink Query Size Before Sending It to ProductionFree SQL minifier — collapses queries to one line and strips comments without touching string literals or quoted identifiers. Parses before minifying.RegexGlob Pattern Tester: Validate Wildcards and .gitignore RulesFree glob and .gitignore pattern tester — see exactly which rule matched each path, including which negation won. No sign-up, runs in your browser.RegexRegex Generator: Turn Plain-English Descriptions or Examples Into a PatternFree regex generator — build from labeled blocks or infer from matching and non-matching examples, verified against both sets before you trust it.OpenAPIOpenAPI Validator: Validate Your Spec Online for FreeFree OpenAPI validator for 3.0 and 3.1 — every structural error located by JSON Pointer, unresolved $ref references reported rather than skipped.OpenAPIOpenAPI Diff: Compare Two Specs and Catch Breaking ChangesFree OpenAPI diff tool — compare two spec versions and see exactly which changes are breaking vs. safe, with the reason for each. Runs client-side.OpenAPIOpenAPI YAML to JSON Converter (and Back)Free OpenAPI YAML to JSON converter — convert either direction and sort keys into specification order for clean, minimal version-control diffs.UtilitiesUnix Time Explained: Epochs, Milliseconds and the 2038 ProblemWhat a Unix timestamp actually is, why the same number can mean seconds or nanoseconds, how timezones fit in, and what breaks on 19 January 2038.UtilitiesDiff Checker Online: Compare Text and Spot Every Real ChangeFree online diff checker — line and word-level highlighting, whitespace/case-insensitive options, and a unified diff you can save as a patch.UtilitiesURL Encoder / Decoder: Encode or Decode Any String OnlineFree URL encoder/decoder with explicit component, full-URL and form modes — because encodeURIComponent and encodeURI aren't interchangeable.AIToken Counter: Count Tokens for GPT, Claude & Any LLM FreeFree token counter with a real BPE tokenizer, in your browser — count tokens exactly for GPT, Claude and Llama, then see the cost before you send it.AILLM Pricing Calculator: Compare GPT and Claude API CostsFree LLM pricing calculator — model a real workload (requests/day, tokens in/out) across GPT and Claude, including the prompt-cache hit rate that decides the bill.AIHow to Shorten a Prompt Without Losing QualityCut prompt tokens without changing what the prompt asks for: which edits are safe, which quietly change the output, and how to price the saving.AIOpenAI Strict JSON Schema: What Structured Outputs Actually AcceptsOpenAI strict JSON Schema explained — which keywords structured outputs and function calling actually accept, checked before you hit a 400. Free, client-side.DevOpsYAML to JSON: Convert Config Files to JSON InstantlyFree YAML to JSON converter — bidirectional, with exact line/column errors for indentation mistakes instead of a stack trace. Covers the Norway problem.DevOpsCron Expression Generator: Build Cron Schedules Without GuessworkFree cron expression generator and explainer — see the next run times in plain English, and avoid the day-of-month/day-of-week OR-not-AND mistake.SecuritySecure Random Password Generator for Developers and API KeysA secure random password generator built for developers — entropy explained, why Math.random() is unsafe for secrets, and a free client-side tool.DevOps.env File Syntax Explained: The Complete Dotenv Format GuideThe complete .env file syntax guide — quoting rules, multiline values, comments, and variable expansion, with a free client-side .env parser and validator.DevOpsDotenv Best Practices: Fixing "Environment Variables Not Loading"Dotenv best practices for fixing environment variables not loading — load order, .env.local precedence, and the mistakes that silently break config.SecurityHow to Read an SSL Certificate: Every Field ExplainedWhat each field in an X.509 certificate means — subject, issuer, SANs, key usage, basic constraints — and which ones actually decide whether a connection works.SecurityHow to Check SSL Certificate Expiration (OpenSSL or Online)Check when an SSL certificate expires: the OpenSSL one-liner for a live host, your browser's padlock, or paste the certificate to read its expiry date and days remaining.DatabasePrisma vs Drizzle: Which TypeScript ORM Should You Use in 2026?Prisma vs Drizzle compared — schema philosophy, generated types, migrations, and runtime