HTTP Status Code Reference
NewComplete reference of all HTTP status codes with explanations, when to use them, and common causes. Searchable and categorized.
Meaning: Request headers received, continue body.
When to use: Expect: 100-continue flows.
Common causes: Large upload handshakes.
Example: Client sends headers first for a large upload.
Meaning: Server switches protocols.
When to use: WebSocket upgrade accepted.
Common causes: Upgrade header negotiation.
Example: HTTP connection upgraded to WebSocket.
Meaning: Server is processing long request.
When to use: WebDAV operations.
Common causes: Long-running write operations.
Example: Server confirms it is still working.
Meaning: Preload resources before final response.
When to use: Performance optimization.
Common causes: Server sends Link preload hints.
Example: Browser starts downloading CSS early.
Meaning: Request succeeded.
When to use: Normal successful GET/POST.
Common causes: Valid endpoint and payload.
Example: API returns requested user profile.
Meaning: Resource created successfully.
When to use: POST creates resource.
Common causes: Create endpoints.
Example: Order created and ID returned.
Meaning: Accepted for async processing.
When to use: Job queues/background tasks.
Common causes: Long task deferred.
Example: Video transcode job enqueued.
Meaning: Returned metadata may be transformed.
When to use: Proxy modified response metadata.
Common causes: Intermediary transformations.
Example: Proxy returns transformed headers.
Meaning: Success with no body.
When to use: DELETE/PUT with no response body.
Common causes: Successful update without payload.
Example: Settings updated successfully.
Meaning: Client should reset form/view.
When to use: After form submission.
Common causes: Action completed and UI reset needed.
Example: Form save response asks UI to clear fields.
Meaning: Partial range returned.
When to use: Range requests/download resumes.
Common causes: Streaming and resumable downloads.
Example: Video byte-range requested.
Meaning: Multiple status values in one response.
When to use: WebDAV multi-resource responses.
Common causes: Batch operations.
Example: Some files copied, some failed.
Meaning: Members already enumerated.
When to use: WebDAV propstat loops.
Common causes: Duplicate entries avoided.
Example: Depth traversal avoids repeats.
Meaning: Instance manipulation applied.
When to use: Delta encoding responses.
Common causes: Advanced cache/delta systems.
Example: Server returns diff instead of full resource.
Meaning: Multiple response options.
When to use: Content negotiation/manual choice.
Common causes: Resource has variants.
Example: User can pick language-specific resource.
Meaning: Permanent redirect.
When to use: Canonical URL changes.
Common causes: Domain/path migrations.
Example: Old blog URL redirects to new URL.
Meaning: Temporary redirect.
When to use: Short-term routing changes.
Common causes: Auth or temporary routing.
Example: Unauthenticated user redirected to login.
Meaning: Redirect using GET.
When to use: After POST to avoid re-submit.
Common causes: PRG pattern.
Example: Form post then redirect to receipt page.
Meaning: Use cached version.
When to use: ETag/If-Modified-Since cache validation.
Common causes: Client cache is fresh.
Example: Browser uses cached CSS file.
Meaning: Deprecated proxy instruction.
When to use: Legacy only.
Common causes: Old systems.
Example: Rarely used today.
Meaning: Reserved code.
When to use: Never in modern use.
Common causes: Historical placeholder.
Example: No practical usage.
Meaning: Temporary redirect preserving method.
When to use: Temporary move without method change.
Common causes: Maintenance and temporary routing.
Example: POST remains POST after redirect.
Meaning: Permanent redirect preserving method.
When to use: Permanent move with method safety.
Common causes: Modern permanent migrations.
Example: API endpoint moved permanently.
Meaning: Malformed request.
When to use: Invalid syntax/params.
Common causes: JSON parse errors, missing fields.
Example: Invalid payload schema submitted.
Meaning: Auth required or failed.
When to use: Missing/invalid credentials.
Common causes: Expired token.
Example: JWT missing in Authorization header.
