Grammar Check

Discover how to seamlessly incorporate AI-powered grammar checking into TX Text Control .NET for Windows Forms by leveraging a local large language model. Identify grammatical errors, enhance sentence structure, and suggest contextual writing improvements directly in the document editor. Avoid sending sensitive documents to external services.

Beyond Traditional Spell Checking

Spell checking has been a standard feature of word processing applications for decades. Traditional spell checkers compare words against dictionaries to identify unknown terms and suggest corrections. While this approach is effective for identifying typographical errors, it is limited in its ability to evaluate grammar, sentence structure, and the meaning of written content.

Consider the following sentence:

"The customer have received the documents yesterday and is waiting for an answer."

Although every word is spelled correctly, the sentence contains a grammatical error. A dictionary-based spell checker might not catch the error because it does not analyze the relationship between words or understand the sentence's grammatical context. This is where artificial intelligence offers a different approach.

Large language models (LLMs) analyze complete sentences and paragraphs, not just individual words. They can evaluate grammatical relationships, recognize problems with verb agreement and tense, and suggest corrections that preserve the intended meaning. Depending on the model and instructions, LLMs can also identify awkward phrasing, punctuation errors, and inconsistencies in writing style.

By combining TX Text Control's document editing capabilities with AI-based language analysis, developers can enhance their Windows Forms applications with contextual grammar checking that goes beyond traditional spell checking.

Bringing AI Grammar Checking Directly into the Editor

In our previous article, Adding an AI Sidebar to TX Text Control .NET for Windows Forms , we introduced a reusable component that connects AI functionality to an existing TX Text Control editor. This sample offers several writing tools, such as text summarization, translation, rephrasing, and AI-powered grammar checking. Instead of requiring users to copy document content into an external AI application, these capabilities are integrated directly into the editing experience.

Add AI writing tools to TX Text Control Windows Forms with a reusable sidebar component. Summarize, rephrase, translate, and review grammar in the editor. Clone the sample, download the Qwen3.5-4B GGUF model from Hugging Face, and connect it through the built-in settings dialog.

Adding an AI Sidebar to TX Text Control .NET for Windows Forms

This integration is particularly useful for grammar checking because it displays corrections exactly where errors occur. When the AI identifies a potential problem, it marks the corresponding text with a blue, wavy underline.

Users can then inspect the error, review the suggested correction, and decide whether to apply or ignore it. This familiar interaction makes AI-based grammar checking feel like a natural extension of the word processor rather than a separate service.

It's important to note that while AI analyzes the text, TX Text Control remains responsible for document editing, formatting, and applying corrections.

How AI Grammar Checking Works

Unlike conventional grammar engines, which rely on predefined linguistic rules, large language models can evaluate sentences in their broader contexts.

Consider the following sentence, for example:

The AI recognizes that "results" is the grammatical subject, so it requires the plural verb form. Instead of simply replacing a word, it can also provide an explanation of the issue.

This is especially useful when sentences are complex, contain subordinate clauses, or depend on context from previous sentences.

A grammar checker powered by AI can identify several types of errors, such as subject-verb agreement, incorrect verb tenses, missing articles, punctuation errors, unusual word order, and grammatical inconsistencies. However, because language models are probabilistic, their findings are suggestions rather than guaranteed corrections. A well-designed application should always allow users to make the final decision.

Continuous Grammar Checking While Typing

One interesting feature of the Windows Forms AI Sidebar sample is its ability to perform grammar checks in the background. Users do not need to send every sentence to the AI explicitly. Instead, the component analyzes text after the user pauses typing and displays the results directly in the document.

This implementation follows a workflow designed to avoid interrupting the writing process.

The user writes a sentence. The editor continues to behave as a normal TX Text Control word processor.

The application identifies text for analysis. After a pause, the background grammar checker submits the relevant sentence to the configured AI model.

The AI evaluates the text. The model returns findings and proposed corrections based on the grammatical context.

Potential errors are highlighted. Blue, wavy underlines indicate suggestions without automatically modifying the document.

The user reviews a correction. The suggested replacement can be applied or ignored directly in the editing interface.

The sample also provides an optional idle-checking mechanism. After five seconds of inactivity, it gradually analyzes additional sentences. This allows users to receive feedback on existing document content without initiating a full manual review.

An important feature of this implementation is that previous findings remain visible as users continue writing in other sections of the document. The background AI analysis assists the author without constantly interrupting or distracting from the writing process.

Both grammar checking and typing suggestions can be enabled or disabled in the component's settings.

Using a Local LLM for Private Grammar Checking

Grammar checking is an interesting application of local AI because many business documents contain information that should not be shared outside the user's environment.

Customer correspondence, internal reports, legal documents, and healthcare-related content often contain confidential information. Sending entire sections of documents to an external AI service raises privacy, compliance, and data governance concerns.

The Windows Forms AI Sidebar supports local inference using GGUF language models. In this example, we use Qwen3.5-4B, a compact language model that can run locally with a compatible inference runtime.

With local inference, the grammar checker sends relevant text to a model on the user's workstation instead of to a public API. Once the model and inference runtime are available locally, grammar checks can be performed without an external model service.

Alternatively, the application can connect to an OpenAI-compatible endpoint if an organization prefers a centrally managed AI infrastructure.

This deployment flexibility is especially important for enterprise software. Developers can integrate AI into existing applications and decide where document content is processed and which models are used.

