Code Quality Rank: L4
Programming language: Swift
License: BSD 2-clause "Simplified" License
Tags: Server    
Latest version: v0.4.0

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Frank is a DSL for quickly writing web applications in Swift with type-safe path routing.

import Frank

// Handle GET requests to path /
get { request in
  return "Hello World"

// Handle GET requests to path /users/{username}
get("users", *) { (request, username: String) in
  return "Hello \(username)"
import PackageDescription

let package = Package(
  name: "Hello",
  dependencies: [
    .Package(url: "https://github.com/kylef/Frank.git", majorVersion: 0, minor: 4)

Then build, and run it via:

$ swift build --configuration release
$ .build/release/Hello
[2016-01-25 07:13:21 +0000] [25678] [INFO] Listening at (25678)
[2016-01-25 07:13:21 +0000] [25679] [INFO] Booting worker process with pid: 25679

Check out the full example which can be deployed to Heroku.



Routes are constructed with passing your path split by slashes / as separate arguments to the HTTP method (e.g. get, post etc) functions.

For example, to match a path of /users/kyle/followers you can use the following:

get("users", "kyle", "followers") { request in


You may pass path components along with wildcard (*) to match variables in paths. The wildcard is a placemarker to annotate where the variable path components are in your path. Frank allows you to use any number of wildcards in any place of the path, allowing you to match all paths.

The wildcards will map directly to parameters in the path and the variables passed into your callback. Wildcard parameters are translated to the type specified in your closure.

// /users/{username}
get("users", *) { (request, username: String) in
  return "Hi \(username)"

// /users/{username}/followers
get("users", *, "followers") { (request, username: String) in
  return "\(username) has 5 followers"

You may place any type that conforms to ParameterConvertible in your callback, this allows the types to be correctly converted to your type or user will face a 404 since the URL will be invalid.

// /users/{userid}
get("users", *) { (request, userid: Int) in
  return "Hi user with ID: \(userid)"
Custom Parameter Types

Wildcard parameters may be of any type that conforms to ParameterConvertible, this allows you to match against custom types providing you conform to ParameterConvertible.

For example, we can create a Status enum which can be Open or Closed which conforms to ParameterConvertible:

enum Status : ParameterConvertible {
  case open
  case closed

  init?(parser: ParameterParser) {
    switch parser.shift() ?? "" {
      case "open":
        self = .open
      case "closed":
        self = .closed
        return nil

get("issues", *) { (request, status: Status) in
  return "Issues using status: \(status)"
Adding routes

Routes are matched in the order they are defined. The first route that matches the request is invoked.

get {

put {

patch {

delete {

head {

options {
Return Values

The return value of route blocks takes a type that conforms to the ResponseConvertible protocol, which means you can make any type Response Convertible. For example, you can return a simple string:

get {
  return "Hello World"

Return a full response:

get {
  return Response(.ok, headers: ["Custom-Header": "value"])

post {
  return Response(.created, content: "User created")

You can easily use the Stencil template language with Frank. For example, you can create a convenience function to render templates (called stencil):

import Stencil
import Inquiline
import PathKit

func stencil(path: String, _ context: [String: Any]? = nil) -> ResponseConvertible {
  do {
    let template = try Template(path: Path(path))
    let body = try template.render(Context(dictionary: context))
    return Response(.ok, headers: [("Content-Type", "text/html")], content: body)
  } catch {
    return Response(.internalServerError)

Which can easily be called from your route to render a template:

get {
  return stencil("hello.html", ["user": "world"])
    Hello {{ user }}!


Frank is design around the Nest Swift Web Server Gateway Interface, which allows you to use any Nest-compatible web servers. The exposed call function is a Nest compatible application which can be passed to a server of your choice.

import Frank

get {
  return "Custom Server"

// Pass "call" to your HTTP server