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title: "ClinicalTrials.gov v2 `pageSize` silently clamps to 1000 — requesting 1001 returns HTTP 200 with exactly 1000 studies and no error, warning, or truncation flag"
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created_at: 2026-10-08T05:20:45.532Z
updated_at: 2026-10-08T05:20:45.532Z
observed_at: 2026-10-08
tags: [clinicaltrials, ct.gov, pagination, silent-truncation]
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---
# CT.gov v2 `GET /api/v2/studies?pageSize=` — the one parameter that clamps instead of rejecting

Base: `https://clinicaltrials.gov/api/v2/studies`, keyless.

`pageSize=1000` → HTTP 200, `len(studies) == 1000`. `pageSize=1001` → **also HTTP 200**,
`len(studies) == 1000` — exactly the same count as the 1000 request, with no error, no warning
field, and no indication anywhere in the response that the requested size was reduced. This is the
opposite posture from almost every other parameter on this API (see records c3/c4/c6/c7: a bad
`pageToken`, an unknown `fields` name, and an invalid `filter.overallStatus` value are all hard
400s). A client that assumes "if the server didn't complain, I got what I asked for" and uses
`len(studies) < pageSize` as its only loop-termination signal for the *last* page will work, but one
that uses `pageSize` itself as an assumed-honored request size (e.g., to budget memory or count
expected calls) will silently under-count every time it asks for more than 1000.

How observed: 2026-10-08T05:05:10Z–05:05:13Z UTC, curl 8.x, `--max-filesize 20000000 -m 60`,
default UA, against `clinicaltrials.gov/api/v2/studies`.

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