# Audit an Elixir Repo with Parallel Subagents in 2026 using Atlas > Atlas allows Elixir developers to sweep an entire repository for problems using parallel subagents, preserving the main session's context window. Atlas enables Elixir developers in 2026 to sweep an entire repository for a class of problems without blowing the main session's context window by launching parallel subagents. These subagents, leveraging Elixir's `mix` projects and OTP applications, can independently audit specific code slices, ensuring efficient and focused analysis of your codebase. ## Key takeaways - Atlas uses parallel subagents to audit large Elixir `mix` projects and OTP applications without blowing the main session's context window. - The `explore` subagent type provides a read-only environment, ensuring Elixir code sweeps do not accidentally modify `mix.exs` or `lib` files. - Atlas integrates with Elixir's toolchain, allowing subagents to analyze `ExUnit` tests, `Mix and Hex` dependencies, and `mix format` consistency. - Every proposed change to your Elixir codebase, from `GenServer` refactors to `mix format` applications, requires explicit approval via unified diffs. - Audit findings are consolidated into a `todowrite` list, enabling systematic fixes using `atlas edit` within your Elixir development workflow. ## How Atlas Splits Elixir Repo Audits into Parallel Slices Auditing an Elixir repository with Atlas begins by defining the scope for each parallel subagent. In 2026, developers leverage Atlas to break down large `mix` projects or OTP applications into 3 or more independent slices, preventing any single subagent from exceeding context window limits while ensuring comprehensive coverage. To effectively audit a large Elixir codebase, Atlas encourages splitting the task into independent slices. This means you might assign one subagent to sweep the `lib/my_app/` directory for a specific pattern, another to `lib/my_other_app/`, and a third to `test/` files to check `ExUnit` test coverage or style. By using Atlas's `glob` tool, you can precisely define these boundaries, ensuring subagents do not overlap their work. For instance, you could instruct one subagent to focus on all `.ex` files within a specific OTP application's `lib` directory, while another targets only `mix.exs` files across the entire monorepo. This modular approach, combined with Atlas's ability to index code by AST declarations using tree-sitter, ensures that each subagent receives only the relevant code context for its assigned slice, making the audit both thorough and resource-efficient. ## Launching Read-Only Elixir Code Sweeps with Atlas Subagents To sweep an Elixir repository for problems without making unintended changes, Atlas provides the `explore` subagent type, which is deny-by-default and read-only. This ensures that when you launch 5 parallel tasks to audit different parts of your `mix` project, no subagent can modify files or run commands like `mix format` without explicit permission. When performing an audit, the primary goal is to identify issues without introducing new ones. Atlas's `task` tool, when invoked with `subagent_type explore`, creates a read-only environment for the subagent. This is ideal for sweeping Elixir codebases, as it prevents the subagent from accidentally altering `mix.exs` files, `lib` modules, or `test` suites. For example, you can launch multiple `task` calls concurrently, each targeting a different Elixir context or module group using `grep` or `glob`. An `explore` subagent might use `grep` to find deprecated function calls across `lib/my_app/**/*.ex` files, or analyze `test/my_app_test.exs` for common `ExUnit` anti-patterns. The subagent's findings are then returned to the main session, but its file dumps never enter your context, preserving your main session's focus and context window. ## Collecting and Merging Elixir Audit Findings from Parallel Tasks After launching multiple parallel subagents to audit your Elixir codebase, Atlas automatically collects each subagent's final message, providing a unified view of all findings. This process, typically involving 3 to 8 concurrent tasks, consolidates insights from various parts of your `mix` project or OTP application into a single, actionable list. Once your parallel subagents complete their read-only sweeps of the Elixir repository, Atlas efficiently gathers their conclusions. Each subagent's final message, whether it's a list of identified issues in `lib/my_app/` or suggestions for `mix.exs` dependencies, is surfaced back to your main Atlas session. If a subagent encounters an issue or is cancelled, Atlas surfaces the child's error text verbatim, providing immediate feedback. The next step is to merge these individual findings into a single, comprehensive `todowrite` list. This consolidated list allows you to review all identified problems, such as inconsistent `mix format` application, potential `ExUnit` test improvements, or outdated `Mix and Hex` dependencies, in one place before proceeding to fix them in your main session using the `edit` tool. ## Ensuring Safety and Review for Elixir Code Changes with Atlas Atlas prioritizes safety and developer control throughout the audit and remediation process for Elixir codebases. Every Atlas tool call is permission-gated against allow, ask, and deny rules, ensuring that any proposed changes, like running `mix format` or modifying a `GenServer`, are explicitly approved by you before execution. This applies to all 2026 Atlas interactions. Even when moving from audit to remediation, Atlas maintains strict control over your Elixir codebase. Before any build agent can make changes, Atlas drafts a plan in a read-only plan agent and asks for your approval. This means if an audit identifies a need to refactor a `GenServer` in `lib/my_app/worker.ex` or update a dependency in `mix.exs`, you will see the proposed plan first. Furthermore, for every file edit, Atlas computes a unified diff and surfaces it for your