Designing an API is easy.
Evolving it without breaking your users is the real challenge. 🧩
Here’s a quick rundown of what usually breaks clients vs what you can do safely (most of the time 😉).
🔸 TL;DR
▪️ 🚫 Breaking changes force clients to update (or they crash).
▪️ ✅ Backward-compatible changes let existing clients continue to work.
▪️ 🧠 Always ask: “Will existing clients still behave correctly if they don’t change a line of code?”
🔸 WHAT COUNTS AS A BREAKING CHANGE? 💥
These changes can break existing consumers, even if your code still compiles:
▪️ ❌ Removing an endpoint
Clients calling /v1/orders will start failing if you just delete it.
▪️ 🔁 Changing response data structure
Renaming fields, changing nesting, or switching types (e.g. string → number) often breaks JSON parsing & mapping.
▪️ 🔍 Modifying query parameters
Making a previously optional parameter required, renaming or removing parameters breaks existing calls.
▪️ 🔐 Altering authentication methods
Removing API keys in favor of OAuth2 without a transition period will lock out clients.
▪️ 🧪 Changing endpoint behavior
Same signature, different semantics (e.g. pagination logic, default filters, or status codes) can silently break assumptions.
🔸 WHAT’S BACKWARD-COMPATIBLE? 🛟
These are usually safe for existing clients (as long as they ignore what they don’t know):
▪️ ➕ Adding optional fields
Existing clients can ignore new JSON fields while new clients start using them.
▪️ 🆕 Adding new endpoints
/v2/orders/summary can live alongside /v1/orders without breaking anything.
▪️ 📦 Extending response data
Adding extra info to the response (without changing existing fields) is fine if clients are tolerant readers.
▪️ 🔍➕ Adding query parameters
New optional parameters that enhance filtering or sorting are safe — old clients don’t have to send them.
▪️ 📚 Enhancing documentation
Better docs, examples, error descriptions, and contracts make your API safer to evolve.
🔸 TAKEAWAYS 🧭
▪️ 🧨 Treat breaking changes as rare, heavily communicated events (versioning, deprecation, migration guides).
▪️ 🧩 Prefer backward-compatible evolution to keep clients working while you improve the API.
▪️ 🔍 Before any change, ask: “Will existing clients still work exactly as yesterday?”
▪️ 📢 Communicate changes clearly: changelog, release notes, API docs, deprecation warnings.
#API #REST #WebAPI #SoftwareDesign #BackwardCompatibility #Microservices #DeveloperExperience #DX #CleanArchitecture #BreakingChanges
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