In short

Japanese has a huge, everyday layer of sound-and-manner words - ざあざあ (zāzā, pouring rain), きらきら (kirakira, twinkling), どきどき (dokidoki, heart pounding) - and adults use them constantly, in the news as well as in manga. They are a grammar topic because each one enters the sentence through a fixed slot: as an adverb with optional と, or with する, or with だ／の. Learn each word together with its slot (ざあざあ降る, お腹がぺこぺこです) and you will never have to guess.

The rule

Step 1 - Three families: sound, appearance, feeling.

• 擬音語 giongo - a real noise you could record: ワンワン wanwan (a dog barking), ガタガタ gatagata (rattling), ザーザー zāzā (heavy rain). (Strictly, a voice - ワンワン - is 擬声語 giseigo and 擬音語 is the non-living noise, but everyday usage lets 擬音語 cover both.)
• 擬態語 gitaigo - manner and appearance, with no sound at all: きらきら kirakira (sparkling), ゆっくり yukkuri (slowly), にこにこ nikoniko (smiling). English has almost nothing like this, which is why these are the hard ones.
• 擬情語 gijōgo - what is happening inside a person: どきどき dokidoki (heart racing), いらいら iraira (irritated), わくわく wakuwaku (thrilled).

Step 2 - Recognize the four shapes.

Most of these words are built to a small number of moulds, and the mould predicts the meaning-type as well as the grammar (see the tables below): reduplication (ぺらぺら) for something repeated or continuous, root + っと (さっと) for one quick action, root + り (ゆっくり) for something unhurried and spread out, and root + ん／long vowel (ばたん, ドーン) for a single burst.

Step 3 - Sound symbolism: the consonant and the vowel carry meaning.

This is the part that lets you guess a word you have never met. A voiced initial (the dot: が, ざ, だ, ば) makes the thing bigger, heavier, coarser or less pleasant than its voiceless twin: ころころ korokoro is a small ball rolling, ごろごろ gorogoro is a boulder rolling (or a person lazing about). The p- row (ぱ, ぴ) is light, crisp and bouncy. Small vowels, especially い, feel small, thin and sharp; お and あ feel big and open.

Step 4 - Slot A: the adverb, with optional と.

The default use is as a manner adverb in front of the verb: 雨がざあざあ降ります (ame ga zāzā furimasu, it rains heavily). Many of them can take と, and whether と is optional, obligatory or impossible depends on the shape:

• Reduplicated forms - と is optional and usually dropped in speech: きらきら（と）光る.
• Forms ending in り - と is optional, and adding it sounds a shade more deliberate or literary: ゆっくり（と）歩く.
• Forms ending in っ - と is part of the word and cannot be dropped: さっと, ちらっと, じっと, ぱっと. There is no ×ちらっ見る.
• Before する: the reduplicated words insert no と - どきどきします, not ×どきどきとします. The り-shaped words keep と optional here too, and it is common in writing: はっきり（と）する, ゆっくり（と）した. The っと／ん class, by contrast, carries its と in, because that と is part of the word: ほっとする, ぞっとする, しーんとする. Before です／だ, と never appears.

Step 5 - Slot B: + する, for states and feelings.

Add する and the word becomes a verb meaning “be in that state / feel that way”: びっくりする bikkuri suru (be startled), どきどきする, のんびりする nonbiri suru (take it easy), ざらざらする zarazara suru (feel rough). For an ongoing state use 〜している (lesson 15): この紙はざらざらしています. To modify a noun, this group uses 〜した, not な: きらきらした目 kirakira shita me (sparkling eyes).

Step 6 - Slot C: + だ／です and + の, for predicates and modifiers.

A second group behaves like a noun or な-adjective instead: it predicates with です／だ and modifies with の (several also allow な: ぼろぼろな服). お腹がぺこぺこです (onaka ga pekopeko desu, I’m starving), 英語がぺらぺらです (eigo ga perapera desu, fluent in English), ぼろぼろの服 boroboro no fuku (worn-out clothes), へとへとです hetoheto desu (worn out). Which group a word belongs to is lexical - learn it with the word, exactly as you learn a verb’s transitivity partner.

Step 7 - Slot D: sounds take 言う and 音がする.

For actual noises the standard partners are 〜（と）言う and 〜（と）音がする: ドアがガタガタ言っています (doa ga gatagata itte imasu, the door is rattling), 隣からガタガタと音がします (tonari kara gatagata to oto ga shimasu). With a person, 〜言う means grumbling: ぶつぶつ言う butsubutsu iu (mutter, complain under one’s breath).

Step 8 - Orthography. The convention is katakana for 擬音語 (real sounds: ワンワン, ガタガタ, ザーザー) and hiragana for 擬態語・擬情語 (きらきら, ゆっくり, どきどき). It is a tendency, not a law: hiragana softens a sound word (ざあざあ), and katakana on a mimetic word makes it loud or stylized, which is why manga uses katakana everywhere.

Forms & patterns

The four shapes:

Sound symbolism - the same root, voiced and voiceless:

The syntactic slots:

A high-frequency starter set, by domain:

Examples

Common mistakes

• きらきらな目 (kirakira na me) -> きらきらした目 (kirakira shita me) - a する-type mimetic like きらきら modifies a noun with した, not with な. It is not a な-adjective, however much it looks like one.
• さっ立ち上がりました。 (Sa’ tachiagarimashita.) -> さっと立ち上がりました。 (Satto tachiagarimashita.) - in the っと class the と is part of the word; dropping it leaves a non-word. Same for ちらっと, ぱっと, じっと.
• お腹がぺこぺこしています。 (Onaka ga pekopeko shite imasu.) -> お腹がぺこぺこです。 (Onaka ga pekopeko desu.) - for hunger, ぺこぺこ is a です／だ word. ぺこぺこする does exist, but it means bow and scrape, grovel - so the する version says something quite different. The slot is lexical, so memorize it with the word.
• 雨がざあざあです。 (Ame ga zāzā desu.) -> 雨がざあざあ降っています。 (Ame ga zāzā futte imasu.) - a 擬音語 is an adverb: it needs its verb. Sound words almost never stand as the predicate.
• 彼は日本語をぺらぺらです。 (Kare wa Nihongo o perapera desu.) -> 彼は日本語がぺらぺらです。 (Kare wa Nihongo ga perapera desu.) - ぺらぺらだ is a state, not an action, so the language is marked with が, exactly as with 上手だ and 好きだ.

Tips

• The dot makes it heavier. Whenever you meet an unknown word starting with が／ざ／だ／ば, look for the voiceless twin you already know and shift the picture one size up and one shade rougher: さらさら -> ざらざら, とんとん -> どんどん. This single rule unlocks hundreds of pairs.
• Japanese even has a word for silence. しーんとする (shīn to suru) describes a room going completely quiet: 教室がしーんとしました (kyōshitsu ga shīn to shimashita, the classroom fell silent). That is the clearest proof that 擬態語 are not “sound effects” in the English sense - they paint appearance, atmosphere and feeling, not noise.
• Learn the chunk, not the word. Dictionaries handle these badly, often giving only a vague gloss and no slot. So store them as collocations: ざあざあ降る, ぐっすり寝る, お腹がぺこぺこだ, びっくりする, ぼろぼろの服. Manga, anime and drama are the natural harvesting ground - just remember that manga’s oversized katakana effects are stylized, while the words above are ordinary adult speech.
• ゆっくりする is a false friend. It does not mean “do it slowly”; it means take your time, relax: どうぞゆっくりしてください (dōzo yukkuri shite kudasai, please make yourself at home). For “walk slowly” you need the adverb slot: ゆっくり歩いてください.