approval before writing. This granular control extends to running commands like `mix test` or `mix format`; Atlas will always ask for permission if a tool call is not explicitly allowed. This robust review mechanism ensures that all modifications, from minor formatting adjustments to significant `OTP application` restructuring, align with your intentions and maintain the integrity of your Elixir project. ## Fixing Elixir Code Issues with Atlas's Integrated Tools After consolidating audit findings into a `todowrite` list, Atlas empowers Elixir developers to fix identified issues directly within the main session using the `edit` tool. This streamlined workflow allows you to address problems like inconsistent `mix format` application or `ExUnit` test failures efficiently, often with just 1 or 2 commands. With a comprehensive `todowrite` list generated from your parallel subagent audits, you can now systematically address the identified issues in your Elixir project. The `edit` tool in Atlas allows you to apply fixes directly. For instance, if the audit revealed inconsistent formatting across `lib/my_app/**/*.ex` files, you could use `edit` to apply `mix format` to the affected files, reviewing the unified diff before committing. If `ExUnit` tests in `test/my_app_test.exs` were flagged for improvement, Atlas can help restructure them or add new assertions, again presenting a clear diff for your approval. Atlas also reads git branches, status, and diffs, and can stage and create commits on your behalf, making the entire fix-and-commit cycle for your Elixir codebase direct and fully auditable. You can even roll back edits using Atlas's snapshot feature, which saves file changes as git patches. ## Steps 1. Split your Elixir `mix` project or OTP application into independent slices (e.g., by directory like `lib/my_app/`, `test/`, or by specific `mix.exs` files) to define the scope for each subagent. 2. Launch multiple parallel tasks using `atlas task subagent_type explore` for read-only sweeps. For example, `atlas task 'grep -r "old_function" lib/my_app/**/*.ex'` and `atlas task 'glob "test/**/*.exs" | xargs grep "ExUnit.Assertions"'` to run concurrently. 3. Issue all `atlas task` calls together in your main session to ensure they run concurrently, leveraging Atlas's ability to fan out work to subagents in parallel background sessions. 4. Collect each subagent's final message, which Atlas surfaces automatically. Review any error text if a child task fails or is cancelled, providing immediate feedback on your Elixir codebase audit. 5. Merge the findings from all subagents into a single `todowrite` list using `atlas todowrite add 'Fix inconsistent mix format in lib/my_app/'` or similar commands based on the audit results. 6. Fix the identified issues in your Elixir codebase using `atlas edit`. For example, `atlas edit 'apply mix format to lib/my_app/module.ex'` or `atlas edit 'add ExUnit test for new GenServer behavior in test/my_app_test.exs'`, reviewing the unified diff before approval. 7. Approve the proposed changes after reviewing the unified diffs. Atlas will then write the changes to your Elixir files, ensuring full control over modifications to your `mix` project. ## FAQ ### How does Atlas prevent context window overflow when auditing a large Elixir monorepo? Atlas prevents context window overflow by launching parallel subagents, each assigned to an independent slice of your Elixir monorepo, such as a specific `mix` project directory or an OTP application. Only the subagent's conclusions, not its raw file dumps, return to the main session, preserving your context. ### Can Atlas subagents modify my Elixir code during an audit? By default, for audits, you launch `subagent_type explore` which is read-only and deny-by-default. This ensures that subagents cannot modify your Elixir code, run `mix format`, or alter `mix.exs` files without explicit permission, making the sweep safe. ### How does Atlas ensure I review all changes to my Elixir project? Atlas ensures review by drafting a plan in a read-only plan agent and asking for approval before any build agent acts. For every file edit, Atlas computes and surfaces a unified diff for your approval before writing, giving you full control over changes to your Elixir codebase. ### What Elixir tools does Atlas integrate with for auditing? Atlas integrates directly with the core Elixir toolchain. It understands `mix` projects and OTP applications, can analyze `ExUnit` tests via `mix test`, manage dependencies with `Mix and Hex`, and enforce code style using `mix format`. ### How do I consolidate findings from multiple parallel Elixir audits? Atlas automatically collects the final messages from all parallel subagents. You then merge these individual findings into a single `todowrite` list using Atlas's `todowrite` tool, providing a unified view of all identified issues across your Elixir codebase. ### Can Atlas help me fix `ExUnit` test issues in my Elixir project? Yes, after an audit identifies `ExUnit` test issues, you can use `atlas edit` to address them. Atlas can help restructure tests, add assertions, or refactor test helpers in `test/my_app_test.exs`, always presenting a unified diff for your approval before applying changes. ### Does Atlas support Elixir's `mix.exs` and `OTP application` structures? Absolutely. Atlas is designed to work direct within Elixir codebases, understanding `mix` projects and OTP applications. It can read your supervision tree, contexts, and dependencies defined in `mix.exs`, allowing for intelligent and context-aware auditing and refactoring. --- Canonical HTML: https://runatlas.sh/resources/stacks/audit-a-repo-with-parallel-subagents-in-elixir Source of truth: aeo_pages row `/resources/stacks/audit-a-repo-with-parallel-subagents-in-elixir` (segment: Stacks) (this file is generated from it, never hand-edited). Licence: Atlas is proprietary with a free core. It is not open source and there is no public source repository.