Headless Mode

Headless mode allows you to run Gemini CLI programmatically from command line scripts and automation tools without any interactive UI. This is ideal for scripting, automation, CI/CD pipelines, and building AI-powered tools.

• Headless Mode
  • Overview
  • Basic Usage
    • Direct Prompts
    • Stdin Input
    • Combining with File Input
  • Output Formats
    • Text Output (Default)
    • JSON Output
      • Response Schema
      • Example Usage
    • File Redirection
  • Configuration Options
  • Examples
    • Code review
    • Generate commit messages
    • API documentation
    • Batch code analysis
    • Code review
    • Log analysis
    • Release notes generation
    • Model and tool usage tracking
  • Resources

Overview

The headless mode provides a headless interface to Gemini CLI that:

• Accepts prompts via command line arguments or stdin
• Returns structured output (text or JSON)
• Supports file redirection and piping
• Enables automation and scripting workflows
• Provides consistent exit codes for error handling

Basic Usage

Direct Prompts

Use the --prompt (or -p) flag to run in headless mode:

gemini --prompt "What is machine learning?"

Stdin Input

Pipe input to Gemini CLI from your terminal:

echo "Explain this code" | gemini

Combining with File Input

Read from files and process with Gemini:

cat README.md | gemini --prompt "Summarize this documentation"

Output Formats

Text Output (Default)

Standard human-readable output:

gemini -p "What is the capital of France?"

Response format:

The capital of France is Paris.

JSON Output

Returns structured data including response, statistics, and metadata. This format is ideal for programmatic processing and automation scripts.

Response Schema

The JSON output follows this high-level structure:

{
  "response": "string", // The main AI-generated content answering your prompt
  "stats": {
    // Usage metrics and performance data
    "models": {
      // Per-model API and token usage statistics
      "[model-name]": {
        "api": {
          /* request counts, errors, latency */
        },
        "tokens": {
          /* prompt, response, cached, total counts */
        }
      }
    },
    "tools": {
      // Tool execution statistics
      "totalCalls": "number",
      "totalSuccess": "number",
      "totalFail": "number",
      "totalDurationMs": "number",
      "totalDecisions": {
        /* accept, reject, modify, auto_accept counts */
      },
      "byName": {
        /* per-tool detailed stats */
      }
    },
    "files": {
      // File modification statistics
      "totalLinesAdded": "number",
      "totalLinesRemoved": "number"
    }
  },
  "error": {
    // Present only when an error occurred
    "type": "string", // Error type (e.g., "ApiError", "AuthError")
    "message": "string", // Human-readable error description
    "code": "number" // Optional error code
  }
}

Example Usage

gemini -p "What is the capital of France?" --output-format json

Response:

{
  "response": "The capital of France is Paris.",
  "stats": {
    "models": {
      "gemini-2.5-pro": {
        "api": {
          "totalRequests": 2,
          "totalErrors": 0,
          "totalLatencyMs": 5053
        },
        "tokens": {
          "prompt": 24939,
          "candidates": 20,
          "total": 25113,
          "cached": 21263,
          "thoughts": 154,
          "tool": 0
        }
      },
      "gemini-2.5-flash": {
        "api": {
          "totalRequests": 1,
          "totalErrors": 0,
          "totalLatencyMs": 1879
        },
        "tokens": {
          "prompt": 8965,
          "candidates": 10,
          "total": 9033,
          "cached": 0,
          "thoughts": 30,
          "tool": 28
        }
      }
    },
    "tools": {
      "totalCalls": 1,
      "totalSuccess": 1,
      "totalFail": 0,
      "totalDurationMs": 1881,
      "totalDecisions": {
        "accept": 0,
        "reject": 0,
        "modify": 0,
        "auto_accept": 1
      },
      "byName": {
        "google_web_search": {
          "count": 1,
          "success": 1,
          "fail": 0,
          "durationMs": 1881,
          "decisions": {
            "accept": 0,
            "reject": 0,
            "modify": 0,
            "auto_accept": 1
          }
        }
      }
    },
    "files": {
      "totalLinesAdded": 0,
      "totalLinesRemoved": 0
    }
  }
}

