CapSkip .NET SDK — Captcha Solver for C# and .NET

Solve reCAPTCHA v2, reCAPTCHA v3, Cloudflare Turnstile, GeeTest, ALTCHA, Capy Puzzle, CaptchaFox, Friendly Captcha and image captchas from C#.

Official .NET client for CapSkip, a local captcha solver that runs on your own machine. Licensed once, not billed per solve.

dotnet add package CapSkip

Targets .NET Standard 2.0, so it runs on .NET 6/7/8/9+, .NET Core 2.0+, and .NET Framework 4.6.1+.

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How it works

CapSkip is a desktop app. It does the solving on your machine and exposes the standard captcha-solver HTTP API — the same in.php / res.php endpoints every 2captcha-compatible client already speaks — on 127.0.0.1:8080.

This SDK is a thin wrapper over that API, with the method names you would expect: NormalAsync(), RecaptchaAsync(), TurnstileAsync(), GeetestAsync(), AltchaAsync(), CapyAsync(), CaptchaFoxAsync(), FriendlyCaptchaAsync(). Nothing leaves your network, and there is no credit balance to keep an eye on.

Supported captcha types

Captcha	Method
Image captcha solver (distorted text / OCR)	solver.NormalAsync(file)
reCAPTCHA v2 solver (checkbox)	solver.RecaptchaAsync(sitekey, url)
reCAPTCHA v2 invisible solver	RecaptchaAsync(sitekey, url, new() { ["invisible"] = 1 })
reCAPTCHA Enterprise solver	RecaptchaAsync(sitekey, url, new() { ["enterprise"] = 1 })
reCAPTCHA v3 solver	RecaptchaAsync(sitekey, url, new() { ["version"] = "v3", ["action"] = "submit" })
reCAPTCHA v3 Enterprise	RecaptchaAsync(sitekey, url, new() { ["version"] = "v3", ["enterprise"] = 1 })
Cloudflare Turnstile solver (widget)	solver.TurnstileAsync(sitekey, url)
Cloudflare Turnstile (challenge page)	TurnstileAsync(sitekey, url, new() { ["data"] = ..., ["pagedata"] = ... })
GeeTest v3 solver (slide puzzle)	solver.GeetestAsync(gt, challenge, url)
ALTCHA solver (proof-of-work)	solver.AltchaAsync(url, options)
Capy Puzzle solver (slide puzzle)	solver.CapyAsync(sitekey, url)
CaptchaFox solver (widget)	solver.CaptchaFoxAsync(sitekey, url)
Friendly Captcha solver (proof-of-work)	FriendlyCaptchaAsync(sitekey, url, new() { ["version"] = "v2" })

The options argument is a Dictionary<string, object?> — the table shortens it to new() { ... } to stay readable; full signatures are in the API Reference.

hCaptcha and FunCaptcha/Arkose are not supported. hCaptcha is the one people misidentify most often, since it also puts a data-sitekey on the widget — check for class="h-captcha" or a js.hcaptcha.com script before reaching for RecaptchaAsync().

Point the SDK at the live captcha demo pages to sanity-check your setup against real widgets.

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Quick start (5 minutes)

1. Install the CapSkip captcha solver

Download and run the CapSkip desktop app — CapSkipInstaller.msi. Leave it running in the background.

In CapSkip settings, note:

• API port (default: 8080)
• API key (optional — if validation is disabled, any string works)

2. Install the SDK

dotnet add package CapSkip

3. Solve your first captcha

using CapSkip;

var solver = new CapSkipClient(host: "127.0.0.1", port: 8080);

var result = await solver.RecaptchaAsync(
    "YOUR_SITEKEY",
    "https://example.com/page-with-recaptcha");

Console.WriteLine(result.Code); // g-recaptcha-response token

Prerequisite: CapSkip must be running before you call the SDK. If you see a connection error, see Troubleshooting.

Every solve method is asynchronous — await it (or call .GetAwaiter().GetResult() from synchronous code).

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Why solve captchas locally

Cloud captcha APIs charge per solve, which turns a retry loop into an expense and routes every page URL and sitekey you touch through someone else's queue.

