JSON Tips & Guides
Practical articles for developers working with JSON, YAML, and API data.
Unexpected Token < in JSON at Position 0: Fix HTML Responses in fetch()
Fix Unexpected token < in JSON at position 0 by proving whether fetch() returned HTML: 404 pages, login redirects, SPA fallbacks, dev proxies, WAF blocks, and wrong API URLs.
12 min readUnexpected Token u in JSON at Position 0: Fix JSON.parse(undefined)
Fix Unexpected token u in JSON at position 0 by finding the undefined value passed to JSON.parse(): missing props, localStorage mistakes, async state, no-return functions, env vars, and unsafe fallbacks.
10 min readUnterminated String in JSON: Causes and Fixes
Fix unterminated JSON strings by finding the open quote, escaped closing quote, raw newline, or truncated response that left the value incomplete.
12 min readBad Escaped Character in JSON: Causes, Examples, and Fixes
Fix "bad escaped character in JSON" errors from \x escapes, Windows paths, regex strings, malformed \u values, and double-encoded JSON.
12 min readUnexpected Non-Whitespace Character After JSON: Fixes
Why JSON.parse read one value and then failed on extra data, plus fixes for concatenated objects, NDJSON, logs, fetch responses, and framed streams.
12 min readJSON Pretty Print vs Format: Same Output, Different Workflows
Pretty print, format, and beautify mean the same JSON operation. Learn the practical differences around validation, repair, minify, key sorting, tree view, CLI tools, numeric precision, and safe formatting.
11 min readJSON Tree Viewer: Explore Nested JSON Without Getting Lost
Use a JSON tree viewer to inspect large API responses, collapse noisy branches, read object and array paths, handle invalid JSON, compare shapes, and keep sensitive payloads local.
10 min readYAML Formatter: Re-Indent and Validate
Format YAML without hiding config bugs: fix indentation, catch parser errors, handle anchors, comments, type coercion, sorting, and YAML-to-JSON output.
13 min readXML to JSON: Attributes, Arrays & Namespaces
Convert XML to JSON without losing shape: attributes, text nodes, repeated elements, namespaces, CDATA, entities, type coercion, and code examples.
13 min readJSON to XML: Convert Online, JavaScript, and Python Without Losing Shape
Convert JSON to XML with practical rules for root elements, attributes, #text, arrays, namespaces, invalid tag names, escaping, XSD order, null values, types, JavaScript, Python, and browser-local tools.
12 min readHow to Convert JSON to CSV Without Losing Columns or Types
Convert JSON to CSV and back with practical rules for headers, quoting, nested objects, type coercion, Excel imports, and browser-local conversion.
11 min readHow to Validate JSON: Syntax, Schema, CI Checks, and Real Error Messages
Validate JSON syntax with JSON.parse, Python json.loads, jq, or a browser-local validator, then use JSON Schema for required fields, types, formats, and API contract checks.
12 min readHow to Stringify JSON with JSON.stringify: Values, Replacer, Space, and Escaping
Learn how JSON.stringify works in real JavaScript code: request bodies, pretty-printing, replacer functions, toJSON, BigInt, Map, Set, circular references, and JSON string literals.
12 min readJSON vs YAML: When to Use Each for APIs, Config, and CI
JSON vs YAML explained with practical examples for APIs, app config, Kubernetes, CI pipelines, type inference, comments, anchors, conversion, parser safety, and browser-local validation.
12 min readHow to Decode a JWT Safely: Header, Payload, Claims, and Verification
Decode a JWT locally, read header and payload claims, handle Base64url and Unicode safely, and understand why decoding is not signature verification.
11 min readJSON Patch vs JSON Merge Patch: RFC 6902 vs RFC 7396 for API Partial Updates
Choose between JSON Patch and JSON Merge Patch with concrete API examples: null handling, arrays, JSON Pointer paths, test operations, ETags, validation, idempotency, and server-side safety checks.
12 min readHow to Convert CSV and XML to JSON Without Losing Shape
Convert CSV and XML to JSON with practical mapping rules for headers, types, attributes, repeated elements, namespaces, and browser-safe validation.
11 min readjq Tutorial: Practical Examples, Filters, and a Copy-Paste Cheat Sheet
Learn jq with copy-paste commands for pretty-printing JSON, extracting fields, filtering arrays, reshaping API responses, passing shell variables, validating files, and exporting CSV.
12 min readJSON to TypeScript Interfaces: Generate Types That Survive Real APIs
Generate TypeScript interfaces from JSON samples safely. Learn when to use an online converter, quicktype, OpenAPI, Zod, multiple samples, optional fields, nullable values, arrays, enums, dates, and runtime validation.
