1 Best APIs for Custom rules in Nigeria

LanguageTool API is an open-source grammar, spelling, and style checker that supports over 30 languages, offering automated proofreading capabilities for writing tools, content management systems, and educational platforms. Unlike basic spell checkers that only catch misspelled words, LanguageTool performs grammatical analysis to identify agreement errors, incorrect tense usage, punctuation mistakes, style issues, and awkward phrasing that basic spell-check misses. The check endpoint accepts a text string and language code and returns a list of detected issues, each with the matched text span, offset position in the input, error type, human-readable message explaining the issue, a list of suggested replacements, and a rule identifier. Applications can use the offset and length data to highlight specific errors in a text editor interface and present replacement options inline. The rule identifier allows developers to map errors to documentation or learning resources explaining why the flagged usage is incorrect. Grammar rule coverage goes beyond simple subject-verb agreement. LanguageTool detects complex errors including confusing commonly mixed word pairs (affect/effect, their/there/they're), redundant phrases (added bonus, completely unique), incorrect article usage (a vs. an), comma splices, dangling modifiers, and informal language use in contexts requiring formal register. For Nigerian English users who may apply Nigerian English conventions in contexts requiring standard British or American English, LanguageTool's style suggestions help align writing with international formal writing standards. The language detection feature automatically identifies the language of input text, routing it to the appropriate grammar engine without requiring the developer or user to specify a language code. For Nigerian applications serving users who switch between English and French (particularly relevant for businesses operating across Nigeria's border with Francophone West Africa), automatic language detection ensures each user's text is checked against the right grammar rules. Custom dictionary integration allows applications to add organization-specific terminology — brand names, product names, industry jargon — to LanguageTool's allowed words list, preventing false positives where correctly spelled company-specific terms are flagged as errors. Nigerian tech companies, media organizations, and professional services firms can configure custom dictionaries that include Nigerian proper nouns and industry-specific terms. LanguageTool's picky mode is a stricter checking level that flags additional style issues beyond standard grammar errors — overly long sentences, passive voice overuse, redundant phrases, and informal register in formal contexts. For Nigerian professional writing tools targeting business communication, legal documents, or academic papers, picky mode helps users elevate their writing to match the formal register expected in high-stakes professional contexts. Nigerian law firms, consulting firms, and academic institutions that want to maintain consistent written standards across their communications benefit from the elevated scrutiny of picky mode checking. The API also provides a Sentence Boundaries Detection feature that correctly identifies where one sentence ends and another begins even in complex texts with abbreviations, decimal numbers, and quoted speech. For Nigerian text processing pipelines that feed into sentence-level analysis tools (sentiment analysis, readability scoring, text classification), accurate sentence boundary detection is a critical preprocessing step that affects downstream analysis quality.