There are tools out there for self-diagnosis but should you use them? Should you self-diagnose or should you see a professional?
Depending on where you live, there are lots of resources out there for kids on the spectrum. These can include;
If you have a child who may be on the spectrum, or if you're still at education age (early years of university) then getting a diagnosis is highly recommended.
As a general rule, adults get no special consideration for being on the spectrum. There will be some exceptions to this rule but for the most part, the exceptions are based on non-autistic criteria, such as the results of IQ tests or income and living conditions.
This means that getting a formal diagnosis as an adult doesn't provide a great deal of benefit past the written diagnosis itself.
If you feel that something just isn't right with your life and you can't proceed without a formal diagnosis, then it's highly recommended that you get one. A formal diagnosis can lead to a lot of "aha" moments that can put your life and decisions into perspective. Sometimes this is enough to enable people to turn around from difficult circumstances.
A diagnosis certainly isn't cheap and it will often come with extra costs, including potentially medication costs and extra visits to the doctor. Many medications used in autism require regular visits to a psychologist for prescription. Usually these costs are not met by public health systems.
If you don't need the diagnosis but simply want to know because of your children, work or family situations, then consider the self-diagnosis tools.