JSON Validator & Formatter — Bulk JSON Parsing, Pretty-Print, Minify

Validate and format JSON from inline strings or URLs in a single Apify run. Catch syntax errors with byte-position context, get pretty-printed and minified output, and compute structural stats (object/array/depth/key counts, sizes, compression ratio) per input.

This actor uses Node's built-in JSON.parse — strict spec compliance, no schema validation, no auto-fix transforms. If you need JSON Schema validation, comment-stripping, or NDJSON streaming, request a custom build.

Use cases

• API QA — validate batches of API responses in one run, surface broken endpoints
• ETL gate-check — verify upstream JSON before downstream stages corrupt warehouse loads
• Bulk formatter — pretty-print or minify many payloads with consistent indent
• Spec drift detection — diff stats (key counts, depth) across runs to catch schema changes

Inputs

Field	Type	Description
jsonStrings	string[]	Inline JSON strings to validate
urls	string[]	URLs that return JSON. Strings without scheme get https:// auto-prepended. Fetched via fetch, single attempt, no retries, NO timeout (long-hanging URLs will block the run)
indent	integer	Spaces for pretty-printing (1–8, default 2)

Either or both arrays can be populated. Empty inputs → no work done.

Output (per input)

Field	Type	Notes
source	string	URL or "input" for inline strings
isValid	boolean	JSON.parse success
formatted	string | null	Pretty-printed (null if invalid)
minified	string | null	Whitespace-stripped (null if invalid)
error	string | null	Parse error message
errorPosition	number | null	Byte offset of first parse error. Extracted via regex /position (\d+)/ against JSON.parse's error message — the format is Node-version-dependent (v17+ reliably emits "at position N"). Older Node versions may return a different format and errorPosition will then stay null even though error carries useful text.
errorContext	string | null	±20 chars around errorPosition (max 40 chars)
stats	object | null	See below — present only when isValid: true
scrapedAt	string	ISO timestamp

For URL-fetch failures (network error, DNS fail, refused connection), the record is abbreviated: only source, isValid: false, error, scrapedAt — no formatted/minified/stats/errorPosition/errorContext keys at all (asymmetric vs. parse-failure records). Normalize explicitly if you join.

stats object (always emitted with all 12 fields — leaf-type counters default to 0 even when none present):

Field	Type	Description
objects	number	Total {} nodes
arrays	number	Total [] nodes
strings / numbers / booleans / nulls	number	Leaf-type counts (0 if none — explicitly emitted)
totalKeys	number	Sum of object keys across all levels
maxDepth	number	Deepest nesting level (0 = root scalar, N for N-deep nesting)
originalSize	number	Input length (chars)
formattedSize	number	Pretty-printed length
minifiedSize	number	Minified length
compressionRatio	number	minified / formatted (typically 0–1; small docs may exceed 1 if formatted is artificially compact)

Example input

{
  "jsonStrings": [
    "{\"name\":\"test\",\"items\":[1,2,3]}",
    "{ broken: 'json',"
  ],
  "urls": [
    "https://api.github.com/repos/vercel/next.js",
    "https://httpbin.org/json"
  ],
  "indent": 2
}

Example output (one valid record)

{
  "source": "input",
  "isValid": true,
  "formatted": "{\n  \"name\": \"test\",\n  \"items\": [1, 2, 3]\n}",
  "minified": "{\"name\":\"test\",\"items\":[1,2,3]}",
  "error": null,
  "stats": {
    "objects": 1,
    "arrays": 1,
    "strings": 1,
    "numbers": 3,
    "booleans": 0,
    "nulls": 0,
    "totalKeys": 2,
    "maxDepth": 2,
    "originalSize": 31,
    "formattedSize": 41,
    "minifiedSize": 31,
    "compressionRatio": 0.756
  },
  "scrapedAt": "2026-04-29T10:30:00.000Z"
}

Limits & honest caveats

• No JSON Schema validation. Only JSON.parse strictness.
• No auto-fix. Comments, trailing commas, single quotes, unquoted keys → invalid.
• URL fetch is single-attempt with NO timeout. Node's global fetch has no default timeout — a hanging URL will block the run until Apify's wall-clock kills it. No retries on transient errors.
• No proxy. URL fetches go out from Apify's compute IP directly.
• No HTTP status check before parse. A 404 HTML error page is fetched as text and fed to JSON.parse, which fails with a parse error rather than a network error. This is correct behavior for "is this URL returning valid JSON?" questions but counter-intuitive when triaging — check error content carefully.
• No NDJSON / JSON-Lines mode. Each input must be one complete JSON document.
• Big-int precision loss. JSON.parse returns JavaScript Numbers. Integers larger than 2^53 (9,007,199,254,740,992) lose precision silently — common with database PKs serialized as raw integers in some APIs. Pre-process such inputs to strings if precision matters.
• Apify pushData record cap (~9 MB per record). Very large formatted/minified outputs from a single huge JSON input may be truncated by the platform. Split into chunks for >9 MB documents.
• errorPosition is best-effort. Depends on Node v17+ error-message format; will be null on older runtimes.

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Apify-as-a-Service — when you need data, not infrastructure

Tier	Price	What you get
Pilot	$97	1 custom actor, basic config, 7-day support
Standard	$297	Custom actor + Slack/email alerts, 30-day support
Premium	$797	Custom actor + dashboard + 90-day support + 1 modification round

A custom build can deliver: JSON Schema (Ajv) validation with full error reporting, NDJSON / JSON-Lines streaming, comment / trailing-comma tolerant parsing (json5), big-int support via JSON.parse reviver, fetch retry+timeout+proxy, recursive URL crawl with auth headers.

Email: spinov001@gmail.com — drop the validation rules, expected schema, or sample malformed inputs.

Proof of work: 31 published Apify scrapers (78 total in portfolio) — Trustpilot 949 runs, Reddit 80+, Google News 43, Glassdoor 37, Email Extractor 36+. Recently delivered a paid 3-article series for a client in the proxy industry ($150).

More tips: t.me/scraping_ai · blog.spinov.online

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All 31 published actors → apify.com/knotless_cadence

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Honest disclosure: 12-field stats always emitted (leaf counters default to 0). errorPosition depends on Node v17+ message format. Single-attempt fetch, no timeout, no retry, no proxy. URL records on fetch failure are abbreviated (no formatted/minified/stats keys). Big-int precision loss above 2^53. Apify pushData ~9 MB cap per record.