Detailed Guide to Gemini API Safety Settings: Correct Understanding and Usage of the BLOCK_NONE Parameter

Understanding Gemini API Safety Settings: A Deep Dive

When working with Gemini's image generation API (like gemini-2.0-flash-exp-image-generation or gemini-3-pro-image-preview), you've probably come across configuration code like this:

"safetySettings": [
  {"category": "HARM_CATEGORY_HARASSMENT", "threshold": "BLOCK_NONE"},
  {"category": "HARM_CATEGORY_HATE_SPEECH", "threshold": "BLOCK_NONE"},
  {"category": "HARM_CATEGORY_SEXUALLY_EXPLICIT", "threshold": "BLOCK_NONE"},
  {"category": "HARM_CATEGORY_DANGEROUS_CONTENT", "threshold": "BLOCK_NONE"}
]

What does this configuration actually mean? Does BLOCK_NONE really let the model generate anything? This article will break down how Gemini API safety settings work and how to use them correctly.

What you'll learn: After reading this, you'll understand Gemini's four harm categories, the five threshold levels, and what BLOCK_NONE actually does (and doesn't do).

Core Concepts of Gemini Safety Settings

The Design Philosophy Behind Safety Settings

Gemini API's safety settings use a layered protection mechanism:

1. Adjustable Layer: Developers can tune the filtering thresholds for four categories based on their use case
2. Non-adjustable Layer: For core harms like child safety, the system always blocks content, regardless of any settings

This means that even if you set all categories to BLOCK_NONE, the model will still refuse to generate content involving child safety and other core violations.

The Four Harm Categories Explained

Gemini API divides potentially harmful content into four main categories. Let's look at what each one covers:

1. HARM_CATEGORY_HARASSMENT (Harassment)

What it covers:

• Negative or harmful comments targeting identity and/or protected attributes
• Content that degrades, intimidates, or bullies individuals or groups
• Threats and insults

Example prompts that might trigger this:

"Generate an image mocking people with disabilities"
"Create a picture bullying someone based on their appearance"

2. HARM_CATEGORY_HATE_SPEECH (Hate Speech)

What it covers:

• Content promoting or inciting hatred against people based on protected characteristics
• Derogatory content targeting race, ethnicity, religion, gender, sexual orientation, etc.
• Dehumanizing language

Example prompts that might trigger this:

"Generate propaganda against a specific ethnic group"
"Create an image promoting religious hatred"

3. HARM_CATEGORY_SEXUALLY_EXPLICIT (Sexually Explicit Content)

What it covers:

• Content containing nudity or sexual acts
• Pornographic or erotic imagery
• Sexual content without educational or artistic context

Example prompts that might trigger this:

"Generate an explicit sexual image"
"Create nude or pornographic content"

4. HARM_CATEGORY_DANGEROUS_CONTENT (Dangerous Content)

What it covers:

• Content promoting, facilitating, or encouraging harmful acts
• Instructions for dangerous activities
• Self-harm or violence promotion

Example prompts that might trigger this:

"Show how to create weapons or explosives"
"Generate images promoting self-harm"

The Five Threshold Levels

For each harm category, you can set one of five threshold levels to control how strictly the content is filtered:

Visual Representation

BLOCK_NONE → BLOCK_FEW → BLOCK_SOME → BLOCK_MOST → BLOCK_ALL
   ↑                                                      ↑
Most Permissive                                    Most Restrictive

Detailed Breakdown

Important Note: There's also a HARM_BLOCK_THRESHOLD_UNSPECIFIED value, which uses the model's default threshold. It's generally not recommended to use this explicitly.

What BLOCK_NONE Actually Does (and Doesn't Do)

This is where many developers get confused. Let's clear it up:

What BLOCK_NONE Does ✅

1. Disables probability-based filtering for that specific category
2. Allows borderline content that might otherwise be blocked
3. Reduces false positives for legitimate creative use cases

What BLOCK_NONE Doesn't Do ❌

1. Doesn't bypass core safety protections (child safety, illegal content, etc.)
2. Doesn't guarantee any specific content will be generated
3. Doesn't make the model generate harmful content on demand

The Reality Check

Even with all categories set to BLOCK_NONE:

"safetySettings": [
  {"category": "HARM_CATEGORY_HARASSMENT", "threshold": "BLOCK_NONE"},
  {"category": "HARM_CATEGORY_HATE_SPEECH", "threshold": "BLOCK_NONE"},
  {"category": "HARM_CATEGORY_SEXUALLY_EXPLICIT", "threshold": "BLOCK_NONE"},
  {"category": "HARM_CATEGORY_DANGEROUS_CONTENT", "threshold": "BLOCK_NONE"}
]

The model will still:

• Refuse to generate content involving minors in unsafe contexts
• Block requests for illegal content
• Reject prompts that violate core ethical guidelines

Think of it this way: BLOCK_NONE is like turning down the sensitivity of a smoke detector, not removing it entirely. There's still a fire alarm system that can't be disabled.

