JSON Content Checker

Fetch any list of JSON endpoints or .json files and get a clean, structured check of each one — is it valid JSON, what's its shape, has it changed, and do the values you expect actually hold? Built for bulk: pass one URL or a thousand, and every URL becomes one check record. No API key required (optional custom headers let you check protected endpoints).

What it's for

• API & endpoint monitoring — confirm a JSON API still returns 200 and valid JSON on a schedule, and catch the moment it breaks.
• Change detection — every record includes a stable contentHash. Diff the hash across scheduled runs to know instantly when a feed's content changed.
• Data-contract / schema checks — assert that required paths exist (data.results, meta.total) and that values are in range (data.total > 100, status == "ok") across many endpoints at once.
• Bulk QA & pipelines — validate a whole list of JSON files or microservice responses in one run and export clean JSON for your dashboards.

Input

Field	Type	Description
urls	array	JSON endpoints / .json URLs to check. A missing scheme defaults to https://. Each URL produces one record.
requiredPaths	array	Optional. Dot/bracket paths that must exist in each document, e.g. data.results, items[0].id. Reported as present/missing with type + preview.
expectations	array	Optional. Value assertions, e.g. status == "ok", data.total > 100, items contains "foo", meta.next missing. Each is reported as passed/failed with the actual value.
requestHeaders	object	Optional. Extra HTTP headers sent with every request (e.g. an Authorization token for protected JSON).
followRedirects	boolean	Follow redirects and check the final destination. Default true.
timeoutSecs	integer	Per-request timeout in seconds. Default 30.
maxResults	integer	Safety cap on URLs checked per run. Default 1000.

Expectation syntax

One assertion per entry. The left side is a path; the right side a JSON literal (number, "string", true/false/null).

status == "ok"          data.total > 100        items[0].id exists
version != "0"          meta.count <= 50        results missing
title contains "Report" tags contains "news"    data.ok == true

Supported operators: exists, missing / present, ==, !=, >, <, >=, <=, contains.

Output

One record per URL:

{
  "url": "https://jsonplaceholder.typicode.com/todos/1",
  "finalUrl": "https://jsonplaceholder.typicode.com/todos/1",
  "success": true,
  "statusCode": 200,
  "contentType": "application/json; charset=utf-8",
  "declaredJson": true,
  "validJson": true,
  "jsonError": null,
  "rootType": "object",
  "topLevelKeys": ["userId", "id", "title", "completed"],
  "topLevelKeyCount": 4,
  "arrayLength": null,
  "itemCount": 4,
  "sizeBytes": 83,
  "depth": 1,
  "contentHash": "sha256:8e3f...c1",
  "hashMode": "canonical-json",
  "pathChecks": [
    { "path": "title", "exists": true, "type": "string", "valuePreview": "\"delectus aut autem\"" }
  ],
  "expectationResults": [
    { "expression": "id == 1", "path": "id", "operator": "==", "expected": 1, "actual": 1, "passed": true }
  ],
  "checksPassed": 2,
  "checksTotal": 2,
  "allChecksPassed": true,
  "fetchedAt": "2026-06-14T00:00:00+00:00",
  "error": null
}

How the content hash works

For valid JSON, contentHash is a SHA-256 of the canonicalized document (keys sorted, whitespace removed), so cosmetic reordering or reformatting never registers as a change — only real content does. For non-JSON responses, the hash falls back to the raw bytes (hashMode: "raw-bytes"). Run the actor on a schedule and compare contentHash between runs to detect when a feed actually changed.

Notes

• A non-JSON response is not an error — it's a real result: validJson is false, jsonError explains why, and the row is still returned (and charged).
• A URL that fails to fetch (timeout, DNS error, connection refused, bad URL) is recorded with success: false and the reason — it never crashes the run and is never charged.
• Paths support dot and bracket notation, including array indices (items[0].id) and quoted keys (data["weird.key"]).
• topLevelKeys is capped at the first 100 keys for very wide objects; topLevelKeyCount always reflects the true total.