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JSON vs JSON5

JSON (RFC 8259) is the strict standard: keys must use double quotes, no comments, no trailing commas. JSON5 is a developer-friendly superset: allows unquoted keys, single quotes, comments, and trailing commas. Use JSON for APIs and data interchange; JSON5 for config files where humans edit.

Updated May 2026 · 4 min read
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Definition

JSON (RFC 8259) is the strict standard: keys must use double quotes, no comments, no trailing commas. JSON5 is a developer-friendly superset: allows unquoted keys, single quotes, comments, and trailing commas. Use JSON for APIs and data interchange; JSON5 for config files where humans edit.

What it means

RFC 8259 strict JSON requires: double-quoted strings only, no comments anywhere, no trailing commas, no special characters unescaped. Developer pain points: can&rsquo;t add explanatory comments to config files, trailing commas in arrays/objects cause errors, copy-paste from JavaScript breaks. JSON5 relaxes these: <code>// line</code> and <code>/* block */</code> comments allowed, single quotes allowed, trailing commas allowed, hex numbers (0xFF) allowed, multi-line strings via line continuation. Most major projects (Babel, RollupJS, Bun, ESLint config) accept JSON5 for config. APIs typically still require strict JSON.

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Why it matters

Config files written in JSON5 are dramatically more maintainable: comments document why, trailing commas survive line-rearrangement, single quotes match JavaScript style. Tools that accept JSON5 are signaling they value developer ergonomics. Tools that strictly require JSON are typically older or have backwards-compatibility constraints. JSONC (JSON with comments only) is a middle ground used by VS Code settings, tsconfig.json — strict JSON syntax PLUS line/block comments.

Example

JSON: <code>&#123;&quot;name&quot;: &quot;ada&quot;, &quot;active&quot;: true&#125;</code>. JSON5: <code>&#123; name: &lsquo;ada&rsquo;, // creator account active: true, &#125;</code>. Both represent the same data; JSON5 is more readable and tolerates trailing comma + comment.

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Frequently asked questions

When is JSON5 NOT appropriate?

API responses (clients expect strict JSON), database storage where the column type enforces strict, log files parsed by other tools that don&rsquo;t support comments. Always send strict JSON over the wire.

Can I parse JSON5 in JavaScript?

<code>JSON.parse()</code> doesn&rsquo;t support JSON5. Use the <code>json5</code> npm package: <code>const json5 = require(&lsquo;json5&rsquo;); json5.parse(input);</code>. Or pre-process input to strip comments / convert quotes before passing to <code>JSON.parse()</code>.

What about JSONC?

JSONC = JSON with Comments. Less permissive than JSON5 — only adds line and block comments, doesn&rsquo;t allow unquoted keys or single quotes. Used by VS Code and TypeScript config files. Easier to support in tooling than full JSON5.

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