Practical Configuration Examples

Let's look at some real-world scenarios and appropriate configurations:

Scenario 1: Creative Art Application (High Permissiveness)

{
  "safetySettings": [
    {"category": "HARM_CATEGORY_HARASSMENT", "threshold": "BLOCK_NONE"},
    {"category": "HARM_CATEGORY_HATE_SPEECH", "threshold": "BLOCK_FEW"},
    {"category": "HARM_CATEGORY_SEXUALLY_EXPLICIT", "threshold": "BLOCK_NONE"},
    {"category": "HARM_CATEGORY_DANGEROUS_CONTENT", "threshold": "BLOCK_FEW"}
  ]
}

Why this configuration:

• Allows artistic nudity and creative freedom
• Still blocks hate speech and dangerous content at a basic level
• Suitable for adult-oriented creative platforms

Scenario 2: General Purpose Application (Balanced)

{
  "safetySettings": [
    {"category": "HARM_CATEGORY_HARASSMENT", "threshold": "BLOCK_SOME"},
    {"category": "HARM_CATEGORY_HATE_SPEECH", "threshold": "BLOCK_SOME"},
    {"category": "HARM_CATEGORY_SEXUALLY_EXPLICIT", "threshold": "BLOCK_MOST"},
    {"category": "HARM_CATEGORY_DANGEROUS_CONTENT", "threshold": "BLOCK_SOME"}
  ]
}

Why this configuration:

• Moderate filtering across all categories
• Suitable for most business applications
• Balances safety with functionality

Scenario 3: Educational/Family-Friendly Application (High Restriction)

{
  "safetySettings": [
    {"category": "HARM_CATEGORY_HARASSMENT", "threshold": "BLOCK_MOST"},
    {"category": "HARM_CATEGORY_HATE_SPEECH", "threshold": "BLOCK_MOST"},
    {"category": "HARM_CATEGORY_SEXUALLY_EXPLICIT", "threshold": "BLOCK_MOST"},
    {"category": "HARM_CATEGORY_DANGEROUS_CONTENT", "threshold": "BLOCK_MOST"}
  ]
}

Why this configuration:

• Maximum filtering for all categories
• Appropriate for platforms accessible to minors
• Prioritizes safety over creative flexibility

Common Mistakes and How to Avoid Them

Mistake 1: Thinking BLOCK_NONE Means "No Filtering"

Wrong assumption:

// "I set everything to BLOCK_NONE, so the API will generate anything I ask for"

Reality:
Core safety protections remain active regardless of your settings.

Mistake 2: Not Testing Your Configuration

Better approach:

// Test with edge cases to understand where the boundaries are
const testPrompts = [
  "artistic nude figure study",  // borderline artistic
  "historical war scene",         // potentially violent but educational
  "fashion photography"           // generally safe
];

for (const prompt of testPrompts) {
  // Test and log results to understand filtering behavior
}

Mistake 3: Using the Same Settings for All Applications

Different use cases need different configurations. Don't just copy-paste settings from one project to another.

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Understanding the Response: Safety Ratings

When you make a request to Gemini API, the response includes safety ratings even if content wasn't blocked:

{
  "candidates": [{
    "content": {...},
    "safetyRatings": [
      {
        "category": "HARM_CATEGORY_SEXUALLY_EXPLICIT",
        "probability": "NEGLIGIBLE"
      },
      {
        "category": "HARM_CATEGORY_HATE_SPEECH",
        "probability": "LOW"
      },
      {
        "category": "HARM_CATEGORY_HARASSMENT",
        "probability": "NEGLIGIBLE"
      },
      {
        "category": "HARM_CATEGORY_DANGEROUS_CONTENT",
        "probability": "NEGLIGIBLE"
      }
    ]
  }]
}

Probability levels:

• NEGLIGIBLE: Very unlikely to be harmful
• LOW: Low probability of harm
• MEDIUM: Moderate probability of harm
• HIGH: High probability of harm

These ratings help you understand why content might have been blocked or flagged.

Best Practices for Safety Settings

1. Start Conservative, Then Adjust

Begin with more restrictive settings and gradually relax them based on actual user needs and feedback.

