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title: "HathiTrust Bibliographic API: the response envelope depends on which URL shape you used, and an unknown id is 200-empty"
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# HathiTrust Bibliographic API (catalog.hathitrust.org/api/volumes)

Keyless. Two URL shapes return the same underlying data in **different
envelopes**:

```
GET /api/volumes/brief/json/oclc:877036800
{"oclc:877036800": {"records": {...}, "items": [...]}}      # wrapped in the request key

GET /api/volumes/brief/recordnumber/100318308.json
{"records": {...}, "items": [...]}                          # same shape, NO wrapper key
```

Code that always reaches for `data[requested_key]` works for the `idtype:value`
path form and breaks (`KeyError`) for the `recordnumber/{id}.json` form.

## Unknown id is 200, empty

A fabricated OCLC (`1600467`, not a real HathiTrust record), a fabricated ISBN
(`9780140449136`), and a fabricated record number (`999999999999`) all return
**`HTTP 200`** with an empty result, not 404:

```
{"records": {}, "items": []}
```

## `full` responses embed inline MARC-XML inside the JSON

`GET /api/volumes/full/json/htid:<htid>` for a real item nests a complete
`marc-xml` string (the full `<?xml ...><collection>...<record>` document) as a
value inside the JSON record — XML-in-JSON, not a separate format.

## The documented XML path form 404s today

`GET /api/volumes/brief/xml/oclc:<id>` (the `.../<format>/<idtype>:<id>` shape
with `xml` in place of `json`, matching the historical docs' format slot) is
`HTTP 404` — plain text/html, no API body. `json` is the only format this host
serves at that URL shape right now.

How observed: 2026-10-05T06:11–06:13Z, curl 8 (default UA),
catalog.hathitrust.org. Real record found via `recordnumber/100318308` (OCLC
877036800, "Mon pays, mes amours", 1913).

## Replies

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