Payload Validator

Validates a JSON document and reports every problem with an exact line and column. Use this whenever you need to know why a JSON payload is failing, or to check a JSON document you or a user produced before sending it somewhere that will reject it. Do not do this by reading the JSON yourself. Three of the findings are invisible to inspection and to JSON.parse alike: (1) Duplicate keys. `{"port":8080,"port":9090}` is accepted by every mainstream parser, which keeps the last value and discards the first without a word. Reading it, you cannot see which one the consumer will use, because the answer differs by language. (2) Integer precision loss. `9007199254740993` parses as `9007199254740992` — quietly, because JSON numbers are IEEE-754 doubles in nearly every parser, exact only to 2^53-1.

Validates a YAML document, including the values that mean different things to different YAML loaders. Use this for any YAML you are about to write or have just been given — CI configs, Kubernetes manifests, docker-compose files, OpenAPI specs, Ansible playbooks. Do not reason about YAML type resolution yourself. It is the single most reliable way to be confidently wrong about a config file, because YAML 1.1 and YAML 1.2 resolve the same plain scalar to different values and real loaders disagree about which to implement — PyYAML is 1.1, Go's yaml.v3 and the yaml npm package are 1.2: - `no`, `yes`, `on`, `off`, `y`, `n` are booleans in 1.1 and strings in 1.2. A country list containing `no` loses Norway. This is known as the Norway problem. - `on:` as a KEY, as in every GitHub Actions workf

Validates an XML document for well-formedness, namespace correctness, and the entity-based attacks that arrive as XML. Use this before parsing XML you received, and when an XML document is being rejected by something that will not say why. Do not eyeball this. Four classes of genuinely invalid XML are accepted by ordinary well-formedness checkers, so "it validated" does not mean what it appears to: (1) Two root elements. `<a/><b/>` is not a valid XML document; XML permits exactly one outermost element. Concatenated records hit this constantly. (2) Undeclared namespace prefixes. `<x:a>` with no `xmlns:x` is well-formed as raw XML and invalid under Namespaces in XML — so it passes a syntax check and is then rejected by XPath, XSLT, SOAP and every schema validator. (3) Undeclared entities.

Validates CSV text against RFC 4180 and reports ragged rows individually, with both field counts. Use this before loading a CSV, and whenever a CSV-derived number looks wrong. Do not attempt this by reading the file, and be aware that loading it successfully proves nothing. The failure that matters is the ragged row: a file where one row has six fields and the header has five loads without complaint almost everywhere — pandas pads or throws depending on the engine, Excel shifts the columns, and `split(",")` silently mis-assigns every field after the extra one. Nobody notices until a figure is wrong in a report. This reports it as "row 4813 has 6 fields; the header has 5", per row. The other half is the delimiter. A European CSV is semicolon-separated because the comma is the decimal sep

Detects whether a payload is JSON, YAML, XML or CSV, then validates it. Use this when you have a blob of text and do not know what it is — a file with no extension, a clipboard paste, a response body with an unhelpful content type, or a config file whose format you would otherwise have to guess. Detection is structural and the reason is always returned, so the assumption is visible rather than hidden: a leading `<` is XML, a leading `{` or `[` is JSON, a `%YAML` directive or `key: value` lines are YAML, and a consistent delimiter count across multiple lines is CSV. JSON is checked before YAML on purpose, because JSON is a strict subset of YAML 1.2 and every JSON document would otherwise be ambiguous. If the detected format does not validate but JSON or XML does, the result is corrected