overhead, so you can pick the right TypeScript ORM in 2026.DatabasePrisma Formatter: Clean Up and Format Your schema.prisma FileFormat and clean up a messy schema.prisma file online — consistent field alignment and indentation, no CLI install required.DevOpsDocker Compose vs Kubernetes: Which Should You Use for Local Development?Docker Compose vs Kubernetes for local development — complexity, orchestration features, and when a Compose file is genuinely enough.DevOpsKubernetes Deployment YAML Example: Copy-Paste TemplatesCopy-paste Kubernetes Deployment YAML examples — Deployment, Service, and env-var patterns, validated before you apply them.OpenAPIOpenAPI SDK Generator: Generate API Clients From Your Spec OnlineGenerate a typed API client straight from your OpenAPI spec — no dependencies, and it flags exactly what your spec left too vague to type.APIWhat Is a CSP Header? Content Security Policy ExplainedWhat a Content-Security-Policy header actually does, how directives work, and how to read one without guessing what each source list means.OpenAPIOpenAPI Mock Server: Mock APIs From Your Spec InstantlyTurn an OpenAPI spec into a working mock API instantly — realistic example responses for every endpoint, no backend required.RegexRegex Cheat Sheet PDF: Download a Printable Quick ReferenceA printable regex cheat sheet covering anchors, character classes, quantifiers and lookaheads — quick reference, free to use online or print.DatabaseMongoDB vs PostgreSQL: Which Database Should You Choose?MongoDB vs PostgreSQL compared — schema flexibility, joins vs embedding, consistency guarantees, and which fits your data model best.DatabaseHow to Write a MongoDB Query: A Beginner's GuideHow to write a MongoDB query step by step — find filters, operators like $gt and $in, and building queries visually instead of guessing syntax.APICurl to PowerShell: Convert curl Commands to Invoke-RestMethodConvert a curl command to PowerShell's Invoke-RestMethod — headers, JSON bodies, and the gotchas curl.exe vs the PowerShell alias causes.UtilitiesMarkdown Preview Online: Write and Render Markdown in Real TimeWrite Markdown and see it rendered in real time, right in your browser — free live Markdown preview, no sign-up, nothing uploaded.UtilitiesQR Code Generator: Create Custom QR Codes Online for FreeGenerate a custom QR code online for free — URLs, text, or Wi-Fi credentials, with adjustable size and error correction. No sign-up.JSONJSON Skills Roadmap: From Beginner to API Data ModelingA staged JSON skills roadmap — from reading and formatting JSON to schema validation, TypeScript types, and real API data modeling.DatabaseDatabase Identifiers Roadmap: UUIDs, ULIDs, and Choosing the Right ORMA staged roadmap for database identifiers — UUIDs vs ULIDs vs auto-increment, then choosing and formatting the right ORM for your schema.SecurityWeb Security Roadmap: JWT, Hashing, and Certificates Explained Step by StepA staged roadmap for web auth and encoding — JWTs, password hashing, Base64 vs encryption, and SSL certificates, explained in the right order.APIAPI Development Roadmap: From curl to Full API Testing WorkflowsA staged API development roadmap — from your first curl request to headers, CORS, OpenAPI specs, and full API testing workflows.SQLSQL Roadmap: From Basic Queries to Query OptimizationA staged SQL roadmap — from basic SELECT queries and joins to indexes, execution plans, and query optimization.RegexRegex Roadmap: From Basic Patterns to Advanced LookaheadsA staged regex roadmap — from character classes and quantifiers to groups, lookaheads, and building real validation patterns.OpenAPIOpenAPI Roadmap: From Writing a Spec to Generating SDKs and MocksA staged OpenAPI roadmap — from writing your first spec to validating it, mocking it, and generating typed SDKs from it.UtilitiesEveryday Developer Utilities Roadmap: Encoding, Timestamps, and DiffingA staged roadmap for everyday developer utilities — URL/Base64 encoding, timestamps, text diffing, and the small tools that save real time.AILLM Development Roadmap: Tokens, Costs, and Prompt Engineering BasicsA staged LLM development roadmap — tokens and context windows, cost calculation, and prompt engineering fundamentals, in the right order.DevOpsConfig File Roadmap: YAML, .env, and Cron for New DevOps EngineersA staged config-file roadmap for new DevOps engineers — YAML syntax, .env files, and cron expressions, covered