how do I find duplicate code in a C# solution when the copies have different variable names

Ask Atlas's codebase_search for the behavior rather than the exact text. Duplication is a semantic problem, and codebase_search surfaces near-duplicate C# implementations that grep would miss because the copies were renamed. Atlas retrieves whole methods, since it indexes code by AST declarations using tree-sitter.

why does Atlas use apply_patch instead of a single edit for a C# refactor

One patch per .cs file means each call site swap is independently reviewable and revertible. A single large edit across 8 C# files gives you one all-or-nothing approval, while 8 patches let you catch the one swap that changed an exception path.

how do I know the C# refactor did not break behavior

Atlas runs xUnit via dotnet test through bash after every apply_patch rather than once at the end, so a failing suite points at the specific file that just changed. Atlas then greps for any surviving copy of the duplicated logic to confirm the extraction is complete.

does Atlas work with dotnet solutions and NuGet

Yes. The documented C# setup is to run atlas in a solution with a .csproj or .sln, let Atlas read your namespaces, project references, and NuGet packages, and ask Atlas to add xUnit tests or refactor async code, reviewing the diff before dotnet build.

what C# formatter does Atlas run after a refactor

Atlas runs dotnet format over the .cs files it touched, so the diff a reviewer sees is the helper extraction rather than whitespace churn. Formatting runs after xUnit via dotnet test is green, not before.

can I review a C# helper extraction plan before Atlas changes any files

Yes. Atlas drafts a plan in a read-only plan agent and asks before switching to a build agent, so you can have Atlas map the full duplicate set across the solution and approve the merge proposal before a single .cs file is touched.

how do I undo a bad C# refactor made by an AI agent

Atlas snapshots file changes as git patches so edits can be diffed and rolled back. Because each call site swap is a separate apply_patch, you revert the one bad swap without unwinding the good ones, then re-run xUnit via dotnet test.

Extract a Shared Helper from Duplicated C# Code with Atlas (2026)

To extract a shared helper from duplicated C# code with Atlas, you ask codebase_search for the behavior rather than the exact text, because duplication is a semantic problem and the copies almost always differ in variable names. Atlas surfaces the near-duplicate implementations that grep would miss, reads each one to confirm they are genuinely equivalent, creates the new helper class with write, and swaps each copy for a call with apply_patch, one file per patch. xUnit via dotnet test runs after every swap, and dotnet format normalizes the result.

How do I find duplicated logic in a C# solution when the copies differ?

Atlas finds duplicated C# logic with codebase_search, which retrieves by meaning rather than by text. Duplication is a semantic problem in 2026: 2 copies of the same retry loop in OrderService.cs and InvoiceService.cs will use different variable names, so grep returns zero hits while codebase_search returns both.

The reason grep fails at deduplication in C# is that copy-paste is never literal. A developer copies a validation block from Services/OrderService.cs into Services/InvoiceService.cs, renames order to invoice, swaps an int for a Guid, and the two are now textually distinct and semantically identical. Atlas asks codebase_search for the behavior (not the exact code) to surface near-duplicate implementations that grep would miss. Atlas searches code with hybrid semantic and keyword retrieval fused by reciprocal rank fusion, and Atlas indexes code by AST declarations using tree-sitter, not blind line windows, so each hit comes back as a whole C# method rather than an arbitrary window of lines. That gives you the full method body of both copies side by side, which is what you need to judge whether they can actually collapse into one helper.

How does Atlas confirm two C# methods are really duplicates before merging them?

Atlas reads each codebase_search hit in full and confirms the C# copies are genuinely equivalent before collapsing them. Two methods that look alike can differ in one null check or one exception type, and merging them anyway is how a refactor in a .NET solution turns into a production incident in 2026.

Confirmation is a separate step from discovery, and Atlas keeps it that way. After codebase_search surfaces candidates in a C# solution, Atlas uses read to open each hit and compare them line by line: does OrderService.cs swallow the exception that InvoiceService.cs rethrows, does one variant apply a CancellationToken the other ignores, does one use async/await while its twin blocks. Only when the copies are genuinely equivalent does Atlas propose the shared helper. Atlas drafts a plan in a read-only plan agent and asks before switching to a build agent, so on a large .NET codebase you can have Atlas map the whole duplicate set, review the merge proposal, and approve it before a single .cs file changes. That read-then-decide ordering is the guardrail against a merge that quietly changes behavior.

How does Atlas create the shared C# helper class?

Atlas creates the shared C# helper with the write tool, which shows the full diff in the permission prompt before the file is created. That is step 3 of the documented refactor: a new file such as Services/Shared/RetryHelper.cs appears as a reviewable diff, and any NuGet package it references is pulled in only with your approval.

Atlas creates the shared helper with write, and write is not a silent operation: it shows the full diff in the permission prompt before the file is created. In a C# solution that means the new class, its namespace, its using directives, and its signature are all in front of you before it exists on disk. Atlas writes the helper against the real signatures it read from the duplicate call sites, so the parameter list matches what the callers actually pass rather than an idealized version. If the helper needs a package, that dependency goes through NuGet, and the project reference change is visible in the .csproj diff. Every Atlas tool call is permission-gated against allow, ask, and deny rules before it runs, so the file creation, the .csproj edit, and the subsequent dotnet build are each an approved action.

