When a user clicks a link or queries an API on your site, they expect a smooth ride from idea to desired outcome. Instead, they hit a wall: a 4xx error. Resolving 4xx errors is about more than just erasing entries from log files; it is crucial for maintaining your website’s reputation and solid technology. Fortunately, you have what it takes to rebuild that road.
A 4xx error indicates that the user the browser or the client of an API, as the server will say made a request it just could not fulfill. But unlike a 5xx server-side meltdown, 4xx errors usually relate to a problem with the request structure, authorization, or perhaps a missing resource.
Effects on Technical Health score
Google places user experience at number one in everything on your website. When you encounter large numbers of errors from the crawler, it can appear to Google that your website is not being actively worked on, and your Technical health score efforts will be affected based on how you respond to each event. When you get 4xx errors on your website, every time that crawler comes to a dead end, you are wasting that one crawl out of your site’s crawl budget.
When you do nothing at all, you communicate to the search engine that no one is actively looking after this website.
You need to keep up with the logs in the client-side report. Is there internal pages on your website which are not working as internal links?
Or are there sites externally pointing to a dead page?
Correct these promptly and they count in your favor towards an increased site performance score.
The art of handling 4xx errors To address 4xx errors successfully, it should first be identified what constitutes 4xx errors.
400: Bad Request
You know things are getting sloppy when your server throws up its hands and says “I can’t even understand what you’re asking for, the syntax is all messed up!” It could be an invalid JSON payload from your frontend or the client’s just forgotten a header all together. The Fix: Validate all incoming data with a strong schema Library like Joi or Zod enforce the sanctity of your data BEFORE it even touches the core logic.
JavaScript
import { z } from 'zod';
// Define the schema for the incoming request
const UserSchema = z.object({
username: z.string().min(3),
email: z.string().email(),
});
// Inside your API route/controller
function createUser(req, res) {
const result = UserSchema.safeParse(req.body);
if (!result.success) {
// Return 400 if validation fails, preventing "sloppy" requests
return res.status(400).json({ error: "Invalid data", details: result.error });
}
// Proceed with valid data...
}401 & 403: Authentication vs.
Authorization You’ve probably seen them confused, but: 401 = ” I don’t know who you are” versus 403 = “I know who you are, but you don’t have the keys.” The Fix: Make sure your auth middleware does it’s job: handle expired tokens and correctly enforce roles. When possible don’t allow the unauthenticated to hit 403, force those into the 401 flow. 404: Not Found Yes, you know the one – probably the single most popular error code online.
It means that the request resource was nowhere to be found.
Sure some 404s can’t be helped as you mistype in a url and hit ENTER without looking, but other-wise, it could be broken internal links, or a db migration has gone sideways.
JavaScript
// Auth Middleware
function checkAccess(req, res, next) {
const token = req.headers.authorization;
// 1. Check if authenticated (401)
if (!token) {
return res.status(401).json({ message: "Authentication required" });
}
// 2. Check if authorized (403)
const userRole = getUserRole(token);
if (userRole !== 'admin') {
return res.status(403).json({ message: "You do not have the required permissions" });
}
next();
}How to Tackle Common Server Status Codes
You can’t be prepared for every potential issue. You can, however, control how a user feels when he’s run up against a broken page. One way to offer a top-notch user experience to even someone visiting a dead link is by using a custom 404 page (which displays when a requested page can’t be found).
When he lands on this page, give him some options: suggest a search, link to your site’s homepage, or point toward a help center or support page.
When people hit these helpful custom 404 pages, they’re much less likely to leave your site altogether and head back to the search results they just found.
The Developer’s Job Description When It Comes to Resolving Server Status Codes
1. Watch
Set up a service like Sentry or Datadog to ping you when the frequency of any 4xx error status code rises abnormally in your site’s requests. Such a tool also records the full request to record it for analysis. This monitoring is one of the few preventative measures developers take to address an error rate increase.
2. Analyze
You need to then dig deeper.
Did someone make a typo in your URL?
Did your frontend application attempt to request some resource from your API that no longer exists?
Did your backend actually return some data for you to utilize, or was the request just improperly submitted by the customer or an application trying to use your API? The former has more impact than a bad request which can be more quickly rectified.
3. Address
Depending on your analyses of step 2, what actions would you like for this 4xx error status code? If it’s that some particular link (the url that was typed in, by the way, or what your web application) just can not be served by some URL, then ideally you can use 301 redirect to send the request on over to the best and most relevant available content as you’re probably going to want your content index to remain healthy.
If not that your frontend client actually generated the bad request, your first go would perhaps be to consider improving your client-side validation and error handling mechanisms in place before pushing new features or even continuing business as usual on the site, given that no amount of SEO manipulation will rectify it.
JavaScript
// Example: Redirecting an old, deprecated path to a new, active one
// This tells search engines that the resource has moved permanently
app.get('/old-product-page', (req, res) => {
res.redirect(301, '/new-product-page');
});4. Monitor Again
As always when anything new is released to the site, it pays to monitor your response data. After the 4xx errors for a specific URL were all correctly redirected and there’s nothing more the team can actually do about it without rewriting or updating an article then those errors ought to go away.
