Duplicate Code Finder — Detect Repeated Lines
Find repeated lines and code blocks in source code to identify DRY violations and refactoring opportunities.
How it works
- 1Paste or type your text in the input field
- 2Click "Find Duplicates" — processing happens in your browser
- 3Copy the result or download as a text file
What to do next
About Duplicate Code Finder
Duplicate Code Finder handles a focused step in the modern developer utility workflow. Find repeated lines and code blocks in source code to identify DRY violations and refactoring opportunities. The page loads with the upload area, controls and result panel all visible at once, so the path from "I have a file" to "I have the result" is one screen long.
Typical users of Duplicate Code Finder include devops engineers crafting one-liners, backend developers inspecting requests and QA engineers writing repro cases. The thread connecting all of them is the same: a focused developer utility task that fits cleanly into a browser tab and benefits from a tool with sensible defaults and minimal setup.
Duplicate Code Finder runs the entire transformation inside your browser. The file is read by JavaScript running in the page, processed in-memory by standard browser APIs, and written back as a download. The browser is the runtime; the page is the interface. You can confirm what the tool does by opening the developer-tools Network tab during a run — the only requests are for the page's own static assets.
Architecturally, Duplicate Code Finder is a single-page client. The processing layer is standard browser APIs; the UI is a thin React shell on top. Inputs flow through the engine and the output is returned to the browser as a Blob you can save or copy. The 0 MB cap is the only hard limit and it exists to keep memory usage stable on every device.
Most people land on Duplicate Code Finder via a search at the moment they actually need the tool. That shapes the design: the page is a single screen with the input on one side, the controls in the middle, and the result on the other, so a first-time visitor can complete the job without reading documentation.
If your task needs more than one step, chain Duplicate Code Finder with Code Complexity Estimator, Dead Code Detector, and Code Line Counter. Each tool produces output that is a clean input to the next, so multi-step workflows are just a matter of opening the next tool in a new tab and continuing.
The output handed back by Duplicate Code Finder is the output file. If you would prefer to keep the result in the browser instead of downloading it, you can copy it from the result panel and paste it directly into another tab — useful when the next tool in your workflow expects pasted text rather than a file.
The hard constraints are easy to remember. Maximum input: 0 MB. Multiple files per run: no — one input at a time, by design, to keep results predictable. The same controls apply on every run.
Duplicate Code Finder is built around steady iteration on a small set of options rather than feature creep. Every additional setting attracts a slightly different audience, but a long settings panel makes the common case slower for everyone. The current controls reflect what users of the tool actually use.
A short note on how Duplicate Code Finder came to look the way it does: every iteration started by watching how someone unfamiliar with the tool actually used it, then removing whatever got in their way. That is why the upload area dominates the screen, the run button is bigger than the secondary controls, and the result panel is unmissable when the job finishes.
Tips from users who reach for Duplicate Code Finder regularly: process one input first to confirm the settings produce what you expect before committing to a batch; treat the page as the working surface and avoid leaving large jobs running in a backgrounded tab where the browser may throttle JavaScript; and if a particular file fails, check whether the source is intact by opening it in its native viewer — most "tool errors" are actually input errors.
When something goes wrong, the cause is usually one of three things: a malformed input, a browser that is out of memory, or a corporate proxy that is interfering with the page's static assets. The first two are easy to diagnose; the third typically requires asking your IT team to allow standard browser APIs to load.
If you also use a command-line tool for duplicate code finder, Duplicate Code Finder is a convenient alternative for the times you are on a different machine or helping someone who is not comfortable in a terminal. The output is a standard file in the format documented above.
Duplicate Code Finder is intentionally narrow in scope so the common case is fast and the result is predictable. If you ever need a variation it does not cover, browse the rest of the catalog — there is a good chance an adjacent tool already exists, and switching between tools is just a matter of opening another tab.
How it works
- 1Reach the Duplicate Code Finder page in your browser to begin.
- 2Select the developer file you want to process — drag-and-drop and the file picker both work.
- 3Pick any non-default settings you need. Most users leave the defaults alone for the first run and only revisit if the result needs tuning.
- 4Click to start the job. The engine (standard browser APIs) processes the input in the page; you can watch the progress indicator until it completes.
- 5Grab the output as soon as the run completes. You can also copy the result instead of downloading if the next tool in your workflow accepts pasted input.
- 6Re-run with different settings as often as you want. Each run produces a fresh output and the original file on disk is never modified.