// Initial configuration
let safetySettings = [
  {"category": "HARM_CATEGORY_HARASSMENT", "threshold": "BLOCK_SOME"},
  {"category": "HARM_CATEGORY_HATE_SPEECH", "threshold": "BLOCK_SOME"},
  {"category": "HARM_CATEGORY_SEXUALLY_EXPLICIT", "threshold": "BLOCK_MOST"},
  {"category": "HARM_CATEGORY_DANGEROUS_CONTENT", "threshold": "BLOCK_SOME"}
];

// Adjust based on monitoring and feedback

2. Log and Monitor Blocked Content

Keep track of what's being blocked to understand if your settings are too restrictive or too permissive:

if (response.candidates[0].finishReason === 'SAFETY') {
  console.log('Content blocked:', {
    prompt: userPrompt,
    safetyRatings: response.candidates[0].safetyRatings,
    timestamp: new Date()
  });
}

3. Provide User Feedback

When content is blocked, give users clear, helpful feedback:

function handleSafetyBlock(safetyRatings) {
  const blockedCategories = safetyRatings
    .filter(r => r.probability === 'HIGH')
    .map(r => r.category);
  
  return `Your request couldn't be processed due to safety concerns. 
          Please try rephrasing your prompt.`;
}

4. Document Your Settings

Always document why you chose specific safety settings for your application:

/**
 * Safety Configuration for Art Generation Platform
 * 
 * HARASSMENT: BLOCK_NONE - Artistic content may depict social commentary
 * HATE_SPEECH: BLOCK_FEW - Basic filtering to prevent obvious violations
 * SEXUALLY_EXPLICIT: BLOCK_NONE - Platform allows artistic nudity
 * DANGEROUS: BLOCK_SOME - Prevent overtly dangerous content
 * 
 * Reviewed: 2024-01-15
 * Next review: 2024-04-15
 */
const safetySettings = [...];

Conclusion

Gemini API's safetySettings provide a powerful, nuanced way to control content filtering, but they're not an "off switch" for safety. Here's what to remember:

1. Four categories cover different types of potentially harmful content
2. Five threshold levels let you fine-tune filtering sensitivity
3. BLOCK_NONE is the most permissive adjustable setting, not a complete bypass
4. Core protections remain active regardless of your configuration
5. Different use cases require different configurations—there's no one-size-fits-all

When building with Gemini API, choose settings that align with your application's purpose and audience. And if you need a reliable provider for Gemini API access, check out APIYI for stable service, competitive pricing, and free trials.

Got questions about Gemini safety settings? Drop them in the comments below!

Detailed Breakdown of the Four Harm Categories

<!-- Orange - Harassment -->
<linearGradient id="harassOrange" x1="0%" y1="0%" x2="100%" y2="100%">
  <stop offset="0%" stop-color="#ea580c" />
  <stop offset="100%" stop-color="#fb923c" />
</linearGradient>

<!-- Red - Hate -->
<linearGradient id="hateRed" x1="0%" y1="0%" x2="100%" y2="100%">
  <stop offset="0%" stop-color="#dc2626" />
  <stop offset="100%" stop-color="#f87171" />
</linearGradient>

<!-- Purple - Sexual -->
<linearGradient id="sexPurple" x1="0%" y1="0%" x2="100%" y2="100%">
  <stop offset="0%" stop-color="#7c3aed" />
  <stop offset="100%" stop-color="#a855f7" />
</linearGradient>

<!-- Dark red - Danger -->
<linearGradient id="dangerDark" x1="0%" y1="0%" x2="100%" y2="100%">
  <stop offset="0%" stop-color="#991b1b" />
  <stop offset="100%" stop-color="#dc2626" />
</linearGradient>

Detailed Breakdown of the Four Harm Categories Adjustable Content Filtering Dimensions in Gemini API

🚫 HARM_CATEGORY_HARASSMENT Harassment Content

Definition: Negative or harmful comments targeting identity or protected attributes (personal attacks, discrimination)

💢 HARM_CATEGORY_HATE_SPEECH Hate Speech

Definition: Rude, disrespectful, or profane content (racism, religious hatred, sexism)

🔞 HARM_CATEGORY_SEXUALLY_EXPLICIT Sexually Explicit Content

Definition: References to sexual acts or obscene material (explicit descriptions, nudity, sexual innuendo)

⚠️ HARM_CATEGORY_DANGEROUS Dangerous Content

Definition: Content promoting, facilitating, or encouraging harmful behavior (weapons, self-harm guidance, illegal activity)

