HTTP Status Codes Inspector & RFC Reference RFC 9110 Guide

Searchable RFC 9110 HTTP status codes reference guide covering 1xx, 2xx, 3xx, 4xx, and 5xx responses.

100

Continue

RFC 9110 §15.2.1

The server has received the request headers and the client should proceed to send the request body.

Troubleshooting & Resolution:

Normal for large POST/PUT requests using the "Expect: 100-continue" handshake header.

Non-Cacheable
101

Switching Protocols

RFC 9110 §15.2.2

The requester has asked the server to switch protocols and the server has agreed to do so (e.g. HTTP to WebSocket).

Troubleshooting & Resolution:

Check "Upgrade: websocket" and "Connection: Upgrade" request headers.

Non-Cacheable
103

Early Hints

RFC 8297 §2

Used to return some response headers before final HTTP message to allow preloading critical assets (Link preload).

Troubleshooting & Resolution:

Verify client/browser Link rel=preload header support.

Non-Cacheable
200

OK

RFC 9110 §15.3.1

The request has succeeded. Standard response for successful HTTP requests.

Troubleshooting & Resolution:

Inspect response payload and Content-Type header to ensure payload matches expectations.

Cacheable
201

Created

RFC 9110 §15.3.2

The request has been fulfilled, resulting in the creation of a new resource.

Troubleshooting & Resolution:

Response should ideally include a Location header containing the URI of the newly created resource.

Non-Cacheable
202

Accepted

RFC 9110 §15.3.3

The request has been accepted for processing, but the processing has not been completed.

Troubleshooting & Resolution:

Common in asynchronous background task queues. Look for polling status URL in response body.

Non-Cacheable
204

No Content

RFC 9110 §15.3.5

The server successfully fulfilled the request and there is no additional content to send in the response payload.

Troubleshooting & Resolution:

Standard for successful DELETE requests or save actions where no updated state is returned.

Cacheable
206

Partial Content

RFC 9110 §15.3.7

The server is delivering only part of the resource due to a Range header sent by the client.

Troubleshooting & Resolution:

Used in video streaming and resumable downloads. Check "Content-Range" and "Accept-Ranges" headers.

Cacheable
301

Moved Permanently

RFC 9110 §15.4.2

The target resource has been assigned a new permanent URI and any future references should use this new URI.

Troubleshooting & Resolution:

Critical for SEO. Search engines pass link equity to the Location target. Browser caches aggressively.

Cacheable
302

Found

RFC 9110 §15.4.3

The target resource resides temporarily under a different URI.

Troubleshooting & Resolution:

Historically caused method change (POST to GET). Prefer 307 or 308 for strict method preservation.

Non-Cacheable
304

Not Modified

RFC 9110 §15.4.5

Indicates that the resource has not been modified since the version specified by the request headers If-Modified-Since or If-None-Match.

Troubleshooting & Resolution:

Saves network bandwidth. Client uses local cached copy. Verify ETag and Cache-Control headers.

Cacheable
307

Temporary Redirect

RFC 9110 §15.4.8

The target resource resides temporarily under a different URI and the user agent MUST NOT change the request method.

Troubleshooting & Resolution:

Ensures POST data is re-sent with POST to the new location.

Non-Cacheable
308

Permanent Redirect

RFC 9110 §15.4.9

The target resource has been assigned a new permanent URI and the request method MUST NOT be changed.

Troubleshooting & Resolution:

Modern permanent redirect that strictly preserves POST/PUT request bodies. Strongly recommended for API upgrades.

Cacheable
400

Bad Request

RFC 9110 §15.5.1

The server cannot or will not process the request due to something that is perceived to be a client error.

Troubleshooting & Resolution:

Malformed request syntax, invalid JSON payload, or invalid query parameters.

Non-Cacheable
401

Unauthorized

RFC 9110 §15.5.2

The request has not been applied because it lacks valid authentication credentials for the target resource.

Troubleshooting & Resolution:

Check "Authorization: Bearer <token>" header, token expiration, or missing API keys.

Non-Cacheable
403

Forbidden

RFC 9110 §15.5.4

The server understood the request but refuses to authorize it. Authentication credentials were valid, but user lacks permission.

Troubleshooting & Resolution:

Role-based access control (RBAC) failure, CORS origin mismatch, or IP firewall block.

Non-Cacheable
404

Not Found

RFC 9110 §15.5.5

The origin server did not find a current representation for the target resource or is not willing to disclose that one exists.

Troubleshooting & Resolution:

Verify URL route, spelling, trailing slash policy, or deleted resource record in database.

Non-Cacheable
405

Method Not Allowed

RFC 9110 §15.5.6

The method received in the request-line is known by the origin server but not supported by the target resource.

Troubleshooting & Resolution:

Sending POST to a GET-only endpoint. Check "Allow" response header indicating supported methods.

Non-Cacheable
408

Request Timeout

RFC 9110 §15.5.9

The server did not receive a complete request message within the time that it was prepared to wait.

Troubleshooting & Resolution:

Slow client uplink, large uncompressed payload, or network drop.

Non-Cacheable
409

Conflict

RFC 9110 §15.5.10

The request could not be completed due to a conflict with the current state of the target resource.

Troubleshooting & Resolution:

Occurs in optimistic concurrency (version collision) or creating a resource with an existing unique email/username.

Non-Cacheable
422

Unprocessable Entity

RFC 9110 §15.5.21

The server understands the content type of the request entity, and the syntax is correct, but was unable to process the contained instructions.

