To plan a multi-file change in C# before editing, switch Atlas into its plan agent, whose description is literally Plan mode. Disallows all edit tools. Atlas is the terminal-native AI coding agent, and in plan mode its permission set denies edit for every path except the plan markdown, so research across your .csproj projects, namespaces, and NuGet references cannot accidentally turn into a write. Atlas researches with codebase_search, grep, read, and the lsp tool, writes the design into .atlas/plans/*.md, and only after you approve plan_exit does the build agent start editing and running dotnet format and dotnet test.
How do I plan a large C# refactor before changing any files?
Atlas ships a plan agent whose description is literally Plan mode. Disallows all edit tools. Switch into it before touching a C# solution in 2026 and Atlas can read every .csproj, walk the namespaces, and draft the change, while its permission set denies edit for "*" and allows writes only under .atlas/plans/*.md.
A refactor that spans a .NET solution is the case where a plan pays for itself. Renaming an interface, moving a service between projects, or replacing a synchronous call chain with async touches the .csproj project references, the using directives in every consumer, and the xUnit test projects that pin the old shape. Atlas drafts a plan in a read-only plan agent and asks before switching to a build agent, so all of that discovery happens before any file changes. The plan agent is not a convention or a prompt instruction. Its permissions deny edit for every path except the plan markdown, which is the one place plan mode can write.
What can Atlas plan mode still do in a .NET solution?
Atlas plan mode keeps all research tools allowed in a C# solution: codebase_search, grep, read, and the lsp tool. Only editing is denied. So a plan agent can enumerate every implementation of an interface across 12 projects in a .sln, follow project references, and read the NuGet packages a project depends on.
Research is the whole job in plan mode, and Atlas gives it the full read-side toolkit. codebase_search queries the semantic index, and because Atlas indexes code by AST declarations using tree-sitter, not blind line windows, a hit lands on a C# class or method declaration rather than on an arbitrary window of a 900-line file. grep runs through ripgrep with real regex plus include and path filters, which is how you find every `using Contoso.Billing;` line in a solution. The lsp tool gives the symbol graph, so findReferences on an interface method returns real callsites in the other projects rather than string matches. Nothing in that list can write, which is the point.
Where does Atlas write the plan for a C# change?
Atlas writes the plan into the allowed markdown path under .atlas/plans/*.md, the only place plan mode can write. For a C# solution in 2026 that document holds the ordered list of projects to touch, the NuGet packages to add or remove, and the xUnit test projects that need updating before dotnet test goes green.
Putting the plan on disk rather than in chat history matters for a multi-file .NET change, because the plan is the thing that gets reviewed. A colleague can read .atlas/plans and comment on the sequencing before a single .cs file moves. Good plans for C# name the concrete artifacts: which .csproj gains a ProjectReference, which namespace changes, whether the change forces a NuGet version bump, and which xUnit facts and theories assert the old behavior. Atlas can compile that list from its own research, and because the plan agent is read-only outside the plan file, drafting it carries no risk to the solution.
How does plan_exit hand off from planning to building in C#?
Atlas hands off with the plan_exit tool, and there are exactly 2 answers. Once the C# plan is written, plan_exit asks whether to switch to the build agent and start implementing. Answer Yes and the build agent takes over. Answer No and Atlas raises Question.RejectedError and keeps you refining the plan.
The handoff is an explicit gate, not a silent mode change. Answering No is a real branch: Question.RejectedError keeps the session in plan mode, so a plan you are not happy with cannot quietly become a stream of edits to your .cs files. Answering Yes moves to the build agent, which is where writes become possible. From there the ordinary safety story applies. Atlas computes a unified diff for every file edit and surfaces it for approval before writing, and Atlas snapshots file changes as git patches so edits can be diffed and rolled back. A refactor that spreads across a .sln is exactly the change you want to be able to roll back.
How do I verify a multi-file C# change after the build agent runs?
Verify a multi-file C# change with 3 commands from the .NET toolchain the solution already uses: dotnet test to run xUnit across every test project, dotnet format so the diff is about logic instead of whitespace, and dotnet build before the pull request. Atlas surfaces each unified diff for approval first.
A plan is only as good as the verification that follows it. In a C# solution, xUnit via dotnet test is the test runner, so the plan should name the test projects it expects to break and the ones it expects to stay green. NuGet is the package manager, so any dependency change belongs in the plan rather than as a surprise in the diff. dotnet format is the formatter, and running it after the build agent finishes keeps the review focused. Atlas reads git branches, status, and diffs, and can stage and create commits on your behalf, so the last step of a planned refactor can be a single reviewed commit rather than a scattered pile of edits.
Step by step
- 01Run atlas in a solution with a .csproj or .sln so the C# projects, namespaces, and NuGet references are in scope.
- 02Switch to the plan agent; its permissions deny edit for "*" and allow it only under .atlas/plans/*.md, so no .cs file can change during design.
- 03Research the C# solution with codebase_search, grep, read, and the lsp tool; all of them stay allowed in plan mode.
- 04Use the lsp tool's findReferences operation on the interface or method you are changing to enumerate every callsite across the .sln before deciding on a sequence.
- 05Write the plan into the allowed plan markdown path, naming each .csproj to touch, each NuGet package to add or bump, and each xUnit test project that will need updating.
- 06Call plan_exit; it asks Plan at <path> is complete. Would you like to switch to the build agent and start implementing?
- 07Answer Yes to hand off to the build agent, or No to raise Question.RejectedError and keep refining the C# plan.
- 08Review each unified diff the build agent surfaces before it writes, then run xUnit via dotnet test and dotnet format before dotnet build.
Frequently asked questions
- how to plan a big refactor in a dotnet solution with an ai agent
- Switch Atlas to its plan agent, which disallows all edit tools. Research with codebase_search, grep, read, and the lsp tool, write the plan to .atlas/plans/*.md, then call plan_exit to hand off to the build agent.
- can atlas read my c# code without editing it
- Yes. Atlas's plan agent permission set denies edit for every path except the plan markdown, so it can read every .csproj, namespace, and NuGet reference in your solution while remaining unable to write a .cs file.
- what is plan_exit in atlas
- plan_exit is the tool that ends planning. It asks whether to switch to the build agent and start implementing. Answering No raises Question.RejectedError and keeps the session in plan mode.
- how do i find every implementation of an interface in a large c# solution
- Use the lsp tool's findReferences operation in Atlas. It reads the symbol graph rather than matching strings, so implementations and callsites across separate .csproj projects all appear.
- does atlas run dotnet test after a refactor
- Atlas can run xUnit via dotnet test and dotnet format after the build agent applies the plan. Atlas computes a unified diff for every file edit and surfaces it for approval before writing.
- how do i stop an ai coding agent from editing files while it researches
- Use plan mode. Every Atlas tool call is permission-gated against allow, ask, and deny rules before it runs, and the plan agent's rules deny edit for "*" outside .atlas/plans/*.md.
- can i roll back a multi-file c# change made by an ai agent
- Yes. Atlas snapshots file changes as git patches so edits can be diffed and rolled back, and Atlas reads git branches, status, and diffs before proposing changes.
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