Find the outcome you need.
Start with a symptom, a platform or the thing you want working.
With JavaScript, search filters the whole collection in your browser. Without it, use the linked pages and section navigation below; query filters need JavaScript.
Showing entries 481–520 of 651 in this first collection.
Troubleshooting guide
Python 3.9 or 3.10 to 3.13: what was removed, and why compiled packages may not install
The standard-library modules removed in Python 3.12 and 3.13, how to find them in your code and dependencies, and how wheel tags and pinned requirements decide whether an install works.
Troubleshooting guide
Moving off Heroku: list the Procfile, release command, config names, add-ons and jobs first
What a Heroku app depends on outside its repository, how each item behaves according to Heroku's documentation, and how to list them without exposing a single secret.
Troubleshooting guide
Copying a Heroku Postgres database out: capture, download, rehearse the restore and reconcile
How Heroku's logical backups work, why a restore deletes the target first, the snags the documentation names, and what to compare before a final copy.
Troubleshooting guide
Upgrading Rails 7.x: take each minor version separately and read what changes
Why the Rails guide asks for one minor version at a time, what the guide lists for each 7.x step, and how framework-defaults files let you adopt changes gradually.
Troubleshooting guide
A Rails 6 app stuck before 7.0: run the Zeitwerk check and read what it reports
Zeitwerk autoloading is mandatory from Rails 7.0. How to check an app's file and constant names, what typical failures mean, and why eager loading is the real test.
Troubleshooting guide
Webpacker is retired: your Rails JavaScript options and what each means for an upgrade
What 'retired' means for a Rails app, the three successors its README names, and how to inventory what Webpacker does for you before choosing.
Troubleshooting guide
Changing a column on a large table: add, backfill, reconcile, switch, and only then drop
Why a single ALTER can lock or rewrite a big table, what the PostgreSQL and MySQL documentation say about each form, and how a stepwise change keeps a way back.
Troubleshooting guide
Reading vendor support dates: upstream, host, scheduled and final are different things
How Node.js, Python, Rails, Ruby, PostgreSQL and MySQL each publish support information, why the words differ, and what to record when you plan an upgrade around a date.
Troubleshooting guide
Before you change a version, record what your tests say today
A baseline run turns 'the upgrade broke it' into evidence. Three honest baseline states, what a green suite does not cover and what to do when there are no tests.
Platform
Rails upgrades: keep the Ruby, framework and JavaScript decisions apart
A Rails upgrade is three separate moving parts. Name which one is blocking you, and what each vendor still supports, before choosing a job.
Platform
Node.js upgrades: the runtime line, the framework major and native modules are different jobs
Choose the Node.js line from the project's own schedule, then handle a web-framework major version and compiled modules as separate, testable steps.
Platform
Python upgrades: choose the interpreter, then deal with removed modules and compiled packages
Use the Python developer guide's support dates, then separate standard-library removals, dependency wheels and framework majors so each can be tested.
Platform
Leaving Heroku: list everything the app depends on before choosing the new host
A Heroku app is its code plus a Procfile, a release command, config variables, add-ons, scheduled jobs and a database. List them before picking where to go.
Collection
Users cannot stay signed in: work through the failure in this order
An ordered process map from the provider error to the session cookie, showing which check separates each cause and which bounded repair fits, before any code is changed.
Collection
A page that is slow, jumpy, broken on a phone or missing from search: check in this order
An ordered process map for one page or section, from measurement through speed, layout shift, mobile layout, keyboard use and addresses, with the evidence that separates each.
Buyer collection
For a founder or product owner: make your web app's sign-in, forms and integrations dependable
Choose between a single repair, a set of flows made dependable together and a weekly check, and know what to prepare so the first conversation is about your app and not about access.
Buyer collection
For an agency lead: hand over a client site section with evidence on speed, accessibility and URLs
Turn a vague "make it good" request into a written standard for one section, a results table the client can read and a clear line between what is fixed and what is out of scope.
Inspectable example
Synthetic webhook test vector: why a re-formatted body makes a genuine event fail verification
Five versions of one made-up event, each shown in full with its real SHA-256 digest, show that re-formatting the body changes the hash and that a one-character change is rejected.
Inspectable example
Synthetic sign-in callback matrix: eight addresses an app might send, and why five of them fail
A made-up registered callback list and eight addresses an app could send show exact string matching: scheme, host, slash, port and a changing preview host each cause a mismatch.
Inspectable example
Synthetic redirect test sheet: nine old addresses, a loop, a chain and an unrelated destination, before and after
A made-up old-to-new map, with its rules and a short test script printed in full, is checked before and after a fix. The sheet records status codes, hops and final address, and shows how each fault is named and fixed.
