How long is the job-search permit valid after a Master's in Germany?

Up to 18 months. If you have successfully completed your Master's (or another degree) in Germany, you can get a residence permit to look for work for up to 18 months (§ 20 (1) no. 1 AufenthG). It cannot be extended beyond 18 months, and you need a secured livelihood.

Apply at the Ausländerbehörde before your student permit expires: if you do, your current permit is deemed to continue until the decision (§ 81 (4) AufenthG). If you find a suitable job during this time, you apply to switch to a work-based residence permit. If you have not found a job within 18 months, check early whether you meet the requirements for another permit (e.g. further studies); for a job search from abroad, separate routes exist, such as the Opportunity Card (Chancenkarte, since 01.06.2024).

Source: § 20 AufenthG