# Run Atlas Headless in CI for Swift Projects in 2026

> Swift developers can run Atlas headless in CI using `atlas run --format json` to automate tasks and receive machine-readable output for their Swift projects.

Swift developers in 2026 can run Atlas headless in CI pipelines by invoking the `atlas run` command with a specific prompt, enabling non-interactive sessions that integrate direct with the Swift Package Manager and XCTest via `swift test`. This approach allows for automated code modifications, such as adding XCTest cases or adopting async/await, with machine-readable output for subsequent pipeline steps.

## Key takeaways

- Atlas runs headless in Swift CI using `atlas run` for non-interactive, prompt-driven automation.
- Machine-readable output is available via `atlas run --format json` for programmatic parsing in Swift pipelines.
- Pre-approve Atlas tools like `read`, `edit`, and `bash` to ensure smooth headless operations on Swift code.
- Atlas indexes Swift code by AST declarations, understanding `Package.swift` and Swift Package Manager structure.
- Resume or fork Atlas sessions with `--continue` or `--fork` for efficient multi-stage Swift CI workflows.
- Atlas can generate XCTest cases and refactor Swift code, with changes presented as unified diffs for approval.

## How to Run Atlas Headless in a Swift CI Pipeline

In 2026, running Atlas headless in a Swift CI pipeline involves invoking `atlas run` with specific arguments to execute a single prompt and exit upon session idle. This non-interactive mode is ideal for automating tasks like generating new XCTest cases or refactoring Swift code within your continuous integration environment.

To run Atlas headless within a Swift CI pipeline, you initiate an Atlas session using the `atlas run` command. This command is designed for non-interactive execution, accepting a single prompt as an argument. For instance, a Swift developer might prompt Atlas to "Add a new XCTest case to `MyFeatureTests.swift` for the `calculateTotal` function." Atlas will then process this prompt, leveraging its understanding of Swift syntax and the project's `Package.swift` structure. The session concludes automatically when Atlas determines the task is complete or the session becomes idle, making it perfect for automated workflows where human intervention is not possible. This ensures that your Swift codebase, managed by Swift Package Manager, can benefit from Atlas's capabilities without requiring a terminal-native TUI.

## Getting Machine-Readable Output from Atlas in Swift CI

For Swift CI pipelines that require programmatic parsing of Atlas's activity, the `--format json` flag is indispensable, providing a structured event stream rather than human-readable prose. This feature, available in 2026, ensures that subsequent steps in your pipeline can reliably consume and act upon Atlas's output, such as generated diffs or tool calls.

When integrating Atlas into a Swift CI pipeline, obtaining machine-readable output is crucial for automating subsequent steps. By appending `--format json` to your `atlas run` command, Atlas will stream its events to stdout as a raw JSON array. This structured output includes details about every action Atlas takes, from its initial plan drafted by the read-only plan agent to the unified diffs computed for every file edit. A Swift pipeline step can then parse this JSON to, for example, automatically review proposed changes to `Package.swift` or Swift source files, or to log specific tool calls made by Atlas, such as `bash` commands or `edit` operations. This allows for robust automation, where the CI system can programmatically approve or reject Atlas's suggested modifications to your Swift project, ensuring compliance with `swift-format` or other coding standards.

## Configuring Atlas Permissions for Headless Swift Operations

Headless Atlas runs in 2026 require pre-approved tool permissions, as there is no interactive user to respond to 'ask' prompts. Swift developers must configure a permission policy that explicitly allows tools like `read`, `edit`, `bash`, and `todowrite` to operate on their Swift codebase, preventing pipeline stalls.

A critical aspect of running Atlas headless in a Swift CI environment is managing tool permissions. Since a headless session lacks an interactive user, Atlas cannot prompt for approval when it needs to use a tool. Therefore, Swift developers must pre-configure a permission policy that explicitly allows the necessary tools. For typical Swift development tasks, this includes granting permission to `read` files (e.g., Swift source files, `Package.swift`), `edit` files (to modify code or add XCTest cases), `bash` (for executing commands like `swift test` or `swift-format`), and `todowrite` (for creating temporary files or notes). Without these pre-approvals, Atlas's build agent would halt, waiting for a response that never comes, effectively failing the CI job. This permission-gated approach ensures that Atlas only performs actions that are explicitly sanctioned within your Swift project's CI workflow.

## Resuming and Forking Atlas Sessions in Swift CI

Atlas offers robust session management in 2026, allowing Swift CI pipelines to resume or fork prior sessions using `--continue`, `--session`, or `--fork`. This capability is vital for long-running or multi-stage Swift jobs, enabling a pipeline to build upon previous Atlas runs without starting from scratch, saving compute resources and time.