Inspectable example
Synthetic screen-states matrix: seven cases for one orders list, each with a response, a screen and a test
A made-up orders screen shows how to write loading, empty, failed, timeout, server-error and missing-field cases as a table that a test per row can prove.
Troubleshooting guide
Can your sign-up or checkout flow be finished with a keyboard alone? A test script and the focus rules behind it
Keyboard operation, focus order, a visible focus indicator and focus not hidden by a sticky banner are four separate WCAG 2.2 checks. Run them on one flow before paying for an audit.
Troubleshooting guide
Form fields without labels and errors nobody hears: the three WCAG checks that fix most form failures
Visible labels, an error in text that names the field and a status message announced without moving focus. What each WCAG 2.2 criterion asks for and how to test it.
Troubleshooting guide
Sign-in fails with a redirect URI mismatch? Compare the two addresses character by character
A redirect mismatch is a string comparison that failed. Find the address your app really sends, compare it with the provider list and fix the right side.
Troubleshooting guide
Provider sign-in works but your app rejects the return? Check state, verifier and a callback handled twice
When the provider approves the user and your callback still fails, the missing piece is usually a stored state or verifier value, or a one-time code that was used twice.
Troubleshooting guide
Login succeeds then sends you back to the login page? Read the session cookie the browser actually keeps
A login loop usually means the browser refused or never returned the session cookie. Use this table of attributes to find which one without sharing a single cookie value.
Troubleshooting guide
Login works locally but loops behind a proxy or load balancer: the app may think it is on plain HTTP
A reverse proxy often ends HTTPS and passes plain HTTP to your app. If the app does not trust the forwarded protocol, secure cookies and callback addresses go wrong.
Troubleshooting guide
Slow Largest Contentful Paint? Split the delay into four parts before you change anything
Compressing images is the usual first move and often the wrong one. Find which of four parts of the load time is long, then fix that part.
Troubleshooting guide
Lighthouse says pass and the search report says fail? Lab runs and real-visitor data answer different questions
A lab test is one controlled load; real-visitor data is a 28-day average across devices. Know which one to use for debugging, which for the verdict and how to set a fair pass.
Troubleshooting guide
Page content jumps while it loads? Reserve the space before the image, font or embed arrives
Layout shift happens when something loads late and pushes content. Give images, embeds and fonts their space early and animate with transforms.
Troubleshooting guide
Supabase returns an empty list with no error? Find the missing policy before you switch protection off
With row-level security on, a table without a matching policy returns nothing. Check the signed-in role, the operation and the column, in that order, on a copy.
Troubleshooting guide
Next.js "hydration failed" or text does not match the server HTML? The documented causes and the safe order of fixes
Hydration errors mean the first browser render differs from the server HTML. Find the specific cause, from invalid nesting to dates, before reaching for suppressHydrationWarning.
Troubleshooting guide
A white screen or a spinner that never stops? What React error boundaries catch, and the cases they do not
An error boundary covers errors thrown while rendering. Request failures, empty results and errors in event handlers need their own handling, or users see a blank page.
Troubleshooting guide
Page scrolls sideways or content is cut off on a phone? Find the one element that is too wide
A sideways scroll bar means one element is wider than the screen. Common causes: a flex item that will not shrink, a missing viewport tag, a full-height section and long unbroken text.
Troubleshooting guide
Old pages return 404 after a relaunch? Build a one-to-one redirect map and test every hop
A redirect map pairs each old address with one right destination. Use permanent server-side redirects, avoid chains and unrelated destinations, and test the whole list.
Troubleshooting guide
Search reports show duplicates, blocked or redirected pages? Make canonical tags, sitemap and robots rules agree
Canonical tags, the sitemap and robots.txt each tell search engines something different. When they contradict each other, pages are skipped or grouped wrongly.
Troubleshooting guide
Webhook signature check fails on genuine events? Verify the exact bytes the provider signed
A signature is a hash of exact bytes. Parsing the JSON and re-serialising it, a proxy that rewrites the body or the wrong secret each change the hash. Find which, safely.
Troubleshooting guide
The same webhook arrives twice and runs twice? Acknowledge fast and make a repeat do nothing
Providers redeliver events that time out or fail. An endpoint that does the work before answering, with no memory of what it has seen, will run the action twice.
Troubleshooting guide
Junk keeps arriving through your web form: why browser checks do not stop it and what does
Scripts post straight to the address behind the form and skip the page. Validate on the server, then add a few low-friction controls and test them against real-looking junk.
Troubleshooting guide
Your form tells real customers their name or email is invalid: loosen the rule, not the standard
Over-strict checks turn away real people. Check names and email addresses against how they really work, and keep a genuine test set that must always pass.