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". D77 is multiple cause 1999-2020 (MCD codes go in finder V13, plus O_mcd=D77.V13). D157 (single race, 2018-2024, final) answers both underlying (V2) and multiple cause (V13) and needs MORE V_ variables than D76 (V13/V15/V16/V26 + their _AND, V18, V30, V31, V42-V45) and O_race=D157.V42 — omit O_race and it 500s with "To Group Results By {0} you must also select the {1} button". Verified 2026-10-03: D76/D77 and D157 give identical deaths and population for 2018-2020 (all-cause, G37.2 underlying, G37.2 multiple cause). (7) "Suppressed" withholds a count (1-9); "Unreliable" blanks only a rate (<20 deaths) — the count is still released.