[Feature Request] Restore system-prompt-{mode-slug} Override Capability for Custom Modes

[StellaHermes]

Problem (one or two sentences)

Summary

Request to restore the system-prompt-{mode-slug} file override mechanism that was removed in recent versions, or provide an alternative way to completely replace the system prompt for custom modes.

Context (who is affected and when)

Background

In previous versions of Roo Code, users could create system-prompt-{mode-slug} files in the .roo/ directory to completely override the system prompt for custom modes. This functionality has been removed in recent updates, replaced with roleDefinition and customInstructions which only append to the base system prompt rather than replacing it.

Use Case

I have developed a sophisticated multi-mode academic research workflow with 4 custom modes:

• 🕯️ Disputer (Academic Dialogue)
• 🏛️ Weaver (Academic Writing)
• 🌫️ Lector (Literature Review)
• 🏔️ Polisher (Academic Refinement)

Each mode has a carefully crafted system prompt (1,300-2,300 lines) that defines:

• Specific persona and behavioral patterns
• Domain-specific methodologies (legal research methods)
• Complex interaction protocols (e.g., Disputatio dialogue format)
• Strict output formatting rules

The current append-only mechanism causes issues:

1. Prompt pollution: The base system prompt conflicts with my custom instructions
2. Behavioral inconsistency: AI receives mixed signals from base + custom prompts
3. Loss of control: Cannot ensure AI follows only my carefully designed instructions
4. Token waste: Base prompt consumes tokens unnecessarily

Why This Matters

Many advanced users (researchers, specialized domains) need complete control over the system prompt to:

• Implement domain-specific AI behaviors
• Ensure consistency with established workflows
• Maintain precise control over AI output format
• Avoid conflicts between base and custom instructions

Desired behavior (conceptual, not technical)

Proposed Solutions

Option 1: Restore system-prompt-{mode-slug} Override (Preferred)

Bring back the ability to completely replace the system prompt via files in .roo/system-prompt-{mode-slug}

Option 2: Add Configuration Flag

Add a configuration option in .roomodes:

customModes:
  - slug: my-mode
    name: My Mode
    overrideSystemPrompt: true  # New flag
    roleDefinition: [complete custom prompt]

Option 3: Separate "Advanced Mode" Setting

Add a global setting: "roo.advancedMode.allowSystemPromptOverride": true

• Default: false (current behavior)
• When enabled: roleDefinition completely replaces base prompt

Impact

• Backward compatibility: Users who don't need this feature are unaffected
• Power users: Regain full control over AI behavior
• Use cases: Academic research, specialized domains, complex workflows

Current Workaround

I've had to rollback to an older version of Roo Code, which:

• ❌ Misses new features and bug fixes
• ❌ May have compatibility issues with future VS Code updates
• ❌ Requires manual version management

Community Support

I believe many advanced users would benefit from this feature. I'm happy to:

• Provide detailed documentation of my use case
• Test beta implementations
• Contribute to documentation

Related

This is similar to how Cursor handles .cursorrules - while it appends to base prompt, the priority is high enough that it effectively overrides base behavior in most cases.

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Thank you for considering this request! Roo Code is an excellent tool, and restoring this capability would make it perfect for advanced, specialized workflows.

Constraints / preferences (optional)

No response

Request checklist

• I've searched existing Issues and Discussions for duplicates
• This describes a specific problem with clear context and impact

Roo Code Task Links (optional)

No response

Acceptance criteria (optional)

No response

Proposed approach (optional)

No response

Trade-offs / risks (optional)

No response

[roomote]

I have analyzed this issue and explored the relevant codebase. Here is my proposed implementation plan:

Analysis

The system prompt is currently built in src/core/prompts/system.ts via generatePrompt(). It always assembles a fixed structure: roleDefinition at the top, followed by MARKDOWN RULES, TOOL USE, CAPABILITIES, MODES, SKILLS, RULES, SYSTEM INFO, OBJECTIVE, and finally CUSTOM INSTRUCTIONS at the bottom. There is no way for a custom mode to bypass these standard sections -- roleDefinition and customInstructions only control the top and bottom portions.

Tool definitions are sent natively (not embedded in the system prompt), so replacing the system prompt would not break tool calling.

Proposed Approach: overrideSystemPrompt flag on ModeConfig (Issue Option 2)

This aligns best with the existing architecture and avoids introducing file-based override mechanisms.

Changes

1. packages/types/src/mode.ts -- Add overrideSystemPrompt: z.boolean().optional() to modeConfigSchema. Defaults to false/undefined (current behavior).

2. src/core/prompts/system.ts -- In generatePrompt(), when the resolved mode config has overrideSystemPrompt: true, use roleDefinition as the entire system prompt body, only appending custom instructions (global + mode-specific + .roo/rules-* files) at the end. All standard sections (TOOL USE, CAPABILITIES, MODES, SKILLS, RULES, SYSTEM INFO, OBJECTIVE, MARKDOWN RULES) are skipped.

3. src/shared/modes.ts -- Pass through overrideSystemPrompt in getModeSelection() so the flag is available in generatePrompt().

4. Tests -- Add test cases in src/core/prompts/__tests__/system-prompt.spec.ts to verify:

   • When overrideSystemPrompt: true, the prompt uses only roleDefinition + custom instructions
   • When overrideSystemPrompt: false or absent, behavior is unchanged
   • Standard sections are absent when override is active

Usage Example

In .roomodes or VS Code settings:

{
  "customModes": [
    {
      "slug": "disputer",
      "name": "Disputer",
      "roleDefinition": "[Your complete 1300+ line system prompt here]",
      "overrideSystemPrompt": true,
      "groups": ["read", "edit"]
    }
  ]
}

What users still get with the override

• Tool calling works normally (tools are sent natively, not in the system prompt)
• Custom instructions from .roo/rules-* files and global settings are still appended
• Mode switching and tool group restrictions still apply

What is skipped

• All built-in prompt sections (CAPABILITIES, TOOL USE guidelines, MODES listing, SKILLS, RULES formatting, SYSTEM INFO, OBJECTIVE, MARKDOWN RULES)
• Users take full responsibility for prompt content

Backward compatibility

• overrideSystemPrompt defaults to false/undefined, so all existing modes behave exactly as before
• No breaking changes for any user who does not explicitly opt in

Please mention @roomote in a comment saying that you approve this plan, and I will proceed with the implementation.

[StellaHermes]

@roomote I approve this plan. Thank you for the quick response and well-thought-out implementation.

This solution perfectly addresses my use case while maintaining backward compatibility. I'm looking forward to testing it once implemented.

[roomote]

I've seen the approval and will proceed with the implementation now. I'll open a draft PR to share progress shortly.

[roomote]

Opened a draft PR with my attempt at implementing the overrideSystemPrompt option: #11794

The PR adds an optional overrideSystemPrompt: true flag to ModeConfig that causes the system prompt to use only the roleDefinition as its body, skipping all standard sections. Custom instructions from .roo/rules-* files and global settings are still appended. Feedback welcome!