Why does Atlas use apply_patch for each C# callsite instead of one big edit?

Atlas replaces each duplicated C# block with a call to the new helper using apply_patch, one file per patch, so each swap is independently reviewable and revertible. Swapping 8 call sites as one giant edit gives you one all-or-nothing approval; 8 patches give you 8 chances to catch a mistake.

Granularity is the safety mechanism. Atlas replaces each duplicate with a call using apply_patch, one file per patch, so the change to Services/OrderService.cs is a separate reviewable unit from the change to Services/InvoiceService.cs. If the seventh swap subtly changes an exception path, you see it in that patch alone rather than buried in a 400-line diff. Atlas runs the suite with bash after every swap, so xUnit via dotnet test is the gate between one file and the next, not a single check at the end. Atlas snapshots file changes as git patches so edits can be diffed and rolled back, which means a bad swap in a .NET project is reverted in one step without unwinding the six good ones. The final move is a grep for any surviving copy of the duplicated logic, proving the extraction actually finished.

How do I verify the C# refactor did not change behavior?

Atlas verifies a C# helper extraction by running xUnit via dotnet test with bash after every apply_patch, not once at the end. In a .NET solution with 300 tests, running the suite after each of 8 swaps tells you exactly which swap broke something, instead of leaving you to bisect.

Verification for a C# extraction happens per swap. Atlas runs the suite with bash after every apply_patch, so xUnit via dotnet test either stays green or fails immediately after the specific file that broke it. That is a far cheaper signal than a single run at the end. Atlas finishes by grepping for any surviving copy of the duplicated logic, which catches the call site that codebase_search ranked ninth and nobody looked at. dotnet format then normalizes the touched .cs files so the diff a reviewer sees is the extraction, not whitespace. Atlas reads git branches, status, and diffs, and can stage and create commits on your behalf, so the finished refactor lands as a commit whose message names the helper and whose diff contains the new class plus one call swap per file, with xUnit via dotnet test green throughout.

Step by step

01Run atlas in a solution with a .csproj or .sln so Atlas can read your namespaces, project references, and NuGet packages.
02Ask codebase_search for the behavior (not the exact code) to surface near-duplicate C# implementations that grep would miss because the copies renamed their variables.
03Read each hit with the read tool and confirm the C# copies are genuinely equivalent, checking null handling, exception types, and async/await differences before collapsing them.
04Record the baseline: run xUnit via dotnet test through bash and confirm the suite is green before any .cs file changes.
05Create the shared helper (for example Services/Shared/RetryHelper.cs) with the write tool, which shows the full diff in the permission prompt before the file is created.
06Replace each duplicate with a call to the helper using apply_patch, one file per patch, so each swap is independently reviewable and revertible.
07Run xUnit via dotnet test with bash after every swap, not once at the end, so a broken swap is attributed to the file that broke it.
08Grep for any surviving copy of the duplicated logic to prove the extraction actually finished across the solution.
09Run dotnet format over the touched .cs files, then have Atlas stage and commit the refactor.

Frequently asked questions

how do I find duplicate code in a C# solution when the copies have different variable names: Ask Atlas's codebase_search for the behavior rather than the exact text. Duplication is a semantic problem, and codebase_search surfaces near-duplicate C# implementations that grep would miss because the copies were renamed. Atlas retrieves whole methods, since it indexes code by AST declarations using tree-sitter.
can an AI agent extract a shared helper across multiple C# files safely: Atlas creates the helper with write, which shows the full diff in the permission prompt, then replaces each duplicate with a call using apply_patch, one file per patch. Each swap is independently reviewable and revertible, and xUnit via dotnet test runs after every one.
why does Atlas use apply_patch instead of a single edit for a C# refactor: One patch per .cs file means each call site swap is independently reviewable and revertible. A single large edit across 8 C# files gives you one all-or-nothing approval, while 8 patches let you catch the one swap that changed an exception path.
how do I know the C# refactor did not break behavior: Atlas runs xUnit via dotnet test through bash after every apply_patch rather than once at the end, so a failing suite points at the specific file that just changed. Atlas then greps for any surviving copy of the duplicated logic to confirm the extraction is complete.
does Atlas work with dotnet solutions and NuGet: Yes. The documented C# setup is to run atlas in a solution with a .csproj or .sln, let Atlas read your namespaces, project references, and NuGet packages, and ask Atlas to add xUnit tests or refactor async code, reviewing the diff before dotnet build.
what C# formatter does Atlas run after a refactor: Atlas runs dotnet format over the .cs files it touched, so the diff a reviewer sees is the helper extraction rather than whitespace churn. Formatting runs after xUnit via dotnet test is green, not before.
can I review a C# helper extraction plan before Atlas changes any files: Yes. Atlas drafts a plan in a read-only plan agent and asks before switching to a build agent, so you can have Atlas map the full duplicate set across the solution and approve the merge proposal before a single .cs file is touched.
how do I undo a bad C# refactor made by an AI agent: Atlas snapshots file changes as git patches so edits can be diffed and rolled back. Because each call site swap is a separate apply_patch, you revert the one bad swap without unwinding the good ones, then re-run xUnit via dotnet test.

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