gemini-cli-headless 4.0.2

A resilient, zero-dependency Python wrapper for the official Google Gemini Node.js CLI.

Gemini CLI Headless

gemini-cli-headless is a Python-based wrapper for the Gemini CLI. It provides a secure, programmatically controllable execution environment designed for autonomous agents, automated workflows, and complex data extraction.

Quick Start

Prerequisite: Both usage and testing of this library require a valid Google Gemini API key. Ensure it is available in your environment before running any code:

# Windows
$env:GEMINI_API_KEY="your-api-key"

# Linux / macOS
export GEMINI_API_KEY="your-api-key"

Alternatively, you can pass it directly to the function using the api_key argument. The wrapper will fail with a clear ValueError if the key is completely missing.

Example 1: The Secure Coding Agent Allow the agent to edit files, but strictly confine it to a specific directory and whitelist exactly which shell commands it can run.

import os
from gemini_cli_headless import run_gemini_cli_headless

project_root = os.path.abspath("./my_project")

session = run_gemini_cli_headless(
    prompt="Refactor the authentication logic.",
    cwd=project_root,
    # 1. Physical Tool Sandbox
    allowed_tools=["read_file", "replace", "run_shell_command"],
    # 2. Physical Path Sandbox
    allowed_paths=[project_root], 
    # 3. Surgical Shell Sandbox
    allowed_commands=["npm test", "git status"] 
)

print(session.text)

Example 2: The Strict Data Bot (No Tools, Custom Persona) Wipe the default Software Engineer identity entirely. Prevent the model from using any tools, ensuring it only processes the text provided.

from gemini_cli_headless import run_gemini_cli_headless

strict_persona = """
You are a DATA_BOT. You do not write code. 
You extract names from text and return them as a JSON array.
No preamble, no explanation, no tools.
"""

session = run_gemini_cli_headless(
    prompt="Hello, my name is Alice and I work with Bob.",
    system_instruction_override=strict_persona,
    allowed_tools=[], # Physically disable all tool access
)

print(session.text)
# Output: ["Alice", "Bob"]

Why this library?

If you try to orchestrate the official Gemini CLI headlessly out-of-the-box, you quickly realize it is a disaster waiting to happen. The raw CLI is optimized for interactive developer usage, not programmatic control.

When building workflows, developers face enormous pain points that gemini-cli-headless solves:

1. The Persona Problem & Model Identity The CLI has a hardcoded "Software Engineer" identity. Try asking it to simply extract JSON from a document, and it will often refuse or start explaining its engineering credentials.

• Our Solution: We implemented the system_instruction_override parameter to completely wipe the agent's mind and replace it with your instructions. Read about how we handle model paranoia in Controlling the Agent's Mind.

2. Inconsistent Sandboxing & Dangerous Defaults Headless mode requires using --raw-output and the --yolo flag. By default, the agent has free rein over your filesystem and shell. Trying to restrict the agent to a specific folder or a specific set of tools via CLI flags is extremely difficult and non-transparent.

• Our Solution: We directly manipulate the undocumented internal policy engine to create a "Zero-Trust" environment. Dive into the deep technical details of Enforcing the Sandbox (The Security Kernel) and Securing the Filesystem (Path Defenses).

3. Hierarchical Context Pollution If you run the raw CLI inside your project, it stealthily searches parent directories for GEMINI.md files. Your headless bot's behavior will mysteriously change depending on which folder it runs in because it's secretly inheriting external project rules.

• Our Solution: We built a surgical environment trick (isolate_from_hierarchical_pollution=True) that forces the CLI into a clean room, guaranteeing your persona remains pure. Understand our overarching philosophy in How We Tamed the Engine (Architecture Overview).

We have done our best not only to provide clear controls for these challenges, but also to create a suite of smart edge-case tests to verify this safety. You can learn about our trace auditing in How We Test. For detailed API references and advanced configuration options, also take a look at the Usage & Examples page.

Recommended Models

For the best balance of speed, cost, and obedience to the strict sandboxing rules, we strongly recommend using the following specific models:

1. gemini-3.1-flash-lite-preview: The best choice for high-volume, tool-restricted tasks and data extraction. Extremely fast.
2. gemini-3-flash-preview: Excellent middle ground for agents that need to use basic tools (read/write files) rapidly.
3. gemini-3.1-pro-preview: Use this when the task requires deep reasoning or complex, multi-step shell orchestrations.

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⚠️ Critical Warnings & Best Practices

When operating gemini-cli-headless in production, you must understand the following critical constraints:

1. Version Lock & System Brittleness

This orchestrator relies on deeply undocumented internal mechanics of the Gemini CLI's policy engine. It is strictly version-locked and certified ONLY for Gemini CLI v0.38.2. Using newer versions may cause the sandbox to silently fail.

• Action: Never auto-update the underlying CLI in your production environments. See Version Lock & Stability for details on breaking changes.

2. Persona Leaking & Workspace Isolation

If you are using system_instruction_override to create a pure data bot, the wrapper defaults to isolate_from_hierarchical_pollution=True. This prevents the CLI from walking up the directory tree and discovering GEMINI.md files from your parent projects.

• Action: Do not disable this flag unless you explicitly want your headless agent to adopt the "Software Engineer" identity of the surrounding workspace.

3. Testing the Sandbox (The Integrity Battery)

Do not use pytest directly to verify the security of the engine. Standard tests only check the model's text output, which is unreliable.

• Action: To verify physical security and cognitive obedience, use our custom Integrity Battery. It executes 29 extreme edge cases and provides a crucial breakdown between [MODEL FAIL] (a cognitive refusal; does not block CI) and [ENGINE FAIL] (a physical sandbox leak; fatally blocks CI).

To prevent leaking API keys to the cloud, testing is handled via a Local Opt-Out Git Hook. The 3-minute Integrity Battery will automatically trigger before code is pushed to your remote repository if any core code files were modified. To bypass the tests (e.g., for simple updates or docs), use the standard Git bypass flag:

git push --no-verify

For more details, see Trace Auditing & Testing.

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Operating System Support

This wrapper is fully tested and supported on both Windows and Linux, automatically adapting its security boundaries to the host OS. For technical details on how OS differences are handled, see Cross-Platform Architecture.