Status Codes

HTTP Status Codes – Quick Guide & Fixes

Ever run into an HTTP status code like 500, 404, or 301 and wondered what it means? Here’s a developer-friendly guide to the most common HTTP codes, what they mean, how to fix them, and how they impact SEO — especially when using JavaScript rendering solutions like Prerender.io.

1xx Informational Status Codes and Protocols

100 Continue

When does 100 Continue shows up? The 100 Continue status code shows up during large file uploads or chunked requests.
Browser/server logs: Rarely shown to users, but appears in dev tools or server logs.
SEO Impact of 100 Continue status code: None.
How to Fix 100 Continue: Usually no fix needed.
Prerender.io: Not altered or handled specifically.

101 Switching Protocols

When 101 Switching Protocols show up: The 101 Switching Protocol shows up when upgrading to a different protocol like WebSocket.
Browser/server logs: Seen in dev tools during live app interactions.
SEO Impact of 101 Switching Protocols: Minimal; bots don’t interact with WebSockets.
How to Fix 101 Switching Protocols: Ensure client and server agree on upgrade.
Prerender.io: Not applicable.

2xx Success Status Codes and Protocols

200 OK

When 200 OK status code shows up: Standard response for a successful GET or POST.
Logs: Seen when visiting a working URL.
SEO Impact of 200 OK status code: Ideal. Bots treat this as a healthy, indexable page.
How to Fix: None.
Prerender.io: Returns 200 when a page is rendered or cached. HTTP 200 also happens upon a request served from our cache. successfully. Docs

201 Created

When 201 Created shows up: After a successful POST that creates a resource.
Logs: Appears in API logs.
SEO Impact of 201 Created: Neutral unless linked.
How to Fix 201 Created: Ensure new pages are linked.
Prerender.io: Not specifically altered.

204 No Content

When 204 No Content shows up: Successful request with no response body.
Logs: Seen with form submissions or async calls.
SEO Impact of 204 No Content: Not indexable.
How to Fix 204 No Content: Add meaningful content or use 200.
Prerender.io: Will serve blank if nothing is rendered.

3xx Redirection Status Codes and Protocols

301 Moved Permanently

When 301 Moved Permanently shows up: Permanent redirect to a new URL
Logs: Redirects to new location.
SEO Impact of 301 Moved Permanently: Positive; passes link equity.
How to Fix 301 Moved Permanently: Update all internal links.
Prerender.io: Not cached.

302 Found

When 302 Found shows up: Temporary redirect.
Logs: Immediate redirect seen in dev tools.
SEO Impact of 302 Found: Can confuse bots.
How to Fix 302 Found: Use only if temporary.
Prerender.io: Followed, but does not cache.

304 Not Modified

When 304 Not Modified shows up: Tells browser to use cached version.
Logs: Indicates no change.
SEO Impact of 304 Not Modified: Improves crawl efficiency.
How to Fix 304 Not Modified: Ensure caching headers are correct.
Prerender.io: Converts to 200 for bots.

307 / 308 Redirects

When 307 / 308 Redirects shows up: Preserves request method.
Logs: Seen with POST/PUT redirects.
SEO Impact of 307 / 308 Redirects: Same as 301/302 depending on usage.
How to Fix 307 / 308 Redirects: Use correctly per request type.
Prerender.io: Follows redirect as defined, also not cached.

4xx Client Errors Status Codes and Protocols

400 Bad Request

When 400 Bad Requests show up: Malformed syntax or invalid request.
Logs: Invalid API or URL structure.
SEO Impact of 400 Bad Requests: Wastes crawl budget.
How to Fix 400 Bad Requests: Validate inputs.
Prerender.io: Returned for invalid URLs.

401 Unauthorized

When 401 Unauthorized show up: Authentication required.
Logs: Protected areas.
SEO Impact of 401 Unauthorized: Page not crawlable.
How to Fix 401 Unauthorized: Add correct auth.
Prerender.io: Returned for wrong token.

403 Forbidden

When 403 Forbidden shows up: Access denied.
Logs: Permissions issue.
SEO Impact of 403 Forbidden: Blocks bots.
How to Fix 403 Forbidden: Review access rules.
Prerender.io: Returned when the token is missing.

404 Not Found

When 404 Not Found shows up: Page doesn’t exist.
Logs: Broken links.
SEO Impact of 404 Not Found: Crawl waste, lost rankings.
How to Fix 404 Not Found: Redirect or recreate.

410 Gone

When 410 Gone shows up: Resource intentionally removed.
Logs: Permanent removal.
SEO Impact of 410 Gone: Tells bots to deindex.
How to Fix 410 Gone: Use when removing content.
Prerender.io: Use meta tag to signal 410.

429 Too Many Requests

When 429 Too Many Requests shows up: Rate-limited.
Logs: Excessive hits.
SEO Impact of 429 Too Many Requests: Bots throttled.
How to Fix 429 Too Many Requests: Add backoff, increase limits.
Prerender.io: Common, as it is the way Prerender works currently. Upon reaching the free tier limit, then we will reply with 429 to every request.

5xx Server Errors Status Codes and Protocols

500 Internal Server Error

When 500 Internal Server Error shows up: Generic server issue.
Logs: Code/config error.
SEO Impact of 500 Internal Server Error: Blocks bots.
How to Fix 500 Internal Server Error: Debug server.
Prerender.io: Returned on failure.

502 Bad Gateway

When 502 Bad Gateway shows up: Proxy server received invalid response.
Logs: Backend timeout or crash.
SEO Impact of 502 Bad Gateway: Blocks indexing.
How to Fix 502 Bad Gateway: Check upstream.
Prerender.io: Same as 504 in some failure cases.

503 Service Unavailable

When 503 Service Unavailable shows up: Server temporarily offline.
Logs: Maintenance or overload.
SEO Impact of 503 Service Unavailable: Treated as temporary.
How to Fix 503 Service Unavailable: Add retry header.
Prerender.io: Used if the subscription is canceled.

504 Gateway Timeout

When 504 Gateway Timeout shows up: Server didn’t respond in time.
Logs: Prerender timeout or error.
SEO Impact of 504 Gateway Timeout: Bots may retry.
How to Fix 504 Gateway Timeout: Improve load time.
Prerender.io: 504 gateway timeout does not necessarily happen for blank pages. A blank page can be HTTP 200 as well, not depending on the content.
504 gateway timeout happens usually when Prerender can not reach the server upon rendering the page.

Why Status Codes Matter for SEO & Rendering

Correct status codes ensure bots understand your site’s structure. When using Prerender.io, this becomes even more critical since bots depend on proper status responses from the rendered version.

✅ 200: Indexable
🚫 404/410: Removal from index
🔁 301/302: Redirects
🛑 500+: Blocks crawling
⏳ 503: Retry later

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