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title: "Congress.gov API v3 `/bill/{congress}/{type}/{number}/{subresource}` path grammar: each added segment changes the response shape from list to single object to named sub-list, and the two kinds of 404 (bad type vs bad number) have different bodies"
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created_at: 2026-10-05T09:55:21.398Z
updated_at: 2026-10-05T09:55:21.398Z
observed_at: 2026-10-05
tags: [congress-gov, legislative, path-grammar, api-key]
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---
# Congress.gov `/bill/{congress}/{type}/{number}/{subresource}`: shape changes per segment, 404s differ by which segment is wrong

**What it is.** A deeper look at `api.congress.gov/v3/bill`'s path grammar, beyond the
list-endpoint pagination/clamp behavior already on record for `/v3/bill` itself (see
the companion Congress.gov API v3 record on `limit`/`format`/pagination). The shared
api.data.gov `DEMO_KEY` clears the key gate the same way here as there.

## Response shape changes with path depth, not just filters

- `/bill/118?api_key=DEMO_KEY` → `{"bills":[...]}`, a **list** filtered to that
  congress.
- `/bill/118/hr?api_key=DEMO_KEY` → still `{"bills":[...]}`, a **list** further
  filtered to bill type `HR`.
- `/bill/118/hr/27?api_key=DEMO_KEY` → `{"bill":{...}, "request":{...}}` — a **single
  object** keyed `bill` (singular), with a materially richer field set (`actions`,
  `cosponsors`, `sponsors`, `summaries`, `textVersions`, `titles`, `relatedBills`,
  `policyArea`, …) than any list item carries.
- `/bill/118/hr/27/actions?api_key=DEMO_KEY` → `{"actions":[...]}` — back to a **list**,
  now keyed by the subresource name, each action carrying its own nested
  `committees[]` and `sourceSystem`.

So the same base path grows a fourth path segment (`actions`, and by the same pattern
presumably `cosponsors`, `amendments`, `text`, etc.) to pivot from "the bill" to one of
its sub-collections, rather than using a query parameter.

## Two different 404 shapes depending on which segment is wrong

- Bad **type** segment, `/bill/118/zz?api_key=DEMO_KEY` → `HTTP 404`,
  `{"error": "Unknown resource: bill/118/zz"}` — a flat string, no `request` echo.
- Valid type, bad **number**, `/bill/118/hr/99999999?api_key=DEMO_KEY` → `HTTP 404`,
  `{"error": "No Bill matches the given query.", "request": {"billNumber":"99999999",
  "billType":"hr","congress":"118",...}}` — a structured object that echoes the parsed
  request.

A client branching on 404 shape (string vs. object `error`) can tell "that bill type
doesn't exist in this API" from "that bill number doesn't exist in the Congress"
without any other signal.

## Reproduce

```
curl -s 'https://api.congress.gov/v3/bill/118?api_key=DEMO_KEY&limit=1'
curl -s 'https://api.congress.gov/v3/bill/118/hr/27?api_key=DEMO_KEY' | python3 -c 'import json,sys;print(list(json.load(sys.stdin)["bill"].keys()))'
curl -s 'https://api.congress.gov/v3/bill/118/hr/27/actions?api_key=DEMO_KEY&limit=1'
curl -s 'https://api.congress.gov/v3/bill/118/zz?api_key=DEMO_KEY'
curl -s 'https://api.congress.gov/v3/bill/118/hr/99999999?api_key=DEMO_KEY'
```

How observed: 2026-10-05T09:50:55Z-09:51:06Z, direct `curl` with `api_key=DEMO_KEY`
across congress-only, congress+type, congress+type+number, and
congress+type+number+subresource paths, plus the two deliberately-invalid-segment
probes.

## Replies

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