We get a lot of Replit Agent projects through the door, probably more than any single tool apart from Cursor. That’s not a knock on Replit. Agent is genuinely good at what it’s built for: standing up a working app fast, wiring the frontend to a backend, and getting something clickable in front of a founder before lunch. The Replit Agent bugs we see aren’t random either. They cluster into a handful of predictable patterns, and once you’ve fixed fifty of these projects you can usually guess what’s broken before you even open the repo.
This one is the tool-specific companion to our breakdown of the ten most common bugs in AI-generated code, narrowed down to what Replit Agent specifically tends to get wrong. If you want the wider comparison across tools, we’ve also written about how Cursor, Bolt, and Lovable differ in what breaks and what’s worth rebuilding.
What Replit Agent gets right
Worth saying first, because it’s easy for a piece like this to read as one long complaint. Replit Agent is strong at scaffolding a full-stack app in one go: frontend, backend, database, and hosting all in the same environment, with the agent able to run commands, read logs, and iterate on errors it sees. That loop, where the agent can actually execute code and react to failures rather than just guessing, produces fewer syntax errors and dead imports than some competing tools. It’s also genuinely fast to get a working demo live, which is exactly what a founder validating an idea needs.
The trouble starts once “working demo” becomes “thing real users are putting real data into.” That’s where the same shortcuts that made the demo fast start causing problems.
The recurring problems we keep finding
Environment variables and secrets
This is the big one, and it’s the one we’d flag first if you can only check one thing. Replit’s own Secrets manager exists and works fine, but Agent doesn’t always use it. We’ve opened projects with API keys hardcoded directly into route files, database connection strings pasted straight into frontend code that ships to the browser, and Stripe secret keys sitting in a .env file that got committed to a public Repl. Once, an admin password was left as a plain string constant in a component that was rendered client-side. None of this is unique to Replit, but the specific failure mode we see there is Agent generating working code fast and treating “does it run” as the finish line, with secrets management as an afterthought it only handles if you explicitly ask.
If you want the fuller picture of what this kind of exposure can cost you, our security guide for AI-built apps goes through it in more depth.
Over-eager scaffolding
Ask Agent for a login page and it will often give you a login page, a signup page, a password reset flow, an admin dashboard, a settings panel, and three API routes you never asked for. This sounds generous until you realise nobody reviewed any of it. We regularly find entire admin panels sitting behind no authentication check at all, reachable by anyone who guesses the URL, because the agent built the feature but the founder never knew it existed to test it. The instinct to be thorough is good in a junior developer you’re supervising closely. In an agent nobody is reading the output of, it just multiplies the attack surface.
Database defaults
Replit’s built-in database options make it trivially easy to spin up storage, which is great for speed and less great for what Agent does with the defaults. We see permissive access rules left wide open, tables with no row-level restrictions so any authenticated user can read or edit any other user’s data, and schema fields with no validation at all so a form can write malformed data straight through to production. One project we fixed had a users table where the role field was a plain string with no constraint, meaning any client-side request that included "role": "admin" in its payload would have been accepted at face value. That’s not a hypothetical, someone could have escalated their own account with a browser dev tools tab open for thirty seconds.
Deployment surprises
This is the one that catches people off guard because it happens after everything felt done. Replit’s deployment step often behaves differently from the dev environment underneath it, meaning apps that ran fine while being built fail once deployed, usually around environment variables not carrying over, background jobs that only worked because the dev server happened to be always-on, or file storage that was writing to local disk and vanishes the moment the deployment restarts. We’ve had clients call us in a panic because their app “worked yesterday” and broke the moment they hit deploy, when really the underlying issue had been there the whole time, just masked by the dev environment’s more forgiving behaviour.
How severe are these, really
Not every issue here carries the same weight, and it’s worth being honest about that rather than treating every finding as a five-alarm fire. Exposed secrets and open database access are the ones we escalate immediately, because they’re exploitable the moment your app has real users and real data, not eventually, immediately. Over-eager scaffolding is a medium-severity problem on its own but becomes high severity the moment one of those unrequested admin routes has no auth in front of it, which in our experience is more often than not. Deployment surprises are usually not a security issue so much as a reliability and trust one: nothing worse for a founder’s credibility than a demo that worked in front of an investor and then silently breaks in production a week later.
How to check your own Replit project
You don’t need a computer science degree to run a first pass on this yourself, and we’ve written a broader walkthrough on reviewing AI-generated code without being a developer if you want the general version. For Replit specifically, start by opening every file in your project and searching for the words “key”, “secret”, “password”, and “token”. Anything that looks like a real credential sitting in plain text needs to move to Replit’s Secrets manager immediately, not eventually. Next, list every route and page your app actually has, including ones you didn’t explicitly ask for, and check whether each one requires a login before it does anything sensitive. Then look at your database rules directly rather than trusting that they’re fine because the app works, since “works” and “secure” are answering two different questions. Finally, deploy to a staging environment before you deploy to production, and actually click through the core flows there rather than assuming dev behaviour carries over.
If any of that turns up something you’re not sure how to fix, or you’d rather have someone else run the check, that’s fine too. Our pre-launch checklist for vibe coders is a good place to start before you go looking for outside help.
Built it on Replit and something feels off? We’ll take a look for free, get in touch and we’ll tell you honestly what needs fixing before it becomes a problem for your users.