JSON Formatting Best Practices for Developers

JSON is the lingua franca of web development. APIs speak it, config files use it, databases store it. Yet developers regularly waste time on avoidable JSON issues — trailing commas, mismatched brackets, encoding problems, and unreadable minified blobs. Here are the best practices that save time every day.

Validate Early, Validate Often

The single most common JSON debugging workflow is: something broke, the error message is unhelpful, and the root cause turns out to be malformed JSON. A missing comma, an extra bracket, a single quote instead of a double quote.

Best practice: Run your JSON through a validator before using it. Do not assume that because the data "looks right" it parses correctly. JSON is strict — no trailing commas, no single quotes, no comments, no undefined values.

Common validation errors and their causes:

| Error | Likely Cause | |-------|-------------| | Unexpected token | Trailing comma after last array/object element | | Unexpected string | Missing comma between key-value pairs | | Expected double-quoted property name | Single quotes used instead of double quotes | | Unexpected end of JSON input | Missing closing bracket or brace | | Bad control character in string literal | Unescaped newline or tab in a string value |

The BlestLabs JSON Formatter validates as you type and highlights the exact line and character where parsing fails.

Formatting for Readability

Minified JSON is great for network transfer but terrible for human comprehension. When debugging, always work with formatted JSON.

Indentation: Two spaces is the most common convention in web development. Four spaces is used in some Python ecosystems. Tabs are rare for JSON. Pick one and be consistent within your project.

Key ordering: JSON does not guarantee key order, but sorted keys make diffs cleaner and manual scanning faster. Many formatters offer an option to sort keys alphabetically.

Line length: If a JSON object fits on one line and is under ~80 characters, keeping it inline is fine. Beyond that, break it into multiple lines. Most formatters handle this automatically.

Minification for Production

Before sending JSON over the network, strip all unnecessary whitespace. The size savings can be significant — a well-formatted 50KB JSON file might minify down to 30KB.

When to minify:

• API response bodies
• JSON payloads in POST requests
• Configuration shipped to the browser
• Data stored in databases or caches where size matters

When NOT to minify:

• Config files checked into version control (readability matters for code review)
• Log output (you will need to read this at 3 AM)
• Documentation examples

Handling Common JSON Pitfalls

Trailing Commas

JavaScript allows trailing commas in objects and arrays. JSON does not. This is the number one source of "it works in my code but the API rejects it" bugs.

// INVALID JSON
{ "name": "Alice", "age": 30, }

// VALID JSON
{ "name": "Alice", "age": 30 }

Comments

JSON does not support comments. If you need commented configuration, consider JSON5, JSONC (used by VS Code), YAML, or TOML. If you must use standard JSON, a common workaround is a "_comment" key, though this pollutes your data structure.

Large Numbers

JSON numbers are IEEE 754 double-precision floats. Numbers larger than Number.MAX_SAFE_INTEGER (2^53 - 1, or 9007199254740991) lose precision when parsed by JavaScript. If you work with large IDs (like Twitter snowflake IDs), send them as strings.

Unicode and Encoding

JSON must be UTF-8 encoded (RFC 8259). Characters outside the Basic Multilingual Plane (emoji, some CJK characters) should work fine in any compliant parser, but be careful when passing JSON through systems that assume ASCII.

JWT Tokens Are JSON

A JWT (JSON Web Token) is three Base64-encoded JSON objects joined by dots. The header and payload are plain JSON — no encryption. Decoding them is trivial and essential for debugging authentication issues.

What to check in a JWT:

• exp (expiration) — is the token still valid?
• iat (issued at) — when was it created?
• sub (subject) — who is this token for?
• aud (audience) — which service should accept it?
• Custom claims — roles, permissions, tenant IDs

The BlestLabs JWT Decoder parses all three sections, formats the JSON payloads, and warns you if the token is expired.

Debugging API JSON Responses

When an API returns unexpected data, follow this sequence:

1. Copy the raw response — use your browser's Network tab or curl -v
2. Validate it — make sure it is actually valid JSON (APIs sometimes return HTML error pages with a 200 status)
3. Format it — expand the JSON so you can read the structure
4. Check types — is that "123" a string or should it be the number 123?
5. Check nulls — is a field missing entirely, or present with a null value? These are different things

Tools That Help

Keep these bookmarked:

• JSON Formatter — format, minify, validate
• JWT Decoder — decode and inspect tokens
• JSON to TypeScript — generate types from API responses
• Base64 Encoder — decode Base64-encoded JSON payloads
• Text Diff Checker — compare two JSON responses side by side

All of these run in your browser with no server-side processing. Your API keys, tokens, and data stay on your machine.