Why Your Password Keeps Getting Rejected (and How to Fix It Without Making It Weaker)

The short answer: a rejected password is usually not a weak password — it is a strong password breaking one of the site's hidden rules. The most common culprits are a maximum length the form never mentions, a banned symbol, a password that appeared in a past data breach, a rule against using part of your username, or spaces being silently trimmed at one end of the process and not the other. The fix is almost never "pick something simpler." It is to find which rule you tripped, change only that one thing, and keep the length and randomness that made the password strong in the first place.

Diagnose it first: match the message to the cause

Most sites show a vague error — "password does not meet requirements" — and leave you guessing. Use this table to narrow it down before you start changing things at random:

1. The maximum length nobody told you about

This is the single most common cause of a "strong password rejected" mystery, and it mostly hits banks, government portals and older enterprise systems. You generate a 24-character password, the signup form accepts it without complaint, and then login fails forever — because the form silently cut your password down to, say, 16 characters when you created it, but checks the full 24 when you log in (or the reverse). The two ends of the process disagree about what your password is, and no error message ever says so.

The official guidance is on your side here: the OWASP Authentication Cheat Sheet says a maximum password length should be at least 64 characters, precisely so passphrases fit, and warns implementers not to silently truncate passwords. A site capping you at 16 characters is behind that guidance — but you still have to live with its rules. The fix is to generate a fresh password at or under the site's cap, using every character type the site allows. A 16-character fully random password is still enormously strong; what weakens passwords is not a 16-character cap, it is a user responding to the cap by falling back to something memorable. If a site gives no visible maximum, try 20 characters first — most caps sit at 16, 20 or 32 — and test the login immediately after signup, before you trust the stored copy.

2. A banned symbol hiding in an otherwise perfect password

Some sites ban specific symbols — often <, >, ", backticks, or spaces — because of how their own code handles input, not because those symbols are unsafe in a password. The rejection message rarely names the banned character, so the debugging trick is simple: generate the same password with symbols turned off. If it is accepted, symbols were the problem; then turn symbols back on one group at a time, or just accept a letters-and-digits password that is a few characters longer. Length compensates for a smaller character set quickly: dropping symbols costs roughly half abit of entropy per character, and adding four characters buys back far more than that. CISA's strong-password guidance makes the same trade in the other direction — it recommends long, random, unique passwords and a password manager, not any particular symbol count. What matters is that the final password is still generated, still random, and still unique to that site.

3. Your password appeared in a data breach — even if you invented it yesterday

Modern signup forms increasingly check new passwords against lists of credentials exposed in past breaches, and reject any match. This catches people by surprise in two ways. First, a password you consider original may genuinely be a common one — a short phrase, a keyboard pattern, a team name with a year — that has leaked thousands of times. Second, a password you generated and reused somewhere else may have leaked from that other site, so it is now on the list even though you never shared it publicly. Either way, the correct response is never to tweak the rejected password ("add a 1 at the end") and resubmit: the tweaked version is usually one guess away from the breached one. Generate a completely new password instead. This check is also one of the few password rules that genuinely improves security, and it is the reason NIST's digital identity guidance recommends screening new passwords against blocklists of common and breached values rather than piling on composition rules. If a site tells you a password was breached, believe it, and treat any other account using that password as exposed too.

4. Rules about your own name, email or username

Many forms reject passwords containing your username, your real name, or the part of your email before the @ sign — and they do it with a generic message that never says which fragment matched. This is worth knowing because it is the one rejection a password generator can trigger by pure chance: a random string can coincidentally contain a short username fragment, especially if your username is short. The fix is the same as everywhere else in this post: generate again. A fresh random draw almost certainly clears the rule, and it costs nothing. Do not respond by building the password around your name in a "clever" way (a nickname plus a year, a reversed username) — that is exactly the kind of predictable structure these rules exist to block, and it is also exactly what dictionary-based cracking tries first. For the full picture of why predictable structure fails even when it looks complex, see our complete password security guide.

