Please help what? you want us to write it for you? if so, and you are willing to pay for it, contact me, if not, don't bother to contact me...
Really didn't specify much in this thread at all. Can it be coded using JavaScript? Is there any other restrictions to it. What specific types of META tags are you trying to generate? etc. Not to mention I'm not sure why you wouldn't use PHP considering it would be extremely simple using PHP and your source code would be virtually safe. However, if you don't know how to make something as simple as a META tag generator what makes you think you would be able to run a site that can out do all the thousands of pre-existing sites? If you're trying to build a site to drive people to you need to quit reinventing the wheel.
In that case you should of asked for a revenue generating web site.... not a useless meta tag generator