There's a bunch of words in my question that don't have tags yet. Can I just add them all?
Before you create that new tag, stop and consider the following:
Note: The example questions used here are intentionally basic and should not be taken as a guideline for what is appropriate to ask on the site.
1. Is this a useful way to categorize the question?
For example, if your question is "Why do rockets sometimes explode?", then rockets and rocket-explosion are probably both good tags, because someone looking in those categories is probably interested in that type of question.
However, let's say the body of your question says, "Some rockets have exploded in the air and others on the launchpad." air would not be a helpful way to categorize the question. Someone looking at questions about air is probably not interested in why rockets explode. In fact, launchpad may not be helpful either. Unless the question is seeking specific information about launchpad explosions, someone looking at questions about launchpads is probably not interested in why rockets explode either.
2. Is this concept useful for space exploration?
For example, if your question is "Do burgers taste different in space?", burger is probably not a useful tag. Short of some surprising turn of events (e.g. Bigelow launching a burger shop in space), there are probably not going to be a lot of questions about burgers on the site, and even if there were a few someone is unlikely to go looking for a burger category unless they already know about those questions. Consider: food
3. Will this tag get used again?
Categories are only useful if they gather a collection of related questions. Let's say your question is "Will the Laser Corp SuperZapBolt laser be used on the new satellite?" You might think lasercorp-superzapbolt passes #1 and #2, after all lasers aren't an unusual topic in space exploration. However, consider whether it is really likely that someone will be asking about this specific laser again. Has it been used on multiple existing spacecraft or very prominently on a well-known spacecraft? If not, it's probably not going to attract any other questions, and you should just stick with laser.
4. Is there an existing tag that is fairly equivalent in terms of categorizing the question?
5. Is the tag spelled right? Are you sure?
Similar to #4, this is about how well you check for existing tags. Please be absolutely certain you are using the correct spelling for all the words in your tag. Google them and copy and paste the exact spelling. Make sure tags with the correct spelling don't already exist. Also, keep in mind that we standardize on US English spellings for tags.
The flipside here is called burnination, where the community removes tags. It's worth reading what the overall methodology is, but you should pay attention that tags must be clear
We recently reversed a tag synonym because [neo] was potentially vague. I've seen that happen a lot, where a tag goes with an acronym or simple name, and thus you wind up with multiple meanings for the same tag. An excerpt can help, but not all users will see them (they don't show up on mobile), let alone read and obey them.