This document discusses APIs for mobile applications and provides 5 recommendations for building great mobile experiences through APIs. The recommendations are: 1) Keep API conventions consistent, 2) thoroughly document APIs, 3) maintain backwards compatibility in API versioning, 4) implement error handling and caching to insulate mobile clients from issues, and 5) design APIs specifically for mobile use cases and experiences rather than just exposing backend data. The document argues that mobile-optimized APIs can improve development speed and iteration, reduce bugs from client-specific implementations, and better support creating customized mobile experiences.

1. APIs for the
Mobile World
Michele Titolo
Lead Software Engineer @ Capital One

2. Why APIs for the
world?mobile

3. People 💖 Apps

4. Apps Have To Be
Great 👍

5. Apps Are
Complicated

6. 📶
🔗
🕐‼
👑

7. Can APIs make an
app not great? Yes.

8. How?

9. Slow 💤

10. State 🙅

11. Crashes 💥

12. Oops something’s amiss

13. Slows Down
Development

15. great📱
5ways to make
experiences

16. Keep Things Consistent.1

17. Established
Conventions

18. Don’t Return 200
With “Error”

19. Follow Your Own
Conventions

20. Endpoint “id” field
/products id
/products/:id productID
/cart product_id

21. Document Everything.2

22. does not
self documenting
code
exist

23. Ask So And So Is Not
Documentation

24. Update
Documentation

25. Communicate

26. Make
Documentation Part
Of The Process

27. Auto-Generate

28. Honor thy contracts.3

29. Documentation Is A
Contract

30. Versioning

31. Unexpected
Breaking Changes

32. http://

33. 500s that return
HTML

34. Insulate the client.4

35. Something
WILL PROBABLY
GO
WRONG

36. Long Release Cycles

37. Releasing An App
Doesn't Mean People
Will Use It

38. Gateway Or Reverse
Proxy

39. The Bigger Your
Ecosystem, The More
This Is Needed

40. Route To Different
Servers

41. Mutate Requests And
Responses

42. Zuul

43. Make an API just for
mobile
.5

44. Backend For
Frontend

45. Tailor APIs to Mobile
Experiences

46. Not A New Concept

47. Why?

48. Rest
Representational State Transfer
= Data

49. Imagine…

50. The most amazing movie
app in the world

51. Lets Add A
New Feature

52. Show nearby movie times

53. # Obtain a list of movies
GET /movies
# Obtain a list of nearby theatres
GET /theatres?lat=…&long=…
# Obtain the showing times for a theatre
GET /theatres/1234/times

54. server.makeMoviesRequest { (movieList, error) in
if error {
// handle error case
} else {
// handle success case
}
}

55. server.makeMoviesRequest { (movieList, error) in
if error {
// handle error case
} else {
// handle success case
}
}
server.makeTheatresRequest(lat,long) { (theatreList, error) in
if error {
// handle error case
} else {
// handle success case
}
}

56. var moviesRequestComplete: Bool = false
var theatresRequestComplete: Bool = false
server.makeMoviesRequest { (movieList, error) in
if error {
// handle error case
} else {
moviesRequestComplete = true
// do something with the data
}
}
server.makeTheatresRequest(lat,long) { (theatreList, error) in
if error {
// handle error case
} else {
theatresRequestComplete = true
// do something with the data
}
}

57. func makeInitialServerCalls () {
var moviesRequestComplete: Bool = false
var theatresRequestComplete: Bool = false
server.makeMoviesRequest { (movieList, error) in
if error {
// handle error case
} else {
moviesRequestComplete = true
// do something with the data
}
}
server.makeTheatresRequest(lat,long) { (theatreList, error) in
if error {
// handle error case
} else {
theatresRequestComplete = true
// do something with the data
}
}
}
func makeTheatreTimesRequest(for: theatres) {
for theatre in theatres {
server.makeTheatreTimesRequest(theatre.id) {
if error {
// handle error case
} else {
// process movie times
}
}
}
}

58. func makeInitialServerCalls () {
var moviesRequestComplete: Bool = false
var theatresRequestComplete: Bool = false
server.makeMoviesRequest { (movieList, error) in
if error {
// handle error case
} else {
moviesRequestComplete = true
self.movies = movieList
}
}
server.makeTheatresRequest(lat,long) { (theatreList, error) in
if error {
// handle error case
} else {
theatresRequestComplete = true
makeTheatreTimesRequest(for: theatreList)
}
}
}
func makeTheatreTimesRequest(for: theatres) {
let closestTheatres = theatres..3 // get 3 closest theatres
for theatre in closestTheatres {
if !requestTimesForTheatreAndReturnIfAnotherRequestShouldBeMade(theatre) {
break
}
}
}
func requestTimesForTheatreAndReturnIfAnotherRequestShouldBeMade(theatre) {
server.makeTheatreTimesRequest(theatre.id) {
if error {
// handle error case
} else {
// process movie times
}
}
}

59. func makeInitialServerCalls () {
var moviesRequestCompletedSucessfully: Bool = false
var theatresRequestComplete: Bool = false
server.makeMoviesRequest { (movieList, error) in
if error {
// handle error case
} else {
moviesRequestCompletedSucessfully = true
self.movies = movieList
}
}
server.makeTheatresRequest(lat,long) { (theatreList, error) in
if error {
// handle error case
layoutMovies()
} else {
theatresRequestComplete = true
if moviesRequestCompletedSuccessfully {
makeTheatreTimesRequest(for: theatreList)
}
}
}
}
func makeTheatreTimesRequest(for: theatres) {
let closestTheatres = theatres..3 // get 3 closest theatres
var theatreTimesAPIsFinished: Bool = false
for theatre in closestTheatres {
if !requestTimesForTheatreAndReturnIfAnotherRequestShouldBeMade(theatre) {
theatreTimesAPIsFinished = true
break
}
}
layoutMovies()
}
func requestTimesForTheatreAndReturnIfAnotherRequestShouldBeMade(theatre) {
server.makeTheatreTimesRequest(theatre.id) {
if error {
// handle error case
} else {
// process movie times
}
}
}
‼
❓
🚫
🙀
💩

60. Multiple Client
Implementations

61. More Bugs

62. Error Scenarios
Times Many

63. Release Dependent
Changes

64. Release Dependent
Experiments

65. Resource Based Apis
Make Creating
Experiences Difficult

66. Solution: Apis For
Mobile Experiences

67. Logic Has To Live
Somewhere

68. Easier To Release
And Iterate

69. Makes Mobile
Development Easier

70. Great Experiences

71. 1. Keep It Consistent
2. Document Everything
3. Honor Thy Contracts
4. Insulate The App
5. Make Something Special
In Summary

72. Thank You!
@micheletitolo

73. • https://unsplash.com/search/phone?
photo=0VGG7cqTwCo
• https://unsplash.com/search/phone?
photo=UGX2qdjdKkw
Photo Credits