つもり

Strongly Believe
Noun + のつもり
Plain form verb + つもり
(Adjectives not really used, see below)

つもり is a noun, and conjugates like a noun.
It expresses “Strongly believing something to be true”.
Its closest English equivalents are “intent”, “believe”, or “pretend”

Intend

つもり usually means “intend”.
The intent described by つもり is stronger than just “thinking about” or “Considering”.
It is closer to “Plan on” or “Strongly believe“

Examples

• 怒らすつもりはなかった – I didn’t intend to make you mad.
• 明日は合格するつもりだ – I intend to pass tomorrow. 
• 日本に行くつもりだ – Intention to go to Japan. 
• 告白するつもりだ – I intend to confess my feelings today. 

Pretend

Another use of つもり is to mean “pretend”. Literally it means something like “Intend a thing is true”.
This usage is rarer than “intention”. This meaning tends to be つもりで.

Examples

• 親のつもりでお世話する – Take care of them as if you (believed you) were their parents.
• 外食したつもりで外食したらかかるお金を貯金する – “Pretend” to have eaten out and save that money. 
• 犯人になったつもりで調べる – Investigate while pretending to be the culprit. (Think like)
  
  

Believed

Past tense + つもり typically translates as “Believe”.

Examples

• 質問をわかったつもりだったがわかっていなかった – I believed I understood it, but I didn’t. 
  (I intended to have understood, but didn’t. )
• 作ったつもりだったが、作っていなかったようだ – I believed I had made it, but apparently I didn’t. 
• やったつもりだ – I believe I did it. 

Adjectives

Since つもり is a noun, it should be able to be modified by adjectives as well, but I can’t think of nor find any examples of this. (For the meanings above)
Almost all of the time this pattern will use a verb if it can.
This is probably due to verbs being necessary for clarity:

やさしいつもりだ – A nice intention
優しくするつもりだ – Intention of doing it nicely.