You go from a production stack trace to the responsible line without a debugger attached by pasting the trace into Atlas and having the read tool open each frame's file at the reported offset. A stack trace is a list of file:line pairs, which is exactly what Atlas's read tool consumes. Atlas then greps for the error message string to find where it is constructed, uses the lsp tool's findReferences operation on the failing function to see which callers can reach it with the bad input, and fixes the responsible line with edit.
How do I debug a production stack trace without a debugger?
Atlas turns a production stack trace into a fix without attaching a debugger, using 4 tools: read, grep, lsp, and edit. A stack trace is a list of file:line pairs, which is exactly what Atlas's read tool consumes, so Atlas opens each frame at its offset and reconstructs the path from there.
Production failures rarely come with a debugger session attached. What they come with is a stack trace, and a stack trace is structured data: a sequence of file paths and line numbers. Atlas consumes exactly that. The read tool opens each frame at its reported offset, so the code that was actually executing is in context rather than a reconstruction of it. grep then finds the callers and the error construction the trace does not show, and the lsp tool supplies the reference graph. The trace is treated as evidence to be verified, not as a conclusion.
What if the stack trace line numbers do not match my code?
Atlas validates stack trace offsets against the current file, so a trace and a source tree from 2 different builds fail loudly instead of quietly. If the read tool reports Offset <n> is out of range for this file, re-read the file from the top before trusting any line number in that trace, because every frame in it is now suspect.
The quietest way to waste an afternoon on a runtime bug is to trace a stack from last week's build against this week's source. Line numbers drift, and a frame pointing at line 412 now points at a blank line or, worse, at plausible but unrelated code. Atlas's read tool validates the offset against the current file, so a stale trace fails loudly with Offset <n> is out of range for this file rather than pointing at the wrong code. The correct response is to stop trusting the line numbers, re-read the file from the top, and locate the frame by symbol name instead.
How do I find where an error message is constructed?
Atlas greps for the error message string to find where the error is constructed, which is usually more informative than frame 1 of the stack trace. The top frame shows where the failure surfaced, while the construction site shows the condition that decided the input was invalid, which is the actual diagnosis.
Stack traces mislead by putting the most visible frame on top. The throw site inside a validation helper or a serialization library tells you very little about why your data was wrong. Atlas greps the repository for the literal error message string, which lands directly on the code that builds the error, and reading the surrounding branch shows the precondition that failed. Atlas's grep tool takes a real regex plus include and path filters and runs through ripgrep, so scoping the search away from vendored dependencies is a parameter rather than a chore.
How do I find which callers can reach a failing function?
Atlas runs the lsp tool's findReferences operation on the failing function to see which callers can reach it with the bad input. A stack trace shows 1 path that failed, while findReferences shows every path that exists, which is how you tell whether the fix belongs in the function or in one specific caller.
The stack trace answers what happened once. The question that actually determines the fix is what can happen. Atlas answers it with the lsp tool's findReferences operation, which asks the language server for every callsite of the failing function. Reading those callsites tells you whether one caller is uniquely capable of passing the bad input, in which case the caller is the bug, or whether many callers could, in which case the function needs to defend itself. Atlas reads git branches, status, and diffs, so a recently changed caller is easy to correlate with a recently appeared trace.
Where does the human approve when Atlas fixes a runtime bug?
Atlas computes a unified diff for every file edit and surfaces it for approval before writing, so the 1 human approval point when fixing a runtime bug is the diff. Reading the trace frames, grepping for the error string, and running the lsp tool are read-only, permission-gated tool calls that change nothing.
The tracing phase of this workflow does not touch the repository. read opens the frames, grep locates the error construction, and the lsp tool's findReferences operation enumerates callers, and every one of those calls is permission-gated against allow, ask, and deny rules before it runs. The change comes at the end, when the edit tool fixes the responsible line, and that is where the unified diff appears for approval. Atlas snapshots file changes as git patches so edits can be diffed and rolled back, which matters when a fix is being made against a failure you could not reproduce locally.
How do I stop the same runtime bug from coming back?
Atlas fixes the responsible line with the edit tool and adds a regression test, which ends the workflow with 2 artifacts rather than 1. A production stack trace fixed without a test is a bug that returns in a future release with nobody watching for it, so the regression test is part of the workflow.
Tracing a runtime bug ends with two artifacts, not one. The first is the fix, applied with the edit tool to the line the trace, the grep, and the lsp tool's findReferences operation jointly identified. The second is a regression test that asserts the previously failing condition now behaves correctly. The test is what converts a one-time production incident into a permanent guarantee. Without it, the next refactor of that call path can reintroduce the exact same failure, and the next place you will hear about it is the next production stack trace.
Step by step
- 01Paste the stack trace into Atlas and have the read tool open each frame's file at the reported offset. A stack trace is a list of file:line pairs, which is exactly what read consumes.
- 02If read reports Offset <n> is out of range for this file, the trace came from a different build. Re-read the file from the top before trusting any line number in that trace.
- 03Grep for the error message string to find where the error is constructed, which is usually more informative than the top frame of the trace.
- 04Use the lsp tool's findReferences operation on the failing function to see every caller that can reach it with the bad input, not just the one path the trace recorded.
- 05Read the callers to decide whether the defect belongs in the function or in a specific caller passing bad input.
- 06Fix the responsible line with the edit tool. Atlas computes a unified diff for every file edit and surfaces it for approval before writing.
- 07Add a regression test so the trace cannot recur silently in a future release.
Frequently asked questions
- how to debug a production stack trace without reproducing it locally
- Paste the trace into Atlas. A stack trace is a list of file:line pairs, which is exactly what the read tool consumes, so Atlas opens each frame at its offset, greps for the error string, and traces callers with the lsp tool.
- why do stack trace line numbers not match my source code
- The trace came from a different build. Atlas validates offsets against the current file, so read reports Offset <n> is out of range for this file rather than silently showing you the wrong lines. Re-read the file from the top.
- where should I look first in a stack trace
- Not the top frame. Atlas greps for the error message string to find where the error is constructed, because the construction site shows the condition that failed, while the top frame often just shows a generic throw inside a helper.
- how do I find every caller that could trigger a runtime error
- Run the lsp tool's findReferences operation on the failing function. The stack trace records one path that failed; findReferences enumerates every path that exists, which decides whether the fix belongs in the function or in a caller.
- can an AI agent read a stack trace and find the bug
- Yes. Atlas reads each frame at its reported offset, greps for the error message string, walks callers with the lsp tool, and proposes a fix with edit, which arrives as a unified diff you approve before it is written.
- does Atlas change my code while investigating a stack trace
- No. Reading frames with read, searching with grep, and running the lsp tool's findReferences operation are all read-only. The only change is the fix, and Atlas computes a unified diff for it and surfaces it for approval before writing.
- should I write a test after fixing a production bug
- Yes. The Atlas workflow ends by fixing the responsible line with edit and adding a regression test, so the trace cannot recur silently the next time that call path is refactored.
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