13 min readWhat Is JSON Schema? Validation & Examples
What JSON Schema is, how validation works, the core keywords, draft 2020-12 examples, Ajv/Python validation, and mistakes to avoid.
15 min readHow to Minify JSON: JavaScript, Python, jq, and When It Is Worth It
Minify JSON with JSON.stringify, Python json.dumps, jq, or a browser-local tool. Learn what changes, what does not, how compression affects savings, and when readable JSON is better.
11 min readJSON Viewer vs JSON Formatter: Which Tool Should You Use?
Compare JSON viewers and JSON formatters with practical examples for API debugging, large payloads, DevTools, jq, Prettier, diffs, repair workflows, and browser-local privacy.
11 min readFix "[object Object] is Not Valid JSON": Causes and Safer Syntax Fixes
Fix "[object Object] is not valid JSON" by finding where a JavaScript object was coerced to a string, then handle the related JSON syntax errors safely.
11 min readHow Online JSON Repair Works: Rules, Limits, and Safer Fixes
Learn how online JSON repair tools fix trailing commas, single quotes, unquoted keys, comments, Python literals, and LLM code fences without hiding risky data changes.
10 min readJSON Format Examples: Valid Objects, Arrays, API Responses, Config Files, and Edge Cases
Copy valid JSON examples for objects, arrays, API responses, config files, dates, nulls, escaped strings, JSON Lines, OpenAPI, GeoJSON, and common syntax mistakes.
11 min readHow to Format JSON Safely: Pretty-Print, Sort Keys, and Avoid Data Changes
Format JSON with JSON.stringify, Python json.dumps, jq, Prettier, VS Code, or a browser-local tool, with examples for indentation, sorting keys, validation, and safe workflows.
11 min readWhat Is JSON? Format, Syntax & Data Types
What JSON is, how the format works, its six value types, strict syntax rules, .json files, parsing, validation, and practical modeling choices.
13 min readDon't Paste Sensitive JSON Into Online Tools: Use Local Parsers
Sensitive JSON can leak through formatter logs, analytics, caches, tickets, screenshots, and browser extensions. Learn what not to paste, how to verify browser-local tools, and how to redact safely.
12 min readBad Control Character in JSON: Fix Raw Newlines, Tabs, NULs, and ANSI Bytes
Fix bad control character JSON errors by finding raw tabs, newlines, carriage returns, NUL bytes, and ANSI escape bytes inside strings, then escaping or removing them safely.
11 min readUnexpected Token o in JSON at Position 1: Fix [object Object] Parsing
Fix Unexpected token o in JSON at position 1 by finding the object, Response, Promise, Axios result, FormData, localStorage value, or already-parsed JSON that was passed to JSON.parse().
11 min readUnexpected End of JSON Input: Causes, Fetch Fixes, and Safe Parsing
Fix SyntaxError: Unexpected end of JSON input in JSON.parse(), fetch(), empty 204 responses, localStorage, truncated bodies, unclosed brackets, streams, NDJSON, and production safe parsing.
11 min readBase64 Is Not Encryption: What It Hides, What It Does Not
Base64 is encoding, not encryption. See why passwords, JWT payloads, API keys, Basic Auth headers, URL data, and logs stay readable after Base64.
15 min readHow to Compare Two JSON Files Without Key-Order Noise
Compare two JSON files by parsing, sorting keys, ignoring formatting noise, and highlighting real added, removed, and changed values.
12 min readSingle Quotes in JSON: Why JavaScript Objects Parse and JSON.parse Fails
Single quotes are valid in JavaScript object literals, not JSON. Compare the exact syntax differences, conversion traps, JSON.stringify behavior, safe repair workflows, and when not to use eval.
12 min readTrailing Comma in JSON: Why JSON.parse Rejects { "a": 1, }
Fix trailing comma JSON errors in objects and arrays. Learn why JSON.parse rejects final commas, how to find them from parser messages, when JSONC or JSON5 is appropriate, and how to prevent them in CI.
11 min readFix JSON.parse Unexpected Token Errors: <, u, o, Quotes, Commas, Comments, and HTML
Diagnose JSON.parse unexpected token errors by the first token you received: HTML, undefined, [object Object], single quotes, trailing commas, comments, Python literals, BOMs, NaN, or truncated JSON.
12 min readHow to Handle Broken JSON in JavaScript: Parse, Repair, Validate
Handle broken JSON in JavaScript with safer JSON.parse wrappers, fetch response checks, localStorage guards, jsonrepair workflows, error positions, schema validation, and browser-local repair.
13 min readJSON.parse Source Access: context.source, BigInts, JSON.rawJSON, and LLM JSON
Use JSON.parse reviver context.source and JSON.rawJSON safely: feature-detect support, rescue large numeric IDs, serialize BigInts, and harden repaired LLM JSON output.
12 min read