For complex Swift CI workflows, Atlas provides options to manage and reuse prior sessions. If a pipeline step needs to continue work from an earlier Atlas run, the `--continue` flag can be used with a session ID. Alternatively, `--session <session_id>` allows you to specify a particular session to resume. The `--fork` option creates a new session based on an existing one, useful for parallelizing different approaches or testing variations of a task on a Swift codebase. This is particularly beneficial when Atlas is performing extensive tasks like refactoring a large Swift module or generating numerous XCTest cases across multiple targets defined in `Package.swift`. By leveraging these flags, Swift developers can design more efficient and resilient CI pipelines, ensuring that Atlas can pick up exactly where it left off, even if a previous job was interrupted or needs to be re-run with minor adjustments.

## Steps

1. Ensure your Swift project includes a `Package.swift` file, allowing Atlas to read your targets, protocols, and dependencies, which is fundamental for its code indexing via AST declarations.
2. Configure Atlas permissions in your CI environment to explicitly allow tools like `read`, `edit`, `bash`, and `todowrite` to prevent headless sessions from stalling when interacting with Swift files or running `swift test`.
3. Invoke `atlas run` in your CI script, providing a specific prompt for the task, such as `atlas run "Add XCTest cases for all public methods in 'MyService.swift'"`.
4. Include the `--format json` flag in your `atlas run` command, for example: `atlas run --format json "Refactor 'MyUtility.swift' to adopt async/await patterns"`, to get machine-readable output for subsequent pipeline steps.
5. Set the active model explicitly using the `provider/model` form, for instance: `atlas run --model github/copilot-gpt4 "Review and apply swift-format to 'Sources/MyApp/main.swift'"`.
6. Parse the JSON output from Atlas in a subsequent CI step to review the computed unified diffs for any file edits, such as changes to `Package.swift` or Swift source files, before applying them.
7. Optionally, use `atlas run --continue <session_id>` or `atlas run --fork <session_id>` to resume or build upon a previous Atlas session, especially for multi-stage Swift development tasks.
8. After Atlas completes its task and applies changes, run your Swift project's tests with `swift test` and apply formatting with `swift-format` to validate the modifications.

## FAQ

### How does Atlas integrate with Swift Package Manager in CI?

Atlas integrates with Swift Package Manager by reading your `Package.swift` file to understand targets, protocols, and dependencies. It indexes code using AST declarations, allowing it to intelligently modify Swift source files, add XCTest cases, or refactor code within your package structure, all while respecting your project's organization.

### Can Atlas generate XCTest cases automatically in a headless Swift CI pipeline?

Yes, Atlas can generate XCTest cases automatically in a headless Swift CI pipeline. By providing a prompt like "Add XCTest cases for the `MyClass` in `MyFile.swift`", Atlas will draft and propose new test methods, which can then be reviewed via its unified diff output and integrated into your project after running `swift test`.

### What Atlas tools are essential for headless Swift development in CI?

For headless Swift development in CI, essential Atlas tools include `read` (to analyze Swift files and `Package.swift`), `edit` (to modify code), `bash` (to execute commands like `swift test` or `swift-format`), and `todowrite` (for temporary notes). These must be pre-approved in your Atlas permission configuration for non-interactive runs.

### How does Atlas ensure safety when modifying Swift code in CI?

Atlas ensures safety by drafting a plan in a read-only agent first, then computing a unified diff for every proposed file edit. In a headless CI setup, this diff is surfaced in the `--format json` output, allowing your pipeline to programmatically review and approve or reject changes before they are written to your Swift codebase.

### Can Atlas apply `swift-format` automatically in a CI pipeline?

While Atlas doesn't directly *run* `swift-format` as an internal tool, it can use its `bash` tool to execute the `swift-format` command on your Swift codebase. You can prompt Atlas to "Apply `swift-format` to all Swift files" and ensure the `bash` tool is permitted, allowing it to integrate with your existing formatting workflow.

### How do I debug a failed headless Atlas run in Swift CI?

To debug a failed headless Atlas run in Swift CI, examine the `--format json` output for detailed event streams, including tool calls and errors. You can also use the `--session <session_id>` flag to resume the exact session in an interactive Atlas terminal, allowing you to inspect the state and manually step through the agent's actions.

### Does Atlas support local Ollama embeddings for Swift code indexing?

Yes, Atlas supports building its code index with local Ollama embeddings, keeping your Swift code off third-party servers. This is particularly beneficial for Swift projects with strict privacy requirements, ensuring that your proprietary code remains within your local or CI environment while still leveraging Atlas's semantic search capabilities.

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