how long  can I keep uncooked lentils in my pantry? 
Lentils are good for a long time: Many claim that they stay safe "indefinitively".  While that is clearly an exaggeration, properly stored lentils stay edible for years if you keep them well-sealed in a cool, dry and dark(-ish) place.  Note that dry storage keeps mold at bay, closed jars protect from insect damage and cool temperatures slow trace amounts of fat getting rancid. They might get tough and a bit stale, but that can be mitigated by cooking longer and a generous hand when seasoning.  To add one source (for completeness): Still Tasty gives one year but states that it doesn't get unsafe, simply looses taste.  