in the order you'll actually need them.JSONJSON vs XML: Why Modern APIs Moved to JSONJSON vs XML compared — verbosity, parsing cost, schema support, and the real reasons modern APIs moved away from XML.JSONJSON vs YAML: Which Format Should You Use for Config Files?JSON vs YAML for config files — readability, comments, whitespace sensitivity, and when each format is the better choice.JSONJSON Lint: The Free JSONLint Alternative That Never Uploads Your DataA free JSONLint alternative that runs entirely in your browser — same syntax-error precision, without sending your JSON to a server.APIPostman Alternatives: 5 Free API Clients ComparedThe best free Postman alternatives, compared honestly: Bruno, Insomnia, Thunder Client, HTTPie and curl — what each one gives up, and which fits your workflow.APIcurl vs wget: Which Command-Line Tool Should You Use?curl vs wget compared — API calls vs file downloads, flag differences, and when each command-line tool is actually the right one.APIGraphQL vs REST API: Key Differences ExplainedGraphQL vs REST API compared — over-fetching, caching cost, versioning philosophy, and when GraphQL is actually worth the added complexity.SecurityMD5 vs SHA256: Key Differences and Which to UseMD5 vs SHA256 compared — collision resistance, output size, and why MD5 is still fine for checksums but wrong for anything security-sensitive.SecurityJWT vs OAuth: Understanding the Difference (They're Not the Same Thing)JWT vs OAuth — a token format compared against an authorization protocol. Why they're not the same thing, and how they actually work together.RegexRegex vs Glob Patterns: When to Use EachRegex vs glob patterns — why .gitignore and build tools use glob, why regex is more powerful, and when to reach for each one.UtilitiesencodeURI vs encodeURIComponent: When to Use EachencodeURI vs encodeURIComponent explained — which reserved characters each one escapes, and why using the wrong one silently breaks query strings.JSONHow to Format JSON: A Step-by-Step Guide for DevelopersHow to format JSON step by step — DevTools, JSON.stringify(null, 2) explained, python -m json.tool, jq ., and what a good online formatter should do.APIHow to Fix a CORS Error (With Real Header Examples)How to fix a CORS error, step by step — why it's a server-side fix, the Access-Control-Allow-Origin header, and reading a real preflight response.APIHow to Send a POST Request with curl (With JSON Body Examples)How to send a POST request with curl — JSON bodies, form data, file uploads, and the Content-Type header curl doesn't set for you automatically.RegexBest Regex Tester Extensions for VS Code (Test Patterns Live)Testing regex in VS Code — the built-in Find/Replace regex support, project-wide regex search, and what a dedicated extension adds on top.RegexHow to Write a Regex for Email Validation (With Edge Cases)A regex for email validation that actually works in production — plus-addressing, subdomains, and why a confirmation email is the real check.SQLHow to Read a SQL Explain Plan (With Annotated Examples)How to read an EXPLAIN plan step by step — annotated Postgres EXPLAIN ANALYZE output, Seq Scan vs Index Scan, and the estimate-vs-actual check.OpenAPIHow to Generate a TypeScript Client From an OpenAPI SpecHow to generate a typed TypeScript client from an OpenAPI spec — the operationId gotcha, a worked example, and why to regenerate instead of hand-edit.DatabaseBest UUID Generator Extensions for VS CodeGenerating UUIDs in VS Code — what extensions add over native snippets, multi-cursor insertion, and when bulk generation needs a dedicated tool.JSONJSON Interview Questions and Answers (Including Data Engineering)JSON interview questions and answers — fundamentals, data engineering (JSONB, JSON Lines, flattening), JSON Schema, and common gotchas.SQLSQL Interview Questions and Answers (2026 Edition)SQL interview questions and answers — joins, aggregation, query optimization, window functions, and the questions that trip candidates up.SQLSQL Syntax Cheat Sheet: Joins, Clauses, and Common FunctionsA quick-reference SQL syntax cheat sheet — clause write order vs execution order, join types, aggregate/string/date functions, and CRUD skeletons.RegexRegex Pattern Library: Common Patterns Explained With ExamplesA regex pattern library with real examples — phone numbers, URLs, hex colors, slugs, strong passwords, and IPv4, each with matches and known limits.