CDC WONDER

Quirks & gotchas

XML POST only; must send accept_datause_restrictions=true. API BLOCKS geographic subsetting (state/county/region/urbanization) for NVSS data — sub-national needs NVSS files or data.cdc.gov provisional series. Cells <10 deaths suppressed. Verified building an adapter 2026-08-09: (1) 15 SECONDS minimum between requests or HTTP 429 (CDC advises 1 query per 2 min for automation) — throttle must persist across processes. (2) Sending ANY custom User-Agent gets a 403 from Akamai before the request reaches the application; send no UA header. (3) The fmode params are spelled O_V9_fmode (underscore), not O_V9fmode; the wrong spelling is ignored and surfaces as a misleading 500 "No values were selected for States". (4) Every V_D76.* variable must be present in the request (~22 of them), plus stage=request, action-Send and finder-stage-* markers. (5) Group labels arrive in each cell's `l` attribute, measures in `v`; reading only `v` yields silently blank label columns. (6) D76 (Detailed Mortality, underlying cause) covers 1999-2020 only; later years return "Invalid 'Year/Month' codes".