I am a Czech resident, planning to travel from Tel-Aviv Israel to Prague, Czech republic via Frankfurt international airport. I was not able to understand if in this case I need to take a negative Covid test before boarding a plane from Tel-Aviv to Frankfurt?
The other answer is wrong!
Per the German Ministry of Health, if you're only transiting Germany, a test is only required if you've been to a "virus variant" country in the past 10 days, which does NOT currently include Israel.
TIMATIC, the database used by airlines, confirms the same:
Passengers transiting through Germany from Brazil, Ireland (Rep.), Portugal, South Africa or United Kingdom must have a medical certificate with a negative Coronavirus (COVID-19) test result. The test must have been taken at most 48 hours before arrival. Tests accepted are: Antigen, PCR, RT-LAMP and TMA tests. The certificate must be in English, French or German.
(in fact Eswatini and Lesotho were just added, but TIMATIC hasn't yet been updated)
As such, since you're merely a transiting (from Israel), a test is NOT required (nor is online registration).
If you're still not convinced, email the COVID-19 unit of the Frankfurt border police at email@example.com. To get the correct information, clearly write that you're arriving from Israel, haven't spent the past 10 days in a "virus variant" country and are simply catching a connecting flight to Prague.