Meaning: Reserved for future payment use.
When to use: Custom paywall semantics.
Common causes: Subscription checks.
Example: Premium endpoint behind billing.
Meaning: Authenticated but not allowed.
When to use: Permission denied.
Common causes: Role restrictions.
Example: Viewer tries admin action.
Meaning: Resource not found.
When to use: Unknown endpoint/resource ID.
Common causes: Bad URL/ID deleted.
Example: User ID does not exist.
Meaning: HTTP method not allowed here.
When to use: Endpoint exists but method invalid.
Common causes: GET on POST-only endpoint.
Example: DELETE sent to read-only route.
Meaning: Cannot satisfy Accept header.
When to use: Content negotiation failure.
Common causes: Unsupported media type response.
Example: Client requests XML, server only JSON.
Meaning: Proxy auth required.
When to use: Corporate proxy auth.
Common causes: Proxy challenge.
Example: Proxy asks for credentials.
Meaning: Server timed out waiting.
When to use: Slow or stalled client request.
Common causes: Network latency/user aborts.
Example: Upload stalled before completion.
Meaning: Request conflicts with current state.
When to use: Version conflicts/duplicates.
Common causes: Concurrency collisions.
Example: Attempt to create existing username.
Meaning: Resource intentionally removed.
When to use: Permanent deletion with intent.
Common causes: Deprecated resources.
Example: Legacy API removed permanently.
Meaning: Content-Length header required.
When to use: Server requires known body length.
Common causes: Chunked/unknown body sizes.
Example: Upload endpoint needs fixed length.
Meaning: Conditional headers failed.
When to use: ETag/version preconditions.
Common causes: Stale resource version.
Example: If-Match does not match current ETag.
Meaning: Request body too large.
When to use: File/JSON size limits exceeded.
Common causes: Upload limit exceeded.
Example: Image upload exceeds max MB.
Meaning: Request URI too long.
When to use: Huge query strings.
Common causes: Misused GET with massive params.
Example: Search filters encoded in giant URL.
Meaning: Request media type not supported.
When to use: Wrong Content-Type.
Common causes: text/plain sent instead of application/json.
Example: API expects JSON body.
Meaning: Invalid byte range.
When to use: Bad range requests.
Common causes: Range beyond file length.
Example: Resume download offset too high.
Meaning: Expect header unmet.
When to use: 100-continue expectations fail.
Common causes: Server doesn't support expectation.
Example: Client expected continue handshake.
Meaning: RFC joke code; often used playfully.
When to use: Easter eggs/test responses.
Common causes: Custom humorous API responses.
Example: Tea endpoint refusing coffee.
Meaning: Unofficial rate-limit style response.
When to use: Custom throttling.
Common causes: Client too aggressive.
Example: Legacy Twitter-style throttling.
Meaning: Request sent to wrong server.
When to use: HTTP/2 connection reuse mismatch.
Common causes: TLS/SNI mismatch.
Example: Shared connection wrong authority.
Meaning: Semantically invalid payload.
When to use: Validation errors.
Common causes: Field-level validation fails.
Example: Email format invalid in signup form.
Meaning: Resource is locked.
When to use: WebDAV locking.
Common causes: Concurrent write lock.
Example: Document locked by another editor.
Meaning: Dependent action failed.
When to use: Batch/transactional operations.
Common causes: Previous operation in chain failed.
Example: Move fails after lock step fails.
Meaning: Server unwilling to process replay-risk request.
When to use: Early data replay protection.
Common causes: TLS early data concerns.
Example: Server asks client to retry safely.
Meaning: Switch to newer protocol.
When to use: Require TLS/new HTTP version.
Common causes: Plain HTTP to HTTPS-only service.
Example: Server requires HTTPS upgrade.
Meaning: Conditional request required.
When to use: Prevent lost updates.
Common causes: Missing If-Match/If-Unmodified-Since.
Example: Update endpoint requires version check.
Meaning: Rate limit exceeded.
