Examples

C# example: quick start in 2 minutes

2026-01-24

This snippet demonstrates how to solve a text captcha using C# and HttpClient.

Complete Code Snippet

Copy and paste this into your console application:

Console Application

using System;
using System.IO;
using System.Net.Http;
using System.Text.Json;
using System.Threading.Tasks;

class Program
{
    static async Task Main()
    {
        const string apiKey = "YOUR_API_KEY";
        const string imagePath = "captcha.png";
        
        using var client = new HttpClient();
        client.DefaultRequestHeaders.Add("X-API-Key", apiKey);
        
        // Prepare multipart form data
        await using var stream = File.OpenRead(imagePath);
        var content = new MultipartFormDataContent();
        content.Add(new StreamContent(stream), "image", Path.GetFileName(imagePath));
        
        // Send request to API
        var response = await client.PostAsync(
            "http://api.noncaptcha.com/api/json/text",
            content
        );
        
        // Read and parse result
        var jsonResponse = await response.Content.ReadAsStringAsync();
        
        Console.WriteLine($"Status: {response.StatusCode}");
        Console.WriteLine($"Response: {jsonResponse}");
        
        if (response.IsSuccessStatusCode)
        {
            var result = JsonSerializer.Deserialize<TextResponse>(jsonResponse);
            Console.WriteLine($"Solved text: {result?.text}");
        }
    }
    
    // Response model
    public class TextResponse
    {
        public string text { get; set; }
    }
}

Response Parsing

The API returns a simple JSON object:

JSON Response

{
  "text": "abc123"
}

You can use System.Text.Json to deserialize it into a strongly typed object.

Async/Await Pattern

Modern C# approach with proper async handling:

Modern Async Pattern

public class CaptchaSolver
{
    private readonly HttpClient _client;
    private readonly string _apiKey;
    
    public CaptchaSolver(string apiKey)
    {
        _apiKey = apiKey;
        _client = new HttpClient
        {
            BaseAddress = new Uri("http://api.noncaptcha.com"),
            Timeout = TimeSpan.FromSeconds(30)
        };
        _client.DefaultRequestHeaders.Add("X-API-Key", apiKey);
    }
    
    public async Task<string> SolveTextCaptchaAsync(string imagePath)
    {
        using var stream = File.OpenRead(imagePath);
        var content = new MultipartFormDataContent();
        content.Add(new StreamContent(stream), "image", Path.GetFileName(imagePath));
        
        var response = await _client.PostAsync("/api/json/text", content);
        
        if (!response.IsSuccessStatusCode)
        {
            throw new Exception($"API error: {response.StatusCode}");
        }
        
        var json = await response.Content.ReadAsStringAsync();
        using var doc = JsonDocument.Parse(json);
        return doc.RootElement.GetProperty("text").GetString();
    }
    
    public void Dispose() => _client.Dispose();
}

// Usage
using var solver = new CaptchaSolver("YOUR_API_KEY");
var result = await solver.SolveTextCaptchaAsync("captcha.png");
Console.WriteLine($"Result: {result}");

Error Handling

Complete example with error handling:

With Error Handling

try
{
    using var client = new HttpClient();
    client.DefaultRequestHeaders.Add("X-API-Key", "YOUR_API_KEY");
    
    using var stream = File.OpenRead("captcha.png");
    var content = new MultipartFormDataContent();
    content.Add(new StreamContent(stream), "image", "captcha.png");
    
    var response = await client.PostAsync(
        "http://api.noncaptcha.com/api/json/text",
        content
    );
    
    var result = await response.Content.ReadAsStringAsync();
    
    if (response.StatusCode == System.Net.HttpStatusCode.PaymentRequired)
    {
        Console.WriteLine("❌ Insufficient balance!");
        return;
    }
    
    if (!response.IsSuccessStatusCode)
    {
        Console.WriteLine($"❌ API Error: {response.StatusCode}");
        Console.WriteLine($"Response: {result}");
        return;
    }
    
    // Parse JSON response
    using var doc = JsonDocument.Parse(result);
    var text = doc.RootElement.GetProperty("text").GetString();
    
    Console.WriteLine($"✅ Solved: {text}");
}
catch (FileNotFoundException)
{
    Console.WriteLine("❌ Captcha file not found!");
}
catch (HttpRequestException ex)
{
    Console.WriteLine($"❌ Network error: {ex.Message}");
}
catch (JsonException ex)
{
    Console.WriteLine($"❌ Invalid JSON response: {ex.Message}");
}
catch (Exception ex)
{
    Console.WriteLine($"❌ Unexpected error: {ex.Message}");
}

Tip: For production code, consider using a reusable HttpClient instance and proper dependency injection.