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HTTP versions preserve the basic request/response model but change how messages travel over the network. HTTP/2 multiplexes streams over one TCP connection, while HTTP/3 uses QUIC to avoid some transport-level blocking between streams. These improvements affect connection efficiency, not the need for correct API semantics.

An HTTP status code describes the outcome of an HTTP request using a standard numeric category. Clients use it to decide whether to use a result, correct a request, authenticate or retry. A response body can add application details, but should not contradict the status code.

HTTP caching reuses a stored response when its cache rules allow it, reducing repeated work and data transfer. An ETag identifies a resource representation so the client can ask whether its saved version is still valid. Conditional requests allow the server to say “unchanged” without sending the full representation again.

CORS is a browser-enforced protocol that lets a server permit selected cross-origin response access. The browser checks response headers and may send a preflight request before the actual request. It is not a firewall: clients outside the browser can still call the API, and some cross-origin requests can be sent even without readable responses.

Pagination divides a large result set into manageable pages, while API versioning lets an interface change without unexpectedly breaking clients. Both are part of the API contract because callers depend on ordering, limits and field meaning. A good design remains predictable as the data and number of clients grow.

PUT is defined around creating or replacing the state of a target resource, while PATCH applies a described partial change. Idempotency means repeating an identical operation has the same intended server-side effect as doing it once. It does not require every repeated response to contain the same status or body.

A cookie is a small piece of browser-managed data sent automatically with matching requests. A server-side session uses an unpredictable identifier, often in a cookie, to look up login state on the server. This lets the server revoke or change that state without placing all session details in the browser.

HTTP versions preserve the basic request/response model but change how messages travel over the network. HTTP/2 multiplexes streams over one TCP connection, while HTTP/3 uses QUIC to avoid some transport-level blocking between streams. These improvements affect connection efficiency, not the need for correct API semantics.

An HTTP status code describes the outcome of an HTTP request using a standard numeric category. Clients use it to decide whether to use a result, correct a request, authenticate or retry. A response body can add application details, but should not contradict the status code.

HTTP caching reuses a stored response when its cache rules allow it, reducing repeated work and data transfer. An ETag identifies a resource representation so the client can ask whether its saved version is still valid. Conditional requests allow the server to say “unchanged” without sending the full representation again.

Pagination divides a large result set into manageable pages, while API versioning lets an interface change without unexpectedly breaking clients. Both are part of the API contract because callers depend on ordering, limits and field meaning. A good design remains predictable as the data and number of clients grow.

CORS is a browser-enforced protocol that lets a server permit selected cross-origin response access. The browser checks response headers and may send a preflight request before the actual request. It is not a firewall: clients outside the browser can still call the API, and some cross-origin requests can be sent even without readable responses.

PUT is defined around creating or replacing the state of a target resource, while PATCH applies a described partial change. Idempotency means repeating an identical operation has the same intended server-side effect as doing it once. It does not require every repeated response to contain the same status or body.

A cookie is a small piece of browser-managed data sent automatically with matching requests. A server-side session uses an unpredictable identifier, often in a cookie, to look up login state on the server. This lets the server revoke or change that state without placing all session details in the browser.

A stuck backend often means a shared resource is occupied or an operation has no effective deadline. The event loop, connection pool and external API each have different ways to become saturated. Identify which queue is growing before deciding whether to optimize work, cancel it, limit it or scale capacity.

JWT is a token format, not a role: an access token can be a JWT or another format. An access token authorizes calls to an API, while a refresh token is used with the identity service to obtain new access tokens. Separating these roles limits how long a stolen access token is useful and supports longer login sessions.

Slow responses, growing memory and 500 errors are symptoms, not root causes. A useful investigation connects each symptom to a specific route, instance, input or dependency. Comparing healthy and unhealthy requests often narrows the problem faster than changing settings blindly.

OAuth is a framework for delegated access, allowing a client to act with limited permission on protected resources. OpenID Connect (OIDC) adds a standard identity layer for user login on top of OAuth. The authorization code flow separates browser redirects from the token exchange and commonly uses PKCE to protect that exchange.

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