When to use: Throttle abusive/high-frequency clients.
Common causes: Burst traffic without backoff.
Example: Client exceeds 100 req/min.
Meaning: Headers too large.
When to use: Cookie/header bloat.
Common causes: Oversized cookies.
Example: Huge cookie payload rejected.
Meaning: Blocked by legal demand.
When to use: Geo/legal restrictions.
Common causes: Court/government takedown.
Example: Content blocked in specific region.
Meaning: Generic server failure.
When to use: Unhandled exceptions.
Common causes: App bugs/null pointers.
Example: Unexpected runtime exception.
Meaning: Server lacks requested functionality.
When to use: Method/feature unsupported.
Common causes: Endpoint stub not implemented.
Example: PATCH not supported by server.
Meaning: Invalid upstream response.
When to use: Proxy/gateway issues.
Common causes: Upstream crash/timeouts.
Example: Nginx receives malformed upstream response.
Meaning: Temporary server unavailability.
When to use: Maintenance/overload.
Common causes: Deployment or overload.
Example: App in maintenance mode.
Meaning: Upstream timed out.
When to use: Proxy timeout waiting upstream.
Common causes: Slow database/downstream service.
Example: API gateway timeout after 30s.
Meaning: HTTP version unsupported.
When to use: Client sends unsupported protocol.
Common causes: Old client/proxy mismatch.
Example: HTTP/0.9 style request rejected.
Meaning: Content negotiation config error.
When to use: Server negotiation loops.
Common causes: Misconfigured variants.
Example: Negotiated variant points to itself.
Meaning: Server storage exhausted.
When to use: WebDAV or storage-backed writes.
Common causes: Disk full/quota exceeded.
Example: Cannot save uploaded file.
Meaning: Infinite loop detected.
When to use: WebDAV depth operations.
Common causes: Cyclic bindings.
Example: Traversal loop breaks operation.
Meaning: Further extensions required.
When to use: Policy extension requirements.
Common causes: Missing extension declarations.
Example: Server expects additional extension info.
Meaning: Network login required.
When to use: Captive portals.
Common causes: Public Wi-Fi auth gates.
Example: User must login to Wi-Fi portal.
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About HTTP Status Code Reference
HTTP Status Code Reference is built for fast, reliable, browser-based workflows. It prioritizes clarity, predictable controls, and practical outputs that can be copied directly into real tasks. The interface is optimized for both desktop and mobile users, with responsive layouts and clear labels. Core interactions are designed around immediate feedback so users can iterate quickly without unnecessary steps. Where relevant, validation and guardrails reduce common mistakes before they reach production systems. The tool also integrates shareable URL state for smooth handoffs across teams, and keyboard execution for power users. Overall, the goal is to remove friction from repetitive operations while keeping output easy to verify and reuse.
Key Features
HTTP Status Code Reference core workflow
Focused UI designed for practical daily usage with immediate feedback.
Live calculations / preview
Updates output in real time as inputs change.
Copy-ready outputs
Important values are available with one-click copy controls.
Shareable params
Key state is preserved in URL query parameters for collaboration.
Keyboard execution
Primary action can be triggered with Ctrl+Enter / Cmd+Enter.
Mobile-first layout
Tool remains usable at narrow widths and touch interactions.
How to Use
- 1
Enter required input
Provide the input values needed for HTTP Status Code Reference and verify field validation.
- 2
Configure options
Set mode, filters, or selectors to match your target use case.
- 3
Run / update output
Trigger the action or use live mode to generate updated results.
- 4
Review details
Check highlighted insights, warnings, and supporting values.
- 5
Copy and share
Copy the final output and share a URL preserving current context.
Real-World Use Cases
Daily operations
A team member uses HTTP Status Code Reference during routine execution tasks to reduce manual effort.
Quality checks
A reviewer validates edge cases before publishing content or configuration changes.
Collaboration
A colleague shares exact tool state using URL params for faster troubleshooting.
Frequently Asked Questions
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