yokatta よかった

In Japanese, yokatta よかった means a number of things depending on context. Used alone, yokatta means "that's a relief." It can also mean it was good you did something, or it would have been good if you had done something you didn't. And it's the past form of ii いい, so it means literally "was good."

Manga: Watashi ga Motenai no wa Dou Kangaetemo Omaera ga Warui! 私がモテないのはどう考えてもお前らが悪い！ (chapter 5)

Kanji

The word yokatta written with kanji is yokatta 良かった, but it's often written with hiragana, as yokatta よかった instead.

"Was Good"

To understand how yokatta works, let's start with its most literal meaning: "was good," the past form of ii いい, or rather, of yoi 良い, which means "good."

tenki ga ii 天気がいい
tenki ga yoi 天気が良い
The weather is good.
tenki ga yokatta 天気がよかった
The weather was good.

Expressions

Every expression which contains ii いい in Japanese can be turned into past by replacing it with yokatta よかった. For example:

un ga ii 運がいい
"Luck is good."
[You're lucky.]
un ga yokatta 運が良かった
"Luck was good."
[You were lucky.] (were it not for your luck you would have died right there.)

naka ga ii 仲がいい
"Relationship is good."
[They're friends.]
naka ga yokatta 仲がよかった
"Relationship was good."
[They were friends.]

kakko-ii カッコいい
"Good-looking."
[You're cool.]
kakko-yokatta カッコよかった
"Was good-looking."
[You were cool.] (that. Was. AWESOMEEEE~~~!!!)

kimochi-ii 気持ちいい
"Good-feeling."
Pleasant.
kimochi-yokatta 気持ちよかった
"Was good-feeling."
Was pleasant.

hou ga ii 方がいい
"Way is good."
Better if...
hou ga yokatta 方がよかった
"Way was good."
Was better if...

Talking About Past Events

The word yokatta よかった can be used to express regret or gladness about something that happened in the past. This comes from interpretations of its literal meaning, "was good," see:

You did something. It "was good" that you did it.
You didn't do something. It was bad that you didn't do it, because doing it "was good" and you didn't do it.

At first glance it can appear confusing, but it really isn't. In either case, the speaker is saying the action was a good idea. If he did the action, then he's glad he's done it. If he didn't do it, then he regrets not having done it. You can normally tell which one is it from the context.

~てよかった

When you have a verb in the te-form plus yokatta よかった, that is, -te yokatta ～てよかった, etc. it's usually the "regret" or "gladness" meaning. In case you don't know your te-forms, for reference:

shite yokatta してよかった
I'm glad I did.
- shite
  te-form of suru する,
  "to do."
kite yokatta 来てよかった
I'm glad I came.
- kite
  te-form of kuru 来る,
  "to come."
de yokatta でよかった
I'm glad [something] was [something]
- de
  te-form of da だ copula.
  Used after adjectives, nouns, etc.
mite yokatta 見てよかった
I'm glad I saw it.
- mite
  te-form of miru 見る,
  "to see."
yonde yokatta 読んでよかった
I'm glad I read it.
- yonde
  te-form of yomu 読む,
  "to read."

会えて良かったよ！ quote from manga Mob Psycho 100 モブサイコ１００ (chapter 67)

Manga: Mob Psycho 100, Mobu Saiko Hyaku モブサイコ１００ (chapter 67)

aete yokatta yo!
会えて良かったよ！
"Meeting was good."
I'm glad I met you.
- au 会う
  To meet.

～ばよかった

When you have a verb in the ba-form plus yokatta, that is, -ba yokatta ～ばよかった, then it's the regret meaning. That's because the ba-form is the conditional form: it's hypothetical, didn't actually happen. So you're saying it would have been good if something (which didn't happen) happened.

Manga: Watashi ga Motenai no wa Dou Kangaetemo Omaera ga Warui! 私がモテないのはどう考えてもお前らが悪い！ (chapter 5)

Context: it begins raining.
zaaaaa
ザァァァァ
*rain noises* (onomatopoeia.)
konna koto nara
konbini de kasa
kaeba yokatta
こんなことなら
コンビニで傘
買えばよかった
If it were to be something like this
it would have been better if I had bought
an umbrella at the convenience store.
- kaeba 買えば
  If bought.
  (ba-form of)
- kau 買う
  To buy.

Gladness

Some examples of yokatta meaning "I'm glad" for having done something:

ganbatte yokatta 頑張ってよかった
I'm glad I did my best.
I'm glad I put effort.
(because it paid off.)
- ganbaru 頑張る
  To try hard. To put effort. To try one's best.
hanashite yokatta 話してよかった
I'm glad we talked.
- hanasu 話す
  To talk. To have a conversation.
kiite yokatta 聞いてよかった
I'm glad I heard it.
I'm glad I asked.
- kiku 聞く
  To hear. To listen.
  To ask something.
ikite yokatta 生きてよかった
I'm glad I lived.
- ikiru 生きる
  To live.
  (one of the heaviest phrases you can make with yokatta.)
nyuubu shite yokatta 入部してよかった
I'm glad I joined this club.
(because of all the friendships, memories, et cetera I made along the way.)
- nyuubu 入部
  To enter a club.