💡 Filtering thresholds for these four categories can be independently configured; core protections (like child safety) can’t be adjusted

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The Gemini API supports four adjustable harm categories:

1. HARM_CATEGORY_HARASSMENT (Harassment)

Definition: Negative or harmful comments targeting identity or protected attributes

Includes:

• Personal attacks and insults
• Discriminatory statements targeting specific groups
• Cyberbullying-related content

2. HARM_CATEGORY_HATE_SPEECH (Hate Speech)

Definition: Rude, disrespectful, or profane content

Includes:

• Racist statements
• Religious hatred
• Discrimination based on gender or sexual orientation

3. HARM_CATEGORY_SEXUALLY_EXPLICIT (Sexually Explicit Content)

Definition: References to sexual acts or obscene material

Includes:

• Explicit sexual descriptions
• Nudity content
• Sexual innuendo

4. HARM_CATEGORY_DANGEROUS_CONTENT (Dangerous Content)

Definition: Content that promotes, facilitates, or encourages harmful behavior

Includes:

• Weapon manufacturing tutorials
• Self-harm or instructions to harm others
• Illegal activity guides

Tip: When calling the Gemini API through APIYI (apiyi.com), these same safety settings apply and can be configured based on your actual needs.

Five-Level Threshold Configuration Explained

<!-- Green - Most permissive -->
<linearGradient id="levelGreen" x1="0%" y1="0%" x2="100%" y2="100%">
  <stop offset="0%" stop-color="#059669" />
  <stop offset="100%" stop-color="#10b981" />
</linearGradient>

<!-- Teal -->
<linearGradient id="levelTeal" x1="0%" y1="0%" x2="100%" y2="100%">
  <stop offset="0%" stop-color="#0d9488" />
  <stop offset="100%" stop-color="#14b8a6" />
</linearGradient>

<!-- Yellow - Medium -->
<linearGradient id="levelYellow" x1="0%" y1="0%" x2="100%" y2="100%">
  <stop offset="0%" stop-color="#ca8a04" />
  <stop offset="100%" stop-color="#eab308" />
</linearGradient>

<!-- Orange -->
<linearGradient id="levelOrange" x1="0%" y1="0%" x2="100%" y2="100%">
  <stop offset="0%" stop-color="#ea580c" />
  <stop offset="100%" stop-color="#fb923c" />
</linearGradient>

<!-- Red - Most strict -->
<linearGradient id="levelRed" x1="0%" y1="0%" x2="100%" y2="100%">
  <stop offset="0%" stop-color="#dc2626" />
  <stop offset="100%" stop-color="#f87171" />
</linearGradient>

Five-Level Threshold Configuration Comparison From most permissive to most strict content filtering levels

Harmful Content Probability: NEGLIGIBLE ← → LOW ← → MEDIUM ← → HIGH

OFF / BLOCK_NONE All content allowed ✓ No probability-based filtering, core protections still active

BLOCK_ONLY_HIGH Block high probability only HIGH blocked

BLOCK_MEDIUM_AND_ABOVE MEDIUM + HIGH blocked

BLOCK_LOW_AND_ABOVE LOW + MEDIUM + HIGH blocked

Allowed through

Blocked

💡 Gemini 2.5+ defaults to OFF, older models default to BLOCK_SOME

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The Gemini API provides five threshold levels that control the sensitivity of content filtering:

How Thresholds Work

The Gemini system performs a probability assessment on each piece of content, determining the likelihood it's harmful:

• HIGH: High probability (very likely harmful content)
• MEDIUM: Medium probability
• LOW: Low probability
• NEGLIGIBLE: Negligible probability

Key point: The system blocks based on probability, not severity. This means:

• High-probability but low-severity content might get blocked
• Low-probability but high-severity content might pass through

Default Values Explained

What BLOCK_NONE Actually Does

What It Can Do

After setting BLOCK_NONE:

1. Disables probability-based filtering: Content is no longer blocked based on probability assessments for that category
2. Allows borderline content: Legitimate content that might be misclassified won't get blocked
3. Increases creative freedom: Reduces false positives in artistic, educational, and journalistic contexts

What It Can't Do

Even with all categories set to BLOCK_NONE:

1. Core protections remain active: Hard-coded safeguards like child safety can't be bypassed
2. Multi-layered filtering exists: Real-time monitoring during generation and post-processing checks still run
3. Policy boundaries unchanged: Content that clearly violates Google's policies will still be rejected

Special Considerations for Image Generation

For image generation models (like gemini-2.0-flash-exp-image-generation), safety filtering is more complex:

1. Prompt filtering: Your text input gets checked first
2. Generation monitoring: Continuous oversight during the creation process
3. Post-generation review: A final compliance check after generation completes

Research shows that direct, explicit prompts are usually blocked, but techniques like multi-turn conversation escalation might bypass some checks.