File Redirection

Save output to files or pipe to other commands:

# Save to file
gemini -p "Explain Docker" > docker-explanation.txt
gemini -p "Explain Docker" --output-format json > docker-explanation.json

# Append to file
gemini -p "Add more details" >> docker-explanation.txt

# Pipe to other tools
gemini -p "What is Kubernetes?" --output-format json | jq '.response'
gemini -p "Explain microservices" | wc -w
gemini -p "List programming languages" | grep -i "python"

Configuration Options

Key command-line options for headless usage:

Option	Description	Example
--prompt, -p	Run in headless mode	gemini -p "query"
--output-format	Specify output format (text, json)	gemini -p "query" --output-format json
--model, -m	Specify the Gemini model	gemini -p "query" -m gemini-2.5-flash
--debug, -d	Enable debug mode	gemini -p "query" --debug
--all-files, -a	Include all files in context	gemini -p "query" --all-files
--include-directories	Include additional directories	gemini -p "query" --include-directories src,docs
--yolo, -y	Auto-approve all actions	gemini -p "query" --yolo
--approval-mode	Set approval mode	gemini -p "query" --approval-mode auto_edit

For complete details on all available configuration options, settings files, and environment variables, see the Configuration Guide.

Examples

Code review

cat src/auth.py | gemini -p "Review this authentication code for security issues" > security-review.txt

Generate commit messages

result=$(git diff --cached | gemini -p "Write a concise commit message for these changes" --output-format json)
echo "$result" | jq -r '.response'

API documentation

result=$(cat api/routes.js | gemini -p "Generate OpenAPI spec for these routes" --output-format json)
echo "$result" | jq -r '.response' > openapi.json

Batch code analysis

for file in src/*.py; do
    echo "Analyzing $file..."
    result=$(cat "$file" | gemini -p "Find potential bugs and suggest improvements" --output-format json)
    echo "$result" | jq -r '.response' > "reports/$(basename "$file").analysis"
    echo "Completed analysis for $(basename "$file")" >> reports/progress.log
done

Code review

result=$(git diff origin/main...HEAD | gemini -p "Review these changes for bugs, security issues, and code quality" --output-format json)
echo "$result" | jq -r '.response' > pr-review.json

Log analysis

grep "ERROR" /var/log/app.log | tail -20 | gemini -p "Analyze these errors and suggest root cause and fixes" > error-analysis.txt

Release notes generation

result=$(git log --oneline v1.0.0..HEAD | gemini -p "Generate release notes from these commits" --output-format json)
response=$(echo "$result" | jq -r '.response')
echo "$response"
echo "$response" >> CHANGELOG.md

Model and tool usage tracking

result=$(gemini -p "Explain this database schema" --include-directories db --output-format json)
total_tokens=$(echo "$result" | jq -r '.stats.models // {} | to_entries | map(.value.tokens.total) | add // 0')
models_used=$(echo "$result" | jq -r '.stats.models // {} | keys | join(", ") | if . == "" then "none" else . end')
tool_calls=$(echo "$result" | jq -r '.stats.tools.totalCalls // 0')
tools_used=$(echo "$result" | jq -r '.stats.tools.byName // {} | keys | join(", ") | if . == "" then "none" else . end')
echo "$(date): $total_tokens tokens, $tool_calls tool calls ($tools_used) used with models: $models_used" >> usage.log
echo "$result" | jq -r '.response' > schema-docs.md
echo "Recent usage trends:"
tail -5 usage.log

Resources

• CLI Configuration - Complete configuration guide
• Authentication - Setup authentication
• Commands - Interactive commands reference
• Tutorials - Step-by-step automation guides