StrictlyBetter offers information about Magic the Gathering cards that are functionally superior to other cards.

Using the the site a MTG player may search for better card alternatives for their older deck or cards that may have been printed without putting in too much effort. For example, they may want to upgrade their Murder to Hero's Downfall.

The site also has an API, so other developers may further use the suggestion data as they wish.

Where is the data coming from?

The suggestions listed on the site are added via Add Suggestion page by anonymous Magic the Gathering players.
Adding new suggestions and voting for them requires no login or account.

Some suggestions are also generated programmatically. Due to complex rules of the cards, only cards with identical rules are considered when evaluating strict-betterness this way.

The card database is downloaded from Scryfall using their bulk-data files

Adding new suggestions

New suggestions have to pass a few automated checks, however, rules texts of the cards are not evaluated automatically (except for functional reprints).
As a community run site, the validation of card "betterness" is ultimately left to users and the voting system.

Any suggestions with following conditions are automatically rejected

Labels and searching

When browsing, you may see labels on card suggestions indicating there might be cases the suggestion is not a strictly better choice.
Suggestions with labels are still listed when searching as they may still be useful when considering card replacements, unless you specifically hide them via filter menu on the Browse page.

List of current labels:

The "strictly better" controversy

People have disagreements about what constitutes as "strictly better". So it is good to remember the site is primarily a tool for finding better options. Other than automated rules and labels/filters mentioned above, StrictlyBetter makes no ruling over what is truly strictly better, as I believe it is better to have the voters decide.

Personally I prefer card suggestions that are better when considered in a vacuum. (Without knowledge of the deck it is played in or decks it's facing)
This outlines a few base rules like: opponents card to exile > graveyard, "each" > "target 3", double strike > first strike

How to contact the developer

Site is run by Henri Aho. You may contact me at henrij.aho@gmail.com
There is also a Reddit thread about the site.