無事でよかった quote from manga One Piece ワンピース (chapter 1)

Manga: One Piece, Wan Piisu ワンピース (chapter 1)

buji de yokatta
無事でよかった
I'm glad [you're] unharmed.
- de で
  te-form of da だ.
- buji 無事
  Unharmed. That nothing happened with.

Here's the absolute worst way yokatta can be used:

僕　死んでよかったです quote from manga "A Life Without Regrets," Koukai no Nai Jinsei wo 後悔のない人生を

Warning: please don't click the source if you have suicidal tendencies.
(or click it, I'm a caption, not a cop.)
Source: "A Life Without Regrets," Koukai no Nai Jinsei wo 後悔のない人生を, by @avogado6 on Twitter

boku, shinde yokatta desu
僕　死んでよかったです
I'm glad I died.

Okay, that was grim. Let's have a good one instead:

toki ga sugite, ima, kokoro kara ieru
anata ni aete yokatta ne
時が過ぎて　今　心から言える
あなたに会えてよかったね
Time passed, now, I can say from my heart,
I'm glad I met you.
—Anata ni Aete Yokatta あなたに会えてよかった by Koizumi Kyoko 小泉今日子, album Afropia (1991).^{[lyrics from mojim.com, accessed 2019-02-01]}

Regret

Here are some examples of yokatta meaning "I regret not doing this." You'll find yokatta means regret most of the time in manga because manga is full of characters making mistakes and regretting stuff. Literally nobody prepares for future unforeseen circumstances.

Note that "regret" doesn't always mean the speaker made a mistake. That's because:

They can be talking about how things would have been better for you, not for them.
They can be talking about something that's outside of their control.
"Better" doesn't mean the current situation is bad, just that the alternative would have been better.

Manga: Watashi ga Motenai no wa Dou Kangaetemo Omaera ga Warui! 私がモテないのはどう考えてもお前らが悪い！ (chapter 3)

Context: a girl and her friend became high school girls.
zutto chuugakusei no mama nara
yokatta noni na~
ずっと中学生のままなら
よかったのになー
Even though it would have been better if
[we] remained middle school students forever.

Manga: Holy Land (chapter 55)

Context: character regrets his appearance.
bansoukou...
tsuketenai hou ga yokatta na
バンソウコウ･･･
つけてない方がよかったな
It would have been better if if I hadn't put a band-aid.
- Fun fact: band-aid is a brand name, the generic name is "adhesive bandage."
...kami mo kitte-kureba yokatta
･･･髪も切ってくればよかった
...the hair, too, would have been better if I had gone cut it.
- kitte-kureba 切ってくれば
  (ba-form of)
- kitte-kuru 切ってくる
  To cut and come. To go cut and come back.
  (this is kuru 来る in its auxiliary verb usage.)

するんじゃなかった

Note that, sometimes, the phrase janakatta じゃなかった, "was not," the negative past of the da だ copula, can be used to mean you regret doing something too.

In this sense, it means something "wasn't to be" or "wasn't to be done." It shouldn't have been, or shouldn't have been done. For example:

貧乏くさい他人といっしょの列車なんかに乗るんじゃあなかったわ･･･指定席とったって声がつつぬけじゃあない　こんなんだったら居眠りできないけど車でくるんだったわ quote from manga "JoJo's Bizarre Adventure," JoJo no Kimyou na Bouken ジョジョの奇妙な冒険 (chapter 500)

Manga: "JoJo's Bizarre Adventure," JoJo no Kimyou na Bouken ジョジョの奇妙な冒険 (chapter 500)

Context: rich woman boards train.
binbou kusai tanin to
issho no ressha nanka ni
noru-n-jaa nakatta wa...
貧乏くさい他人と
いっしょの列車なんかに
乗るんじゃあ　なかったわ･･･
I shouldn't have boarded a train together
with [all these peasants.]
- binbou kusai tanin 貧乏くさい他人
  People who smell of poverty. (literally.)
- jaa じゃあ
  (in this case, same as ja じゃ, but she pronounces it longer.)
shiteiseki to-ttatte
koe ga tsutsunuke jaa nai
指定席とったって
声がつつぬけじゃあない
Even though you they call it a reserved seat,
you can hear voices through the walls, can't you?
- She's complaining there's nothing special about the seat, since she can hear the peasants talking anyway.
- to-ttatte とったって
  to itta tte と言ったって
  to itta toshite-mo と言ったとしても
  to itte-mo と言っても
  Even if you call it. Even if you say it is.
- tsutsunuke 筒抜け
  To be overheard.
konna-n-dattara
inemuri dekinai kedo
kuruma de kuru-n-datta wa
こんなんだったら
居眠りできないけど
車でくるんだったわ
If it's like this
I wouldn't be able to sleep but
I should have come by car.
- Since janakatta can mean you shouldn't have done something, it makes sense that datta can mean you should have done something.

Note that -n-janakatta ～んじゃなかった is a contraction of -no-dewanakatta ～のではなかった, so that can be used the same way too.