Common use cases
- Inspect a regex against a test string before committing it using Duplicate Code Finder.
- Compare two API responses to spot a regression.
- Validate a config blob before pushing to staging.
- Hash a string for a quick reproducibility check.
- Inspect a payload during local development without writing a script.
- Decode a token to confirm its claims during a debugging session.
- Generate boilerplate from a single specification line.
- Convert between data formats while wiring up an integration.
FAQ
What counts as a duplicate?
Lines that appear more than once (after trimming whitespace) and meet the minimum length threshold.
Are trivial lines excluded?
Yes — single braces, empty lines, closing parentheses, and pure comment lines are excluded from duplicate detection.
Can I adjust the minimum length?
Yes — choose 5, 10, 20, or 30 characters as the minimum line length for duplicate detection.
Does it find block-level duplicates?
Currently it finds line-level duplicates. Consecutive duplicate lines often indicate repeated blocks.
What does DRY mean?
Don't Repeat Yourself — a principle suggesting every piece of knowledge should have a single source of truth.
Is my code private?
Yes — analysis runs entirely in your browser.
Does Duplicate Code Finder have an API?
Duplicate Code Finder is a browser-only tool by design and does not expose a hosted API. The reason is the same as the privacy story: there is no Favtoo backend doing the work, so there is no service to call. If you need to script the same transformation, the underlying engine (standard browser APIs) is open-source and can be used directly from your own code.
Does Duplicate Code Finder work with screen readers?
Duplicate Code Finder uses native HTML controls wherever possible, which means keyboard navigation, focus rings, and screen-reader labels work the way the platform expects. The drop zone accepts files via the keyboard-accessible file picker as well as drag-and-drop, and result downloads use standard browser download flows. If you spot an accessibility gap, Favtoo treats it as a bug worth fixing.
What is the maximum file size for Duplicate Code Finder?
Inputs are capped at 0 MB per file, which keeps memory usage stable across phones, tablets and older laptops. You can run Duplicate Code Finder as often as you need; every run produces a full-quality result.
Will Duplicate Code Finder keep working if my Wi-Fi drops mid-task?
Once the page is loaded, Duplicate Code Finder can complete jobs without an active internet connection — the engine is bundled with the page, so there is no per-job network call. The initial page load does require a connection (to fetch the static assets), but after that you can disconnect entirely and the tool will still work. This is a side-effect of the local-first architecture, not a deliberate "offline mode" feature.
Is the source for Duplicate Code Finder available?
Duplicate Code Finder is a static page running an open-source engine in your browser, so a typical corporate firewall does not get in the way as long as it allows JavaScript to load from Favtoo. For teams that need to host it themselves on an internal network, the underlying engine (standard browser APIs) is open-source and can be packaged into a private build with the same behaviour. Reach out via the Contact page if that is something you are exploring.
What does the error message in Duplicate Code Finder mean?
Failures usually fall into one of three buckets: the input is in an unsupported format, the input is over the size cap, or the input is structurally malformed (a truncated download, a partial export, or a stream the engine does not recognise). The first two are easy to confirm — check that your file is in a supported format and that it is below 0 MB. For the third, opening the file in its native viewer first is the fastest way to confirm the source is intact.
How is Duplicate Code Finder different from desktop apps that do the same thing?
Desktop apps usually have more advanced features but require installation, maintenance and (often) a licence. Paid online tools are convenient but route your file through their servers and gate downloads behind accounts. Duplicate Code Finder sits in between: free, instant, and private, but intentionally narrow in scope. For one-off jobs and the common developer utility operations, it is usually the lowest-friction choice; for highly specialised work, a dedicated app is still the right answer.
Does Favtoo keep a copy of files I process with Duplicate Code Finder?
Favtoo keeps no copy of your file because Favtoo never receives your file. Duplicate Code Finder runs entirely in your browser, the input is held only in your tab's memory, and closing the tab discards it. There is no opt-in cloud history, no "recent jobs" panel synced to an account, and no server-side retention to configure — the architecture simply has nowhere for your file to be stored.
How fast is Duplicate Code Finder?
Most jobs finish in seconds. Speed scales with input size and with how many CPU cycles your browser tab has available — the engine runs in your browser, so it shares resources with whatever else you have open. For inputs near the 0 MB ceiling, expect anywhere from a few seconds to roughly a minute on a typical laptop. Closing other heavy tabs noticeably speeds things up.