Is my Japanese sentence correct? How to check Japanese grammar without a native speaker

Short answer: there is no single reliable Japanese grammar checker, and the ones that exist catch typos and particle slips rather than the mistakes learners actually make. The five methods below, used together, will tell you whether a sentence is correct — corpus search for whether the phrasing exists at all, a checker for the mechanical errors, and a human or a marking tool for the ones only meaning can settle.

I build BetterLingo from Japan and this is the question I get asked more than any other. It is also the question with the worst available answers: most search results are either "just ask a native speaker" (you do not have one at 11pm) or a spellchecker dressed up as a grammar checker.

Why Japanese grammar checkers are worse than English ones

English grammar checking has decades of tooling behind it and, more importantly, English marks its errors syntactically — a missing article or a broken agreement is visible in the shape of the sentence. A very large share of Japanese learner errors are not like that. Your sentence is grammatical and means the wrong thing.

は vs が — both parse. The choice is about what is old and new information, and the wrong one produces a fully grammatical sentence that lands strangely.
Transitive vs intransitive pairs — 開ける/開く, 落とす/落ちる, 決める/決まる. Both exist, both are correct Japanese, only one says what you meant.
Register — a perfectly formed casual sentence sent to your professor is an error, and no parser will flag it.
Collocation — the grammar is right and Japanese people just do not say it that way. This is the largest category and the one tools help with least.

So "is this correct?" is really three questions: is it well-formed, does it mean what I meant, and would anyone say it. Different methods answer different ones.

Method 1: search the corpus before you trust anything

The single most useful habit: before asking whether your phrasing is correct, find out whether it exists. Put the phrase in quotes into a search engine, or better, use a sentence corpus.

Massif (massif.la) searches real Japanese sentences from published fiction and shows them with context. If your collocation returns nothing there, it is very likely wrong regardless of what any tool says.
Tatoeba has learner-oriented sentence pairs, useful for structure, less reliable for naturalness — many sentences are translated into Japanese.
YouGlish and similar give you spoken usage, which is where register lives.

Corpus search answers "would anyone say it" better than any checker, and it is free. It cannot tell you whether your particular sentence, with your particular subject and object, holds together.

Method 2: run it through a checker for the mechanical errors

Automated checking is genuinely good at a narrow band: typos, kana/kanji conversion mistakes, obvious particle omissions, verb conjugation errors, and mixed politeness levels within one sentence. That band is worth clearing before you show a sentence to anyone, because those errors distract a human reader from the real problem.

Where checkers fail is exactly where learners need them: they will accept 私は先生に本をもらいました and 私は先生に本をあげました equally, though only one of those is a sentence you can say to your teacher without alarm.

BetterLingo's own Japanese grammar checker is free and takes a sentence you wrote; it returns what is wrong and why, rather than only marking it red. Use it — and any other checker — for the mechanical layer, then keep going.

Method 3: back-translate, but do it properly

Machine translation is a bad corrector and a useful detector. Translate your Japanese back into your own language and read the result cold. If it comes back saying something you did not intend, you have found a real problem — that is a true signal.

The reverse is not true. A clean back-translation does not mean the sentence is correct, because translation systems are trained to produce plausible output from imperfect input; they will quietly repair your sentence and hand you the repaired meaning. Treat back-translation as a smoke alarm, never as a certificate.

Method 4: check the three things learners get wrong most

Before you ask anyone, run your sentence past this list. It catches most of what I see:

Every particle: why that one and not the neighbouring one? If you cannot say why it is に and not で, that is the word to check.
Transitivity: who or what is doing this? If the subject did not cause the action, you probably want the intransitive verb, and probably without を.
Tense and aspect: is it ている or た? Japanese ている covers both an ongoing action and a resulting state, and English past tense maps onto both. 結婚しています is "is married", not "is getting married".
Register consistency: pick plain or polite and hold it to the end of the sentence, including inside the subordinate clause if the whole sentence is spoken.

Method 5: get it marked by something that reads meaning

The gap that remains — did this say what I meant — needs something that understands the sentence, not just parses it. Your options are a teacher, a language exchange partner (HelloTalk, italki, Discord servers), Lang-8-style correction communities, or a tool that marks free-form written answers and explains the correction.

Human correction is the gold standard and it is slow — expect hours to days, and expect corrections without explanations, because native speakers know what is right far more reliably than they know why. Tools are instant and less trustworthy on nuance. In practice: use a tool for the loop you run twenty times a night, and save your human for the sentences that matter.

The workflow that actually works

Write the sentence.
Self-check the four points in method 4 — particle, transitivity, aspect, register.
Corpus-search anything you are unsure exists.
Run it through a checker for the mechanical layer.
Back-translate as a smoke alarm.
Send the ones that still matter to a human.

Steps 2 to 5 take under a minute once the habit is in, and they are what turns "is this right?" from a question you ask into a question you can mostly answer.

Related reading: Japanese particle practice for the particle half of this, and causative vs causative passive for one of the forms this checklist catches most often.

Next steps

Take a sentence you wrote this week and run it through the six steps above. If you want the mechanical pass done for you, the grammar checker is free and needs no account.