5. Spaces: trimmed, rejected, or both — inconsistently

Spaces are the quietest cause of signup-works-login-fails. Some forms strip leading and trailing spaces when you create the password but not when you log in, or reject spaces outright with a message about "invalid characters," or accept a passphrase with spaces at signup and then fail it at login because a different code path handles the check. The OWASP cheat sheet's position is that verifiers should allow all characters, including whitespace — but plenty of real sites do not. The practical rule: never start or end a password with a space, and if a passphrase with internal spaces is rejected, generate a random-character password for that site instead of fighting its space handling. And whenever you set a password anywhere, log out and log back in immediately. That thirty-second test catches every trimming and truncation mismatch while you still remember what you typed and can still fix it.

6. When the password manager or the paste is the problem

If typing a password works but pasting it does not, suspect the field, not the password. Some forms set a hidden maximum length on the input that cuts a pasted password short without telling you; some password-manager autofill flows fill an old saved value instead of the new one; and some sites deliberately block pasting into password fields (a practice NIST discourages, since it pushes people toward weaker, typable passwords). Work through it in order: check whether the saved entry in your manager actually matches what you just generated, try typing the first and last few characters by hand after pasting, and look for a visible character counter on the field that reveals a cap. If pasting is blocked outright, type the password once, save it in the manager immediately, and verify with a fresh login — then let the manager handle it from then on. The goal is unchanged throughout: one unique, generated password per site, stored in the manager, not memorized and not reused.

Choosing the best password generator for strict sites

Strict sites are exactly where a generator earns its keep, because hand-editing a password to satisfy a rule usually weakens it. The best password generator for this job is one that lets you control the rules before generating: set the exact length the site allows, switch off exactly the banned symbols, and generate again until the site accepts it — without ever falling back to a password you invented. That is the workflow that keeps a 16-character capped password, a symbols-banned password, and a passphrase all equally strong: the randomness comes from the generator, and your only job is matching the site's stated limits. Generate a compliant password with the length and character set the site actually allows, save it straight into your password manager, and test the login before you move on. If the site rejects even that, work through the table at the top of this post one row at a time — the cause is in there, and it is a rule, not a weakness in your password.

FAQ

Why does a site reject a password my generator says is strong?
Because "strong" and "accepted" measure different things. Strength is about how hard the password is to guess; acceptance is about the site's own rules — maximum length, allowed symbols, breached-password lists, and bans on username fragments. A password can be unguessable and still break one of those rules. Find the rule, change only that, and the password stays strong.

What is the best free password generator for sites with strict rules?
The best free password generator for strict sites is one that generates entirely in your browser, lets you set an exact length, and lets you switch individual character types on and off — so you can match a 16-character cap or a symbols ban without inventing the password yourself. Generate within the site's rules, save it in a password manager, and test the login immediately after signup.

Is a shorter password still safe if a site caps the length?
Yes, if it is still random and unique. A 16-character password drawn at random from letters, digits and symbols is far beyond brute-force reach; the danger of a cap is not the cap itself but users responding to it with a memorable password. Keep the randomness, keep it unique to that site, and add a second factor where the site offers one.

Should I just add a number to a rejected password and try again?
Only if the rejection was about a missing character type. If the password was rejected for appearing in a breach, tweaking it is the worst response — the tweaked version is usually one guess away from the breached original. Generate a completely new password instead.

My password works on the website but not in the app (or the reverse). Why?
Different code paths enforcing different rules — one trims spaces, the other does not, or one truncates to a maximum the other ignores. Reset the password to one that satisfies the stricter of the two paths (no leading or trailing spaces, under the shorter cap), then test both paths before trusting it.

Why do some sites ban spaces or certain symbols in passwords?
Usually because of how their own input handling or legacy systems treat those characters, not because the characters are unsafe in a password. Current guidance is to allow all characters including whitespace — but until a site follows it, generate within its allowed set and add length to compensate.