A calm grammar tool, not another red-line factory.

The grammar checking core is powered by Harper, an open-source English grammar engine written in Rust. Harper runs as a WebAssembly (WASM) module compiled directly into your browser tab, which is why the checker starts in under two seconds and works without a server connection. When you paste or type a sentence, the engine runs locally on your device and the flagged issues appear without any network round-trip.

Most grammar checkers work by sending every keystroke to a cloud server, running checks centrally, and streaming suggestions back to your screen. That architecture is functional but introduces latency, requires a constant connection, and creates a log of your writing on someone else's infrastructure. Grammarlyzer inverts that model: the engine lives inside the browser tab and checks text in under 50 milliseconds on most modern devices. Nothing about your draft leaves your machine for the routine grammar check.

AI Polish is architecturally separate from the local checker. When you press the Polish button, a snapshot of your current draft travels to an AI rewriting service, and the rewritten version returns. This is an explicit action you initiate — not a background process running quietly while you type. The request is not used to retrain models on your private text, and sign-in is required only at the moment the Polish button is pressed, never earlier. The distinction between the local grammar engine and the optional AI rewrite is a core design decision, not a marketing claim.

Every grammar guide on Grammarlyzer starts from a real writing problem: a confused word pair that trips up careful writers, a punctuation rule people apply inconsistently, a structural pattern that makes sentences harder to follow. Topics are chosen based on what causes repeated confusion in emails, academic writing, and professional documents — not what fills a chapter in a traditional grammar textbook.

Each guide is written to answer the specific question a writer faces at the keyboard. For a confused-word page like affect vs. effect, that means showing the decision rule, a quick test the writer can apply without memorizing linguistic categories, the most common mistake with a workplace or school example, and the edge cases where the rule gets more complicated. For a punctuation guide like comma usage before a conjunction, it means explaining each pattern with the sentence type that requires it, rather than listing seven abstract principles and leaving the application to the reader.

Guides are reviewed against their own examples, not just edited for tone. If an example uses a rule inconsistently, the example is rewritten. If an explanation could be read two ways, the explanation changes. If a common exception is missing, a section is added. The standard is whether a writer who is actively revising a real document would leave the page knowing what to do differently the next time they face that grammar decision.

The Learn section covers more than 100 grammar topics organized by category: confused word pairs, punctuation rules, sentence structure, verb tenses, modal verbs, pronoun usage, and vocabulary for specific writing contexts like academic papers and business emails. Topics that share conceptual territory are linked together so a writer who arrives with one question can find related guidance without starting a new search.

The checker catches common mechanical errors reliably: misspellings, subject-verb agreement failures, doubled words, confused word pairs in the Harper rule set, spacing problems around punctuation, and apostrophe errors. For these categories, the correction is usually straightforward and the reason can be stated clearly. The checker is genuinely useful as a first-pass review of a draft before it goes to another reader.

The checker is not a substitute for a professional copy editor, a legal reviewer, a writing instructor, or an academic tutor. For context-dependent questions — whether passive voice serves a particular sentence better than active, which citation format an institution requires, whether a legal disclaimer needs rewording for a specific jurisdiction, whether a sentence's tone is right for its audience — the checker is a starting point, not the final word. These are judgment calls that depend on knowledge the checker does not have.

Grammar guides on Grammarlyzer reflect standard edited American English as documented in major usage references. When a rule is genuinely contested among careful writers, the guide says so. When two forms are correct in different contexts, the guide explains the context rather than declaring one form wrong. Grammar is descriptive before it is prescriptive, and guides that pretend otherwise train writers to apply rules incorrectly to sentences where the stricter form is not required.

If you find an error in a guide — a wrong example, an overclaim, a missing exception, a broken link — use the contact page to report it. We update and correct pages when the issue is clearly identified. The standard for a published guide is whether it would help a real writer make a better decision on a real document, not whether it sounds authoritative in isolation.

Grammar guides on Grammarlyzer are written and reviewed by an editorial team with backgrounds in English language instruction, professional editing, and applied linguistics. Every guide goes through at least two review passes: a content pass that checks the rule, examples, and edge cases against major usage references, and a structural pass that ensures the page answers the stated question directly and completely.

Primary references include The Chicago Manual of Style (17th ed.), Garner's Modern English Usage (4th ed.), the AP Stylebook, and Merriam-Webster's Dictionary of English Usage. For contested usage questions — cases where style guides disagree or where conventions differ by register, dialect, or discipline — the guide identifies the disagreement and explains the context rather than declaring one form universally correct.

The grammar checking engine (Harper, open-source) catches mechanical errors reliably. The learning guides address the reasoning behind the rules — why a correction works, when exceptions apply, and how context changes the right answer. This combination is why the checker and the Learn section are paired: the tool flags the issue; the guide explains it.

Our guides are written and reviewed by human editors. We do not auto-generate published article content with AI writing tools and post it unreviewed; AI may assist with drafting or research, but a person checks and approves every guide. Full details are in our editorial policy.