Manga: Houshin Engi 封神演義 (chapter 2)

Context: the battle ends without a fight.
konna koto nara
こんな事なら
If it were to be like this...
go-sen mo hei wo tsurete-kuru no-dewanakatta
５千も兵を連れて来るのではなかった
I shouldn't have brought [all these] 5000 soldiers.
- mo も
  Here, it emphasizes the number 5000. It implies that maybe bringing 100 would suffice, rather than implying he shouldn't have brought any of the 5000.

Yokatta Alone

When yokatta よかった shows up alone, it means either "that's a relief," or "I'm glad," or something along those lines.

Basically, it's the same thing as when yokatta is used after a verb, except this time we don't have the hypothetical "too bad it didn't happen" or "didn't do" case. It's always the "good thing it happened" case.

But that's not to say that yokatta always mean the same thing. This single word have have EXTREMELY HUGE differences in usage.

"I'm Glad"

For example, after offering food or something of the sort to someone, if they don't like it, that would be bad, so, conversely, if they do like it, that "was good," that was a relief, you're glad for that, yokatta.

Manga: Kaguya-sama wa Kokurasetai ~Tensai-Tachi no Ren'ai Zunousen~ かぐや様は告らせたい～天才たちの恋愛頭脳戦～ (chapter 5)

Context: food has been offered.
oishii desu!
おいしーです！
It's delicious!
sou ka
そうか
I see.
yokatta
良かった
I'm glad. (that you liked it.)

"That's a Relief"

Sometimes you think stuff is going to turn bad and it turns out to be good. Clearly, you'd rather say "that's a relief" than "I'm glad" in this case.

Manga: Mob Psycho 100, Mobu Saiko Hyaku モブサイコ１００ (chapter 53)

Context: a woman meets psychics. After confirming they actually have psychic powers:
yokatta...
honmono no kata desu ne...
よかった･･･本物の方ですね･･･
That's a relief... you're real [psychics], aren't you?
- honmono 本物
  Real. Genuine. As opposed to "fake," nisemono 偽物.
- kata 方
  Used to people to people. So "you're people that are real [psychics]."
mae ni intaanetto de
soudan shita toki wa tekitou na
koto iwareta no de...
前にインターネットで
相談した時は適当な
こと言われたので
[It's a relief,] because: when I consulted in the internet before I was told "appropriate" things.
- tekitou 適当
  Appropriate. But often used with a lazy, deceiving nuance. For example, in this case she was told "appropriate" things in the sense they sounded like things a psychic would say (appropriate for a psychic). In other words, they didn't have psychic powers, but they talked as if they were psychics. They were trying to deceive her. And she's relieved to have found real ones this time.

Although "relief" implies the speaker was somehow troubled, this is manga we're talking about, so sometimes the speaker caused the trouble themselves.

Manga: Houshin Engi 封神演義 (chapter 1)

Context: Shinkouhyou blasts Taikoubou with a powerful attack, who retaliates, giving Shinkouyou a little cut in the cheek. Shinkouyou asks his cat to check if Taikoubou survived, and then, after confirming he survived the attack:
yokatta~
よかったー
That's a relief.
ha?
は？
Hah? (the cat doesn't get why he's relieved the guy he was going to kill is still alive.)
watashi wa
umarete gosen'nen
hajimete
jibun no chi wo
mimashita
私は生まれて五千年初めて自分のちを見ました
In the 5000 years I've been born it's the first time I've seen my own blood.
- I think this author likes the number 5000.
Taikoubou... 太公望･･･
watashi wa kare wo
raibaru ni
kettei shimasu
私は彼をライバルに決定します
I've decided he's my rival.

"Thank Goodness"

Finally, there's the yokatta that's so yokatta you can only translate it as "thank God" or "thank goodness" or something similar. This yokatta often accompanies tears.

Manga: Inuyashiki いぬやしき (chapter 15)

yokatta.........
よかった･････････
Thank God.........
poro ポロ
*tear dropping* (mimetic word.)
haa......
はぁ･･････
Ahh......
ureshii...... ureshii......
嬉しい･･････嬉しい･･････
I'm glad..... I'm glad......
- ureshii 嬉しい
  Happy. Glad.

よかったじゃない？

Sometimes, yokatta isn't used to say "I'm glad," but instead to ask people if they're glad. Phrases such as:

yokatta janai? よかったじゃない？
yokatta janai ka? よかったじゃないか？
yokatta janai no? よかったじゃないの？

And other variants mean, literally, "wasn't that good?" Which often translates to asking "shouldn't you be glad that happened?"

Manga: Gintama 銀魂 (chapter 7)

Context: a girl gets a ~~stalker~~ guy who loves her.
yokatta janeeka
よかったじゃねーか
- That was a good thing, wasn't it?
- Shouldn't you be glad?
yome no morai-te ga atte yoo
嫁のもらい手があってよォ
That there's [someone] to take you as a wife.
- morai-te もらい手
  "Taker." From morau もらう, "to take," and the te 手 part means someone who does an action, in this case: taking. (not to be confused with "taking one's hand," that's not a Japanese expression.)