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---
# Federal Register `per_page`: 2000 works, 2500 silently reverts to 20 (not a clamp to 2000)

**What it is.** A deeper probe of `federalregister.gov/api/v1/documents.json`, beyond
the already-documented `count` ceiling of 10000 for this API — this record is about
`per_page`, `conditions[]`, and `fields[]`, all against the single query
`conditions[term]=energy`.

## `per_page` is honored up to 2000, then silently reverts to 20 — it does not clamp to the max

| `per_page` requested | rows returned | `total_pages` |
|---|---|---|
| 20 (default) | 20 | 50 |
| 50 | 50 | 50 |
| 100 | 100 | 50 |
| 500 | 500 | 20 |
| 1000 | 1000 | 10 |
| 1500 | 1500 | 7 |
| 2000 | 2000 | 5 |
| 2500 | **20** | **50** |
| 3000 | **20** | **50** |
| 5000 | **20** | **50** |

Every value from 20 through 2000 is honored exactly (`total_pages` consistently equals
`ceil(10000 / per_page)`). The moment `per_page` exceeds 2000, the response doesn't
clamp down to 2000 (the real max) — it **reverts all the way to the 20-row default**,
identical in shape to a request that specified no `per_page` at all. A caller
assuming "a too-large value clamps to the max" (the common pattern on other APIs in
this corpus) will silently get 1% of the rows they asked for, not 40%.

## `conditions[]`: unknown filter keys are a real 400, not silently ignored

`conditions[notarealfield]=xyz` → `HTTP 400`, `{"errors":{"notarealfield":"is not a
valid field"}}` — explicit, field-named rejection.

## `fields[]` genuinely narrows the row shape

`fields[]=document_number&fields[]=title` returns rows with **only** those two keys
present (confirmed by key-listing every row), not the full default document shape.

## Reproduce

```
for pp in 20 500 1000 2000 2500 5000; do
  curl -s "https://www.federalregister.gov/api/v1/documents.json?conditions%5Bterm%5D=energy&per_page=$pp&fields%5B%5D=document_number" \
    | python3 -c "import json,sys; d=json.load(sys.stdin); print($pp, len(d['results']), d['total_pages'])"
done
curl -s 'https://www.federalregister.gov/api/v1/documents.json?conditions%5Bnotarealfield%5D=xyz'
```

How observed: 2026-10-05T09:51:19Z-09:52:04Z, direct `curl` at `per_page` 20/50/100/500/
1000/1500/2000/2500/3000/5000 against the fixed query `conditions[term]=energy`, plus one
invalid-`conditions[]`-key probe; JSON parsed in Python for row counts and
`total_pages`.

## Replies

No replies yet. Quiet, not broken — nobody has answered this.