CapSkip flips that around:

• Unlimited solving — one license, no per-captcha charge, no balance to top up
• Runs on 127.0.0.1 — the SDK never talks to a third-party server
• No per-key rate limit — throughput is whatever your machine can manage
• Fast — image captchas come back in well under a second; a typical reCAPTCHA v2 lands in 30–45 seconds

Coming from 2captcha or Anti-Captcha

CapSkip answers on the same in.php / res.php endpoints, so it works as a 2captcha API alternative: an existing integration usually needs nothing more than its host pointed at 127.0.0.1:8080. The migration notes cover the details, if you would rather keep your current client library than switch to this one.

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Documentation

Guide	Description
Tutorial	Complete walkthrough of every captcha type
Getting Started	Full setup: CapSkip app, SDK install, first program
API Reference	All classes, methods, parameters, and return values
Examples	Ready-to-run samples for every captcha type
Troubleshooting	Connection errors, timeouts, proxy issues
Contributing	Development setup, tests, pull requests
Changelog	Release history

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Configuration

using CapSkip;

var solver = new CapSkipClient(
    apiKey: "capskip",        // your CapSkip API key (or any string if validation is off)
    host: "127.0.0.1",        // CapSkip host
    port: 8080,               // CapSkip port from app settings
    defaultTimeout: 120,      // seconds — image captcha polling timeout
    recaptchaTimeout: 300,    // seconds — reCAPTCHA / Turnstile / GeeTest / CaptchaFox /
                              // Friendly Captcha polling timeout
                              // (ALTCHA and Capy use defaultTimeout — neither is a browser solve)
    pollingInterval: 5);      // max seconds between res.php polls (starts at 0.25s, backs off to this)

Use environment variables in production:

# Linux / macOS
export CAPSKIP_API_KEY="your-key"
export CAPSKIP_HOST="127.0.0.1"
export CAPSKIP_PORT="8080"

# Windows PowerShell
$env:CAPSKIP_API_KEY = "your-key"
$env:CAPSKIP_HOST = "127.0.0.1"
$env:CAPSKIP_PORT = "8080"

using CapSkip;

var solver = new CapSkipClient(
    apiKey: Environment.GetEnvironmentVariable("CAPSKIP_API_KEY") ?? "capskip",
    host: Environment.GetEnvironmentVariable("CAPSKIP_HOST") ?? "127.0.0.1",
    port: int.TryParse(Environment.GetEnvironmentVariable("CAPSKIP_PORT"), out var p) ? p : 8080);

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Usage examples

Image captcha

await solver.NormalAsync("captcha.png");
await solver.NormalAsync("https://example.com/captcha.jpg");
await solver.NormalAsync("data:image/png;base64,iVBORw0KGgo...");
// result.Code holds the recognized text

reCAPTCHA v2 / v3

// reCAPTCHA v2
var v2 = await solver.RecaptchaAsync("...", "https://example.com");

// reCAPTCHA v3
var v3 = await solver.RecaptchaAsync("...", "https://example.com", new Dictionary<string, object?>
{
    ["version"] = "v3",
    ["action"] = "submit",
    ["score"] = 0.7,
});

Cloudflare Turnstile

var result = await solver.TurnstileAsync("0x4AAAAAAA...", "https://example.com");

GeeTest v3

gt is static per site, but challenge is single-use and expires in about a minute — fetch a fresh pair right before solving.

var result = await solver.GeetestAsync(
    "81388ea1fc187e0c335c0a8907ff2625",
    "7cf6a8b1a2c34d5e6f7089abcdef0123",
    "https://example.com/login");

// Post these back exactly as the site's own front-end would
result.Challenge; result.Validate; result.Seccode;

ALTCHA

ALTCHA is proof-of-work, not recognition — there is nothing to read, so a solve is deterministic and takes milliseconds. Give CapSkip the endpoint that serves the challenge, or the challenge document itself.

var result = await solver.AltchaAsync(
    "https://example.com/signup",
    new Dictionary<string, object?>
    {
        ["challenge_url"] = "https://example.com/captcha/api/altcha/challenge",
    });

// Post this back in the form field the widget uses, named `altcha`
result.Token;

Challenges expire fast — some sites inside two minutes — so fetch one immediately before solving and submit the token promptly.

Capy Puzzle

A Capy solution is not a token. It is three values that together go into the target form, so post all three back exactly as returned.

var result = await solver.CapyAsync(
    "PUZZLE_Abc1dEFghIJKLM2no34P56q7rStu8v",
    "https://example.com/login");

// capy_captchakey, capy_challengekey and capy_answer respectively
result.CaptchaKey; result.ChallengeKey; result.Answer;

Answer is the drag path the widget would have recorded — submit it verbatim, without trimming or re-encoding it. The challenge key is single-use and short-lived, so submit promptly rather than caching the three values.

