たことがある details

write + (past) + have done before

kaita koto ga aru

have done before; have the experience of doing

meaning: have written before

ねえ、ウミガメって見みたことある？

nee, umigame tte mita koto aru?

Hey, have you ever seen a sea turtle? casual

京都きょうとには行っいったことがある。

kyouto ni wa itta koto ga aru.

I have visited Kyoto before. neutral

Examples

have done before — an experience located somewhere in one's past, at least once

ねえ、ウミガメって見みたことある？

nee, umigame tte mita koto aru?

Hey, have you ever seen a sea turtle? casual

京都きょうとには行いったことがある。

kyouto ni wa ittakotogaaru.

I have visited Kyoto before. neutral

実じつは、通訳つうやくの仕事しごとをしたことがあります。

jitsu wa, tsuuyaku no shigoto o shitakotogaarimasu.

Actually, I have worked as an interpreter before. neutral

Reports experience, not news — a specific recent event takes the plain past: ×昨日すしを食べたことがある, just 食べた. Casual speech drops が: 見たことある？

たばかりだ
Both stamp a finished event onto the present off the た-form, but たことがある files it as experience from anywhere in one's past (十年前に行ったことがある is fine), while たばかり claims the event as fresh — swap them and "I've been there before" becomes "I just went".

ことがある
One tense apart, opposite time claims — 行ったことがある reports past experience ("have been, at least once"), 行くことがある reports occasional occurrence ("sometimes go"); dropping the た at reading speed turns a biography into a habit.

Pattern	Attaches to
ことがある