Integrating Grammar Checking into an Existing Windows Forms Application

The AI Sidebar is available as a reusable source code project on GitHub:

Windows Forms AI Sidebar Sample

Get the reusable AISidebar project and the complete Windows Forms sample. Connect AiAssistant to an existing TextControl to add writing actions, selection tools, typing suggestions, and grammar feedback.

https://github.com/TextControl/Windows.Forms.AI.Sidebar

The component is designed to minimize the integration effort. After adding the AISidebar project to your solution, you can place the AiAssistant component on a Windows Form and connect it to an existing TextControl instance.

Alternatively, the integration can be created programmatically:

using TXTextControl;

components ??= new System.ComponentModel.Container();

var assistant = new AiAssistant(components) { TextControl = textControl1 }; The component uses the native TX Text Control sidebar to create its own user interface. It also manages its AI connection and associated inference resources.

The sample communicates with the configured language model using the TXTextControl.AI NuGet package. This separates the model integration from the document processing functionality.

After connecting a local GGUF model or a supported remote endpoint in Settings , developers can enable and test background grammar checking with representative document content.

For detailed setup instructions, including how to download the Qwen model and configure the inference runtime, refer to the original AI Sidebar tutorial .

Why Grammar Suggestions Should Be Reviewable

Although AI can generate convincing corrections, it does not always understand the intended meaning of a sentence. In technical, legal, or medical documents, a minor change in wording can alter the meaning of an important statement. For this reason, an AI grammar checker should not rewrite document content automatically without user interaction.

The Windows Forms sample uses a review-based approach. AI findings are displayed as annotations, and proposed corrections are only applied when the user explicitly accepts them.

When a correction is accepted, the component uses the TX Text Control editing API to replace the relevant text with a native undo action. This enables the user to undo the change using the editor's standard Undo feature.

The integration also checks the captured source text before applying a generated replacement. This helps prevent stale suggestions from overwriting text that has changed since the AI request was initiated.

The separation of AI analysis from deterministic document operations is an important architectural principle. While the language model generates a suggestion, the document editor is responsible for modifying the actual document.

Traditional Spell Checking and AI Grammar Checking Complement Each Other

AI-based grammar checking does not replace traditional spell checking.

Conventional spell checkers remain useful for detecting typographical errors, validating words against domain-specific dictionaries, and providing predictable results with minimal latency. However, AI adds contextual language analysis and can suggest improvements that dictionary-based systems cannot easily determine.

Traditional spell checking AI grammar checking Dictionary-based word validation Contextual sentence analysis Detects unknown or misspelled words Detects grammatical and phrasing problems Fast, predictable response Model-dependent response time Supports specialized dictionaries Can consider surrounding language context Usually deterministic Suggestions may vary between requests

Combining these two approaches creates an effective writing environment. Traditional spell checking handles immediate word-level validation, and AI evaluates grammar and writing quality in the background.

For interactive desktop applications, response times are important to consider. Model performance depends on the hardware used, the selected inference backend, and the size of the text being analyzed. Sending shorter sentences rather than entire documents can help maintain the responsiveness of background checks.

Extending Grammar Checking to Enterprise Applications

The grammar-checking sample is not limited to general-purpose word processing. Since the component is available as source code, developers can adapt its prompts and validation workflow to their business's specific requirements.

For example, a legal document editor could prioritize grammatical correctness while preserving defined terms and contractual language. A medical application could instruct the model to avoid altering clinical terminology. A customer service application, on the other hand, could evaluate professional tone and clarity alongside grammar.

While these instructions can improve the relevance of suggestions, they do not guarantee that the AI will always respect terminology or preserve meaning. For applications requiring strict compliance, deterministic validation and human review should remain part of the workflow.

This is one advantage of integrating AI into an established document component. Developers can combine model-based analysis with application-specific business rules, user permissions, document structures, and existing editing workflows.

The result is more than just an AI text box added to an application. Rather, it is an integrated writing assistant that operates within the context of a professional document editor.

Conclusion

AI-powered grammar checking shows how modern language models can benefit existing desktop applications without replacing their established document editing infrastructure.

With TX Text Control .NET for Windows Forms, developers can integrate contextual grammar analysis and display suggestions directly in the document. Users can then review and apply corrections through familiar editing interactions.

The ability to run a local large language model (LLM) makes this approach particularly interesting for enterprise applications that process confidential information and require control over their AI infrastructure.

We combine reliable, deterministic document technology with the language understanding capabilities of AI. TX Text Control handles documents and editing operations while the language model provides contextual intelligence.

Featured Product

AI Development

Text Control MCP Server

Text Control Agent Skills

Server and Web Document Processing

TX Text Control .NET Server

Client-Side Packages - works together for web apps

DS Server

ReportingCloud

Desktop Document Processing

Windows Forms

TX Text Control .NET

TX Spell .NET

WPF

TX Text Control .NET

TX Spell .NET

ActiveX

TX Text Control ActiveX

Featured Projects

SignFabric

AI-Powered Documents

HEDBridge

Core Technologies

​

Latest Posts

​

Support

Getting Started

​

Other Resources

Company

Contact

Newsletter

Legal

Text Control Account

​

​

Grammar Check

Post tagged with Grammar Check in 2026 ​

October 2026

Post tagged with Grammar Check in 2026