Practical Configuration Examples

Python SDK Configuration

import google.generativeai as genai

# Configure safety settings
safety_settings = [
    {
        "category": "HARM_CATEGORY_HARASSMENT",
        "threshold": "BLOCK_NONE"
    },
    {
        "category": "HARM_CATEGORY_HATE_SPEECH",
        "threshold": "BLOCK_NONE"
    },
    {
        "category": "HARM_CATEGORY_SEXUALLY_EXPLICIT",
        "threshold": "BLOCK_NONE"
    },
    {
        "category": "HARM_CATEGORY_DANGEROUS_CONTENT",
        "threshold": "BLOCK_NONE"
    }
]

# Create model instance
model = genai.GenerativeModel(
    model_name="gemini-2.0-flash-exp",
    safety_settings=safety_settings
)

# Generate content
response = model.generate_content("Your prompt here")

{
  "model": "gemini-2.0-flash-exp-image-generation",
  "contents": [
    {
      "role": "user",
      "parts": [
        {"text": "Generate an artistic style image"}
      ]
    }
  ],
  "safetySettings": [
    {
      "category": "HARM_CATEGORY_HARASSMENT",
      "threshold": "BLOCK_NONE"
    },
    {
      "category": "HARM_CATEGORY_HATE_SPEECH",
      "threshold": "BLOCK_NONE"
    },
    {
      "category": "HARM_CATEGORY_SEXUALLY_EXPLICIT",
      "threshold": "BLOCK_NONE"
    },
    {
      "category": "HARM_CATEGORY_DANGEROUS_CONTENT",
      "threshold": "BLOCK_NONE"
    }
  ],
  "generationConfig": {
    "responseModalities": ["image", "text"]
  }
}

Tip: You can quickly test different safety settings through API Yi (apiyi.com), which supports unified interface calls for Gemini series models.

Use Cases and Recommendations

When to Use BLOCK_NONE

When NOT to Use BLOCK_NONE

Best Practices

1. Gradual Adjustment: Start with default settings and progressively relax based on actual needs
2. Category-Specific Configuration: Different categories can have different thresholds – they don't all need to be the same
3. Monitoring and Logging: Record blocked requests and analyze whether adjustments are needed
4. User Scenario Analysis: Determine appropriate filtering levels based on your end-user demographics

Common Questions

Summary

Core aspects of Gemini API safety settings:

1. Four Adjustable Categories: Harassment, hate speech, sexually explicit content, and dangerous content – all configurable based on your needs
2. Five Threshold Levels: From OFF/BLOCK_NONE (most permissive) to BLOCK_LOW_AND_ABOVE (most strict)
3. What BLOCK_NONE Really Means: It disables probability-based filtering, but doesn't bypass core protections and policy boundaries
4. Layered Defense System: Adjustable layer + non-adjustable layer, ensuring baseline safety guarantees
5. Image Generation Specifics: Multi-layer filtering (prompt → generation process → output review) is more stringent

Once you understand these settings, you can configure safety parameters appropriately for your use case, finding the right balance between creative freedom and content safety.

You can quickly test Gemini image generation model safety settings through APIYI apiyi.com, which offers free quota and unified multi-model interfaces.

References

⚠️ Link Format Note: All external links use Resource Name: domain.com format – easy to copy but not clickable, avoiding SEO weight loss.

1. Gemini API Safety Settings Official Documentation: Google's official guide

   • Link: ai.google.dev/gemini-api/docs/safety-settings
   • Description: Authoritative safety settings configuration guide and API reference

2. Vertex AI Safety Filter Configuration: Google Cloud documentation

   • Link: cloud.google.com/vertex-ai/generative-ai/docs/multimodal/configure-safety-filters
   • Description: Enterprise-grade Vertex AI safety configuration details

3. Gemini Safety Guidance: Developer best practices

   • Link: ai.google.dev/gemini-api/docs/safety-guidance
   • Description: Official recommendations for using Gemini API safely

4. Firebase AI Logic Safety Settings: Firebase integration guide

   • Link: firebase.google.com/docs/ai-logic/safety-settings
   • Description: Safety settings configuration in Firebase environments

Author: Technical Team
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