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A Fast and Easy to use microframework for the web.

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Crow is a C++ microframework for running web services. It uses routing similar to Python's Flask which makes it easy to use. It is also extremely fast, beating multiple existing C++ frameworks as well as non C++ frameworks.


  • Easy Routing (similar to flask).
  • Type-safe Handlers.
  • Blazingly fast (see this benchmark and this benchmark).
  • Built in JSON support.
  • Mustache based templating library (crow::mustache).
  • Header only library (single header file available).
  • Middleware support for extensions.
  • HTTP/1.1 and Websocket support.
  • Multi-part request and response support.
  • Uses modern C++ (11/14)

Still in development


Available here.


Hello World

#define CROW_MAIN
#include "crow.h"

int main()
    crow::SimpleApp app;

    CROW_ROUTE(app, "/")([](){
        return "Hello world";


JSON Response

CROW_ROUTE(app, "/json")
    crow::json::wvalue x;
    x["message"] = "Hello, World!";
    return x;


([](int count){
    if (count > 100)
        return crow::response(400);
    std::ostringstream os;
    os << count << " bottles of beer!";
    return crow::response(os.str());
Handler arguments type check at compile time
// Compile error with message "Handler type is mismatched with URL paramters"
([](int a, int b){
    return crow::response(500);

Handling JSON Requests

CROW_ROUTE(app, "/add_json")
([](const crow::request& req){
    auto x = crow::json::load(req.body);
    if (!x)
        return crow::response(400);
    int sum = x["a"].i()+x["b"].i();
    std::ostringstream os;
    os << sum;
    return crow::response{os.str()};

More examples can be found here.

Setting Up / Building

Available here.


CrowCpp/Crow is a project based on ipkn/crow. Neither CrowCpp, it's members, or this project have been associated with, or endorsed or supported by ipkn (Jaeseung Ha) in any way. We do use ipkn/crow's source code under the BSD-3 clause license and sometimes refer to the public comments available on the github repository. But we do not in any way claim to be associated with or in contact with ipkn (Jaeseung Ha) regarding CrowCpp or CrowCpp/Crow