Troubleshooting & Resolution:

Semantic validation errors (e.g. required form field missing, invalid email format, number out of range).

Non-Cacheable
429

Too Many Requests

RFC 6585 §4

The user has sent too many requests in a given amount of time ("rate limiting").

Troubleshooting & Resolution:

Inspect "Retry-After" header. Implement exponential backoff retry algorithms in API client.

Non-Cacheable
500

Internal Server Error

RFC 9110 §15.6.1

The server encountered an unexpected condition that prevented it from fulfilling the request.

Troubleshooting & Resolution:

Unhandled exceptions, database connection timeouts, or backend crash. Inspect server error logs.

Non-Cacheable
502

Bad Gateway

RFC 9110 §15.6.3

The server, while acting as a gateway or proxy, received an invalid response from an inbound server it accessed.

Troubleshooting & Resolution:

Reverse proxy (Nginx, Cloudflare, Traefik) cannot reach upstream Node/Python backend.

Non-Cacheable
503

Service Unavailable

RFC 9110 §15.6.4

The server is currently unable to handle the request due to a temporary overload or scheduled maintenance.

Troubleshooting & Resolution:

High CPU/memory exhaustion, auto-scaling delay, or active maintenance mode. Look for Retry-After header.

Non-Cacheable
504

Gateway Timeout

RFC 9110 §15.6.5

The server, while acting as a gateway or proxy, did not receive a timely response from an upstream server.

Troubleshooting & Resolution:

Upstream query took longer than proxy timeout (typically 30s or 60s). Optimize slow database queries.

Non-Cacheable
📖 Technical Documentation, RFC Specifications & FAQs ▼
Frequently Asked Questions (FAQ) · HTTP Status Codes Inspector & RFC Reference

HTTP Status Code Reference & Diagnostic Directory

Complete RFC 9110 compliant HTTP response status code lookup with diagnostic advice, caching semantics, and developer debugging tips.

MU
IBM Maximo & Developer Tools Architect
Technical Reference

01. RFC 9110 HTTP Status Code Architecture

HTTP response status codes are 3-digit integers issued by servers to communicate request outcomes across 5 standardized classes: 1xx Informational, 2xx Success, 3xx Redirection, 4xx Client Error, and 5xx Server Error.

Understanding specific nuances (such as 301 vs 308 redirects, or 401 Unauthorized vs 403 Forbidden) is critical for REST API design and SEO crawler indexation.

  • Complete directory from 100 Continue to 511 Network Auth Required.
  • Caching directives, idempotency semantics, and retry recommendations.
  • Diagnostic guidance for resolving common client and server errors.

02. Key HTTP Status Codes to Know

• `200 OK` & `201 Created`: Standard successful responses.

• `301 Moved Permanently` vs `302 Found`: Permanent SEO redirect vs temporary.

• `401 Unauthorized` vs `403 Forbidden`: Missing authentication vs insufficient permissions.

• `429 Too Many Requests`: Rate limit exceeded.

• `502 Bad Gateway` & `504 Gateway Timeout`: Upstream proxy failures.

03. API Diagnostics, Client Emulation & Request Pipeline

Inspect client User-Agent headers with our User-Agent Parser, convert curl terminal commands to production API client code with the cURL Converter, or test social crawler metadata using the Open Graph Builder.

Frequently Asked Questions (FAQ)

What is the difference between 401 and 403?

401 means unauthenticated (login required); 403 means authenticated but access is forbidden.

Is 308 better than 301 for API redirects?

Yes. 308 guarantees that HTTP methods (POST, PUT) are preserved during redirection.

Does this reference require internet connectivity?

No. The entire directory is cached locally in your browser.

How does local in-browser processing protect sensitive enterprise credentials?

All code runs inside your local browser memory. No data is ever sent to an outside server. Your keys, tokens, and code remain completely private on your device.

Can I use this tool offline or within air-gapped networks?

Yes. Once the page loads, it works fully offline. You can use it safely on airplanes, private corporate networks, and secure offline computers.

Does status code inspection support real-time network probing?

This tool is a client-side RFC 9110 specification inspector and troubleshooting guide. It evaluates status codes, headers, and caching directives in 0 ms without making network requests that could violate CORS.

Are outputs formatted according to official industry standards?

Yes. All conversions follow official web and data standards. This ensures your outputs work smoothly across Linux, macOS, and Windows systems.

Is my confidential data uploaded to external servers when using HTTP Status Codes Inspector & RFC Reference?

No. Core processing in HTTP Status Codes Inspector & RFC Reference executes in volatile browser memory without server uploads. Inputs to local tools are not logged on remote servers; optional cloud-assisted features require user consent.

Is HTTP Status Codes Inspector & RFC Reference free to use with any rate limits or paywalls?

Core tools are free to use without an account. Device memory and tool-specific safety limits apply. Optional AI and online contact services have usage limits.

Privacy and offline availability

Core tools process input locally. Optional AI sends the selected snippet through Cloudflare to Cloudflare AI or the optional Google Gemini fallback after consent; provider retention policies apply. Contact submissions send your details to our email provider. Offline use requires the page and its assets to finish caching; external AI and contact delivery require internet.

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Runs in Local Memory

Core tools run inside your web browser. Core tool inputs stay on your device; optional AI sends selected snippets after consent.

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Accurate Web Standards

Built to follow official web rules. Every tool is tested to ensure clean, accurate outputs.

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Works Offline Anywhere

Works without internet once loaded. Safe to use on airplanes, trains, and secure corporate networks.

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Zero Ads or Tracking

No advertising trackers. Optional external services are described in the privacy notice.

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