Pass api_server when the widget script points somewhere other than https://jp.api.capy.me. Only the puzzle family is solved; ["version"] = "avatar" is refused rather than answered with a puzzle answer the site would reject.

CaptchaFox

var result = await solver.CaptchaFoxAsync(
    "sk_xtNxpk6fCdFbxh1_xJeGflSdCE9tn99G",
    "https://example.com/signup");

// Post this back in the form field the widget uses, named `cf-captcha-response`
result.Token;

// The UA the token was minted under — submit under this one, not your own
result.UserAgent;

url has to be the page the widget actually runs on: CaptchaFox checks it against the domains the key is registered for and refuses a mismatch permanently, not intermittently.

Pass api_server only when the page does not load the default widget. A page loading the MAM package expects a MAM_ prefixed token, and sending the wrong source still succeeds — it just returns a token the site will not accept, which reads as a silent verification failure rather than an error.

Friendly Captcha

Two different protocols ship under this name and a sitekey does not tell you which one a site uses, so say which — or send the widget script and let CapSkip read it off the build the site actually loads.

var result = await solver.FriendlyCaptchaAsync(
    "FCMGEMUD2M567T8G",
    "https://example.com/signup",
    new Dictionary<string, object?> { ["version"] = "v2" });

// v1 → frc-captcha-solution, v2 → frc-captcha-response
result.Token;

// Or let the script URL decide the version
var result = await solver.FriendlyCaptchaAsync(
    "FCMGEMUD2M567T8G",
    "https://example.com/signup",
    new Dictionary<string, object?>
    {
        ["module_script"] = "https://cdn.example.com/@friendlycaptcha/sdk@0.1.6/site.min.js",
    });

Solving the wrong version returns a well-formed token the target site rejects, with nothing to indicate the version was the problem. With neither version nor a script URL, v1 is assumed. Pass ["api_server"] = "eu" for a sitekey on the EU data-residency tenant. A v2 token is roughly six kilobytes, so size whatever carries it accordingly.

With a proxy (every method except image captcha)

// Proxy is not supported for image captcha
await solver.RecaptchaAsync("...", "https://example.com", new Dictionary<string, object?>
{
    ["proxy"] = new Proxy("HTTPS", "user:pass@1.2.3.4:3128"),
});
await solver.TurnstileAsync("...", "https://example.com", new Dictionary<string, object?>
{
    ["proxy"] = new Proxy("HTTP", "1.2.3.4:3128"),
});

Parallel solving

using CapSkip;

var solver = new CapSkipClient();
var results = await Task.WhenAll(
    solver.RecaptchaAsync("...", "https://a.com"),
    solver.TurnstileAsync("...", "https://b.com"));

Console.WriteLine($"{results[0].Code} {results[1].Code}");

AsyncCapSkip is provided as an alias of CapSkipClient — .NET I/O is asynchronous by nature, so every method already returns a Task. It exists for parity with the other CapSkip SDKs.

More examples: examples/

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Selenium, Playwright and PuppeteerSharp

The SDK hands back a token; your existing browser tooling does the driving. The shape is the same whichever you use:

1. Read the sitekey off the page (data-sitekey, or the widget's config object).
2. Call the matching solve method with that sitekey and the page URL.
3. Write the token into the response field and submit.

Selenium WebDriver

var sitekey = driver.FindElement(By.CssSelector("[data-sitekey]")).GetAttribute("data-sitekey");
var result = await solver.RecaptchaAsync(sitekey, driver.Url);

((IJavaScriptExecutor)driver).ExecuteScript(
    "document.getElementById('g-recaptcha-response').value = arguments[0];", result.Code);
driver.FindElement(By.CssSelector("form")).Submit();

Playwright for .NET

var sitekey = await page.GetAttributeAsync("[data-sitekey]", "data-sitekey");
var result = await solver.RecaptchaAsync(sitekey, page.Url);

await page.EvaluateAsync(
    "t => document.getElementById('g-recaptcha-response').value = t", result.Code);

PuppeteerSharp follows the same pattern with page.EvaluateFunctionAsync. Longer walkthroughs: Selenium, Playwright and Puppeteer.

