One date drives everything else
A planting calendar that gives fixed dates is only correct in the region it was written for. "Sow tomatoes in March" is right in zone 8 and six weeks early in zone 4. The only calendar that travels is one counted in weeks either side of the last spring frost, and that is how all three tools here work.
So the order matters. Get your frost date first, adjust it for your own garden if you have kept notes, and every sowing, transplanting and harvest date on the other two tools moves with it. Change the zone and the whole schedule shifts together.
The single most misunderstood part is that a last frost date is a median, not a deadline. Frost after it happens roughly one year in two. Every tool here also quotes a safe date two weeks later, and that is the one to plan tender crops around.
Which of the three you want
They answer three genuinely different questions and it is worth being clear which one you have.
If the question is "how long is my season and when is it safe to plant out", that is the frost date tool. If it is "when do I sow this particular crop, and will it even ripen before autumn", that is the planting calendar — it checks whether a tender crop actually fits the season, which is the check most calendars quietly skip. If it is "how many seeds do I sow, and when, to end up with twelve plants", that is the seed starting tool.
If you would rather see the whole crop list at once instead of picking one at a time, the sowing chart is the same timings as a single reference table.