Why compare?

The crypto_* functions (CoinMarketCap) and the cg_* functions (CoinGecko) are deliberately interchangeable – column names, sort order and types match – so the same downstream code consumes either tibble. For empirical work the right thing to do is to always cross-check a metric across both sources. Doing so:

• catches silent schema regressions on either platform;
• catches unit-of-quote bugs (USD vs sats vs cents);
• catches calendar / date-labelling errors;
• and gives factor pipelines a robustness buffer when one provider changes its policies.

The date-convention pitfall

A subtle but important detail: the two providers label the same physical instant with different dates.

These two instants are essentially the same moment in time (they differ by 1 second), but the date labels disagree by one day. The first convention is the standard asset-pricing convention (CRSP, Compustat, Liu/Tsyvinski/Wu 2022 and most academic work): under it, close[X] / close[X-1] - 1 is the return earned during date X.

cg_history() and cg_history_by_id() ship with date_convention = "end_of_day" as the default, which shifts CG’s midnight-UTC ticks by -1 day so the output lines up with CMC’s labels. Pass date_convention = "raw" to keep CG’s native start-of-day labels (useful when you are doing diagnostic work directly against the CoinGecko UI or its public API).

# default: CMC / CRSP / Compustat convention
btc_cg <- cg_history(coin_list = tibble::tibble(slug = "bitcoin", id = 1L),
                     start_date = "2026-05-01")

# raw: CG's start-of-day labels
btc_cg_raw <- cg_history(coin_list = tibble::tibble(slug = "bitcoin", id = 1L),
                         start_date  = "2026-05-01",
                         date_convention = "raw")

A worked example: Bitcoin reconciliation

library(crypto2)
library(dplyr)
library(tibble)

start_date <- Sys.Date() - 10
end_date   <- Sys.Date()
btc_anchor <- tibble::tibble(id = 1L, slug = "bitcoin",
                             name = "Bitcoin", symbol = "BTC")

cmc <- crypto_history(coin_list = btc_anchor, convert = "USD",
                      start_date = start_date, end_date = end_date) |>
  transmute(date = as.Date(timestamp), close_cmc = close)

cg <- cg_history(coin_list = btc_anchor, convert = "USD",
                 start_date = start_date, end_date = end_date) |>
  transmute(date = as.Date(timestamp), close_cg = close)

joined <- inner_join(cmc, cg, by = "date") |>
  mutate(pct_diff = (close_cg - close_cmc) / close_cmc * 100) |>
  arrange(date)

joined
#> # A tibble: 10 x 4
#>    date       close_cmc close_cg  pct_diff
#>    <date>         <dbl>    <dbl>     <dbl>
#>  1 2026-05-08    80187.   80189.  0.003
#>  2 2026-05-09    80664.   80678.  0.017
#>  3 2026-05-10    82139.   82146.  0.008
#>  ...

Typical agreement on BTC is well under 0.05% per day, with occasional spikes up to ~0.5% in periods of high intra-day volatility (the two providers compute their daily close from slightly different exchange-weighting baskets). If you ever see >1% on BTC, something is wrong – start by double-checking your date_convention argument.

What’s expected to differ – and what isn’t

Use price for cross-validation; treat volume and market-cap-via-supply disagreements as informative on their own.

The built-in test

tests/testthat/test-cg-vs-cmc.R runs a tight reconciliation on BTC (7-day window, tolerance 1%) on every CI run that has network access. It will fail loudly if the date conventions ever drift out of alignment again, or if either provider switches its underlying basket significantly enough to break the tolerance.

When to override the default

The "end_of_day" default is what you almost always want. Switch to "raw" when:

• you are reproducing a CoinGecko chart published with start-of-day labels;
• you are debugging the raw data parsing inside cg_history();
• you are comparing daily CG output side-by-side with a Demo /coins/{id}/market_chart call (which also returns start-of-day timestamps).

Otherwise, leave it alone and join cleanly with crypto_history() output on as.Date(timestamp).