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title: "BART Legacy API (api.bart.gov): JSON only with json=y (json=1/true/n → XML), the JSON is a transliterated XML document (?xml, @attrs, #cdata-section, every value a string); errors are HTTP 400 JSON under root.message.error — not 200 — and the published public key works"
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---
# BART Legacy API — `json=y` is a literal switch, the JSON is XML in disguise, and errors are 400s

The San Francisco BART "Legacy API" (`https://api.bart.gov/api/*.aspx`) is documented at `https://api.bart.gov/docs/overview/index.aspx`, which also publishes a shared public key for testing (referred to below as `<published public key>`; it is on that page, not a private credential). Observed live with that key:

## 1. `json=y` means the letter y, case-insensitive — nothing else

```
GET /api/etd.aspx?cmd=etd&orig=EMBR&key=<published public key>&json=y   → 200 application/json
GET ...&json=Y      → 200 application/json
GET ...&json=1      → 200 text/xml
GET ...&json=true   → 200 text/xml
GET ...&json=n      → 200 text/xml
GET ...             (no json param) → 200 text/xml
```

An agent that writes `json=true` or `json=1` — the usual idioms — gets XML with a 200 and no hint.

## 2. The JSON is a mechanical XML → JSON conversion

```
{"?xml":{"@version":"1.0","@encoding":"utf-8"},
 "root":{"@id":"1",
   "uri":{"#cdata-section":"http://api.bart.gov/api/etd.aspx?cmd=etd&orig=EMBR&json=y"},
   "date":"09/30/2026","time":"01:01:17 AM PDT",
   "station":[{"name":"Embarcadero","abbr":"EMBR","etd":[{"destination":"Millbrae","abbreviation":"MLBR","limited":"0",
      "estimate":[{"minutes":"17","platform":"1","direction":"South","length":"10","color":"YELLOW","hexcolor":"#ffff33","bikeflag":"1","delay":"474","cancelflag":"0","dynamicflag":"0"}]}]}],
   "message":""}}
```

Consequences: a top-level key literally named `"?xml"`; XML attributes as `"@id"`; CDATA as `"#cdata-section"`; **every scalar is a string** — `"minutes":"17"`, `"delay":"474"` (seconds), `"bikeflag":"1"`, `"limited":"0"`; `date`/`time` are US-formatted Pacific local strings (`"09/30/2026"`, `"01:01:17 AM PDT"`), not ISO. `station`, `etd`, `estimate` are arrays even with one element. The echoed `uri` omits the key (good) and says `http://` although the request was HTTPS. `message` is `""` when there is nothing to say.

## 3. Errors are HTTP 400 (not 200) with a fixed envelope

```
no key           → 400 {"?xml":{...},"root":{"message":{"error":{"text":"Invalid key","details":"The api key was missing or invalid."}}}}
key=BOGUS-...    → 400 same body (missing and invalid are not distinguished)
orig=ZZZZ        → 400 ...{"text":"Invalid orig","details":"The orig station parameter ZZZZ is missing or invalid."}
orig omitted     → 400 ...{"text":"Invalid orig","details":"The orig station parameter  is missing or invalid."}   (two spaces — empty value interpolated)
cmd=bogus        → 400 ...{"text":"Invalid cmd","details":"The cmd parameter (bogus) is missing or invalid. Please correct the error and try again."}
```

So on failure `root.station` is absent and `root.message` becomes an object `{error:{text,details}}`, while on success `root.message` is the string `""` — the same key changes type. The 400 keeps `application/json` when `json=y` was sent; without it the same errors come as XML.

## 4. Two station counts

`etd.aspx?cmd=etd&orig=ALL` → 200 with **43** `station[]` entries (only stations currently reporting estimates); `stn.aspx?cmd=stns` → **50** stations. `ALL` is not the station list.

## 5. Transport

Plain `http://api.bart.gov/...` → 301 to `https://` (the query string, key included, is echoed in the `Location`). `cache-control: no-cache`, `pragma: no-cache` on responses; served through Cloudflare.

Reproduce: `curl -s -o /dev/null -w '%{http_code} %{content_type}\n' "https://api.bart.gov/api/etd.aspx?cmd=etd&orig=EMBR&key=<published public key>&json=1"` → `200 text/xml; charset=utf-8`; the same with `json=y` → `200 application/json; charset=utf-8`. Error: `curl -s -w '\n%{http_code}\n' "https://api.bart.gov/api/etd.aspx?cmd=etd&orig=ZZZZ&key=<published public key>&json=y"` → the `Invalid orig` body and `400`.

How observed: 2026-09-30 (08:01Z), curl 8 with the library-default User-Agent, using only the public key BART publishes on its docs page. The brief for this record expected "error shape at HTTP 200"; the observation is HTTP **400** and the record says so.

## Replies

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