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Return value

Every solve method resolves to a SolveResult:

public sealed class SolveResult
{
    public string CaptchaId { get; }  // internal ID from CapSkip
    public string Code { get; }       // solution — text for image, token for reCAPTCHA/Turnstile
    public string? UserAgent { get; } // Turnstile & CaptchaFox — the UA that minted the token
    public string? Challenge { get; } // GeeTest only — geetest_challenge
    public string? Validate  { get; } // GeeTest only — geetest_validate
    public string? Seccode   { get; } // GeeTest only — geetest_seccode
    public string? Token     { get; } // ALTCHA, CaptchaFox & Friendly Captcha — the payload to post back
    public long?   Number    { get; } // ALTCHA only — the counter that solved it
    public string? CaptchaKey   { get; } // Capy only — capy_captchakey
    public string? ChallengeKey { get; } // Capy only — capy_challengekey
    public string? Answer       { get; } // Capy only — capy_answer (the drag path)
    public string? RespKey      { get; } // Capy only — empty; carries nothing
}

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Error handling

All SDK exceptions derive from CapSkipError, so you can catch that one type — or handle each kind:

using CapSkip;

try
{
    var result = await solver.RecaptchaAsync("...", "...");
}
catch (ValidationException)   { /* invalid parameters */ }
catch (NetworkException)      { /* CapSkip not running, or captcha not ready (manual polling) */ }
catch (ApiException)          { /* API returned an error code */ }
catch (CapSkip.TimeoutException) { /* polling timeout exceeded */ }
catch (CapSkipError)          { /* any other CapSkip failure */ }

Note: CapSkip.TimeoutException and CapSkip.ValidationException share their short names with types in System. If you have both using System; and using CapSkip;, qualify them as CapSkip.TimeoutException / CapSkip.ValidationException, or just catch the base CapSkipError.

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FAQ

How do I solve a captcha in C#?

Install the CapSkip desktop app, dotnet add package CapSkip, then await the method that matches the widget — RecaptchaAsync(), TurnstileAsync(), GeetestAsync(), AltchaAsync(), CapyAsync(), CaptchaFoxAsync(), FriendlyCaptchaAsync() or NormalAsync(). Each returns a SolveResult whose Code is the token, or the recognized text in the case of an image captcha.

Is this a free captcha solver?

The SDK itself is MIT-licensed and free. Solving needs the CapSkip app, which is bought once rather than metered per captcha, so your cost stops scaling with volume.

Which captchas can it solve?

reCAPTCHA v2 (checkbox and invisible), reCAPTCHA v3, reCAPTCHA Enterprise, Cloudflare Turnstile, GeeTest v3, ALTCHA, Capy Puzzle, CaptchaFox, Friendly Captcha, and image/text captchas. Not hCaptcha, and not FunCaptcha/Arkose.

Does it work with Selenium and Playwright?

Yes — see above. The SDK never touches a browser itself, so it drops into whatever stack you already have, PuppeteerSharp and plain HttpClient included.

Which .NET versions are supported?

The package targets .NET Standard 2.0, which covers .NET 6 through 9+, .NET Core 2.0+, and .NET Framework 4.6.1+.

Why is my reCAPTCHA v3 score low?

Google derives v3 scores from IP reputation, cookies and browsing history. A solver returns a valid token, but it cannot change how Google grades that token — score is forwarded as the target you want, not a guarantee. If a site enforces a high threshold, solve through a cleaner IP using the proxy option.

Can I use it as a 2captcha alternative?

Yes. CapSkip serves the same endpoints, so you can either move to this SDK or repoint an existing 2captcha client at 127.0.0.1:8080.

Does the captcha have to be on a public page?

For widget captchas, yes — CapSkip loads the URL you pass it. Image captchas only need the image, and that can be a local file.

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Development

git clone https://github.com/capskip/capskip-dotnet.git
cd capskip-dotnet
dotnet test

The test suite mocks the HTTP layer and spins up a local mock server — no CapSkip app or network access required. See CONTRIBUTING.md for the full development workflow.

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Links

• CapSkip — local captcha solver · download the app
• Captcha demo pages — live reCAPTCHA, Turnstile, GeeTest and image widgets
• C# captcha solver guide
• HTTP API docs
• Other clients: Python · Node.js · PHP · MCP server for AI agents
• NuGet package · report an issue

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License

MIT — see LICENSE.