Are you about to ship a fresh REST endpoint and feeling that little twitch of fear? Will your next tweak break someone else’s production at three in the morning? How do you do API versioning without pulling rugs from under your users?
Why version at all if REST is supposed to be stable?
Because real apps grow. New fields arrive. Old mistakes need fixing. The moment your API gets even modest traffic, every change becomes a bet. On one side, progress for your product and your team. On the other, a support queue full of “your API broke our app.” Right now we are all watching the Twitter API get hammered by clients that update at different speeds. Facebook is opening more endpoints. iPhone apps are calling JSON all day. Carriers and proxies meddle with headers. There is almost no chance you can freeze an interface and call it a day. You need a plan that balances backward compatibility with the room to move. And you need it before your API shows up on Mashable and a thousand clients bake in today’s quirks forever.
So versioning is not a feature. It is a promise.
The contract you are actually signing
When you say “REST,” what you are really telling consumers is this: a resource has a name, it has a shape, and it behaves the same way tomorrow as it does today. Some change is friendly. You can add new fields to responses and most clients will ignore them. You can add optional parameters. You can introduce new resources and new links. That is the additive path and it keeps clients happy. The dangerous stuff is removing fields, changing types, renaming, or changing status codes in ways that flip the meaning of a response. Those are breaking changes. Versioning gives you a controlled place to do that work while protecting current callers. The trick is to keep your default path stable while you prepare a new space to evolve.
Protect production first, then move fast in a sandbox that clients choose.
Where to put the version so it does not hurt
You have three common choices today: in the path, in a header, or in a query string. Path versioning looks like putting v1 in the URL. It is easy to document, visual, and works with caches and proxies without special rules. Header based versioning uses Accept with a custom media type. It is tidy and keeps the URL stable. Many clients and load balancers still treat headers as second class though, and some tools trim them or change them. Query string puts version in a parameter. It is flexible, but some caches ignore query strings or treat them as uncacheable by default. If you want the least drama across today’s common stacks, path versioning wins for simplicity and cache friendliness. If you have clients that really care about content negotiation, headers can shine, but expect more support questions.
Pick one and stick to it.
Rules of the road for a stable v1
Make v1 boring. That is a compliment. Keep v1 alive as long as you have active clients on it. For changes that do not break, keep shipping them into v1. Add fields. Add endpoints. Avoid removing or renaming. When you absolutely must break, move to v2 in a way that is clear and measured. Do not yank v1 without a grace window and a plan to help users migrate. Publish a deprecation schedule with dates and reminders. Send email. Put warnings in response headers like Sunset with an exact date and a Link to docs. Give yourself a quiet period after each breaking change where the team watches errors and can roll back quickly if needed.
Stability is a feature users can feel.
Design for additive change first
The cheapest versioning strategy is the one you do not need. Design responses that can grow gracefully. Include links to related resources so clients discover relationships instead of hard coding them. Favor objects over arrays when you expect growth, since you can add keys without shifting positions. Use clear types and avoid overloading a field’s meaning. Provide default values that make sense when clients do not pass optional parameters. Consider a single top level object in JSON so you can add siblings later without surprising clients that index into a bare array. These small choices let you ship features today that will not turn into traps tomorrow.
Future you will send snacks to past you for that.
Communicate version in headers even when you use the path
Even if you place v1 in the URL, echo the current version in a header. Something like API Version with the string value. Add a Warning header when a route is on a deprecation path. Provide a Link header to the migration guide and to the v2 equivalent. This makes it easy for client libraries and monitoring tools to spot trouble. It also lets your support team ask users for a curl and see instantly which version they are hitting. Keep ETag and Last Modified solid so caches behave. These details sound small, but they cut a lot of back and forth when things go sideways.
Visibility beats guesswork.
Do not version everything
Resist the urge to slap a version tag on every concept. Version the contract not each field. If you have a user resource, the user shape belongs to a version of the API. Individual fields do not carry their own version flags. If you need experimental features, create a clear prefix like /experimental or a header flag that is off by default. That keeps your main version stable and gives curious clients a playground. Just promise nothing inside the experimental area. You will save yourself from locking in half baked ideas by accident.
Clean lines help real teams ship.
Set expectations in your docs and stick to them
Docs are part of the API. State your guarantees up front. Which kinds of changes are safe in v1. How long you keep a version alive after announcing deprecation. Where clients can subscribe for change notices. Show examples that tolerate extra fields. Note the typical status codes for each route. If you move to v2, write a migration guide that maps old responses to new responses and calls out any behavioral change. Keep a change log page and a feed. Many teams skip this and end up explaining the same thing in support threads over and over. Write it once, keep it current, link it everywhere.
Good docs are a cheat code for fewer tickets.
Deprecation without drama
Give people time and tools. Announce the deprecation with a target date. Add the Sunset header with that date. Start counting usage of the old version per consumer key so you know who is still calling it. Send friendly nudges as the date gets close. Provide a test environment where developers can try v2 with their data. When the date arrives, consider a limited block window for a subset of clients while you work with stragglers. It is tempting to drop the old version and move on. You will pay for that later with trust. Your API is part of someone else’s product. Treat it that way.
Trust compounds, so protect it.
Make logs and metrics your early warning system
As you roll out a new version, watch a few key signals. Track errors by route and version. Track latency by route and version. Watch cache hit rates. Watch spike patterns from popular client libraries. If you can, tag requests with the client name and version. This is gold during a migration. You can spot which library is sending bad payloads and reach out to the maintainer. You can see which endpoints turn chatty on mobile networks. With this in hand, you can adjust timeouts, add stronger validation, or update docs before a small issue becomes a public outage thread.
Measure twice, page once.
Pick a versioning story and write it down
If I had to boil it down for teams today, I would choose this plan. Put the version in the path for clarity and caching. Keep v1 steady and additive. Echo version info in headers. Add a deprecation header and a Link to docs when needed. Give a clear window before turning anything off. Design for growth so new fields do not break current clients. Keep the docs sharp and the change log active. Watch metrics by version. And be generous with communication. This is not sexy work, but it lets your product move without waking the entire client base at odd hours.
Simple, boring, repeatable.
Version to move forward without pulling rugs from the people who trusted you.