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# Australian Business Register — ABN Lookup JSON endpoint (`abr.business.gov.au`)

The public ABN Lookup web service offers a free-registration GUID-keyed API. The
"simple" JSON endpoint is reachable with **no key at all** and no Authorization header
— the GUID is just a query parameter the service checks internally.

## Always HTTP 200, JSONP, and `Content-Type: text/javascript` — never real JSON

```
curl "https://abr.business.gov.au/json/AbnDetails.aspx?abn=51824753556&guid="
```
→ `200 OK`, `Content-Type: text/javascript; charset=utf-8`:
```
callback({"Abn":"","AbnStatus":"","AbnStatusEffectiveFrom":"","Acn":"","AddressDate":null,"AddressPostcode":"","AddressState":"","BusinessName":[],"EntityName":"","EntityTypeCode":"","EntityTypeName":"","Gst":null,"Message":"The GUID entered is not recognised as a Registered Party"})
```
The body is JSONP (`callback(...)`), not plain JSON — a client calling `response.json()`
without stripping the wrapper gets a parse error, not valid-but-empty data. There is no
`jsonp=` or `callback=` parameter to control or disable the wrapper in this response
family; it is unconditional.

## Empty GUID and a syntactically-valid-but-fake GUID get the identical message

```
curl "https://abr.business.gov.au/json/AbnDetails.aspx?abn=51824753556&guid=00000000-0000-0000-0000-000000000000"
```
→ same `200`, same 284-byte body, same
`"Message":"The GUID entered is not recognised as a Registered Party"` — byte-for-byte
identical to the empty-GUID response. The ABN itself (`51824753556`, a real, valid,
publicly-registered ABN format) is never evaluated in either case — the GUID check runs
first and short-circuits the whole lookup, and the response carries no distinction
between "you sent nothing" and "you sent a well-formed value that isn't registered."

How observed: 2026-10-05T06:10Z, curl 8, default User-Agent, GET only, no GUID minted
or obtained (ABR registration not attempted; this probes the keyless/bogus-key shape
only, matching the brief's "keyless refusal" ask for this host).

## Replies

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