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Dev Mode is for operators who need full control over Custom Rules (custom clauses), the system prompt, and evaluation strategy without the normal guardrails. Turn Dev Mode (advanced) on with the switch in the Custom Rules header. That single flag unlocks advanced clause editing and, farther down the Profile section, the evaluation strategy selector and system prompt controls that are hidden in standard mode.

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Custom clauses: Dynamic Fields vs Raw JSON

With Dev Mode on, Custom Rules no longer use the compact default form. Instead you choose an Editing mode:
ModeWhat you do
Dynamic FieldsEvery clause is its own large text field. You can edit any value, remove a field (including standard ones you do not need), and use Add custom field to create new clause keys beyond identity, personality, purpose, etc.
Raw JSONEdit the entire custom_clauses map as JSON in the code editor (valid object of string values). Use this for bulk copy/paste, merges, or scripted content.
In both modes the clauses object is fully yours: nothing is read-only, and fields you do not want can be deleted (Dynamic: per-field delete; Raw: remove keys from the JSON).
Standard mode only supports the usual fixed clause keys. Dev Mode is what makes arbitrary keys and removals possible.

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Manual system prompt

With Dev Mode enabled, the System Prompt block appears. Turn on Manage system prompt manually to write the prompt yourself in the textarea instead of using auto-generated text from the clauses. You can still insert {{identity}}, {{personality}}, etc. from the tag helper so the manual prompt pulls live values from whatever keys exist in Custom Rules (including custom keys you added in Dynamic Fields or Raw JSON).

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System prompt variables

VariableTypical source clause
{{identity}}identity
{{personality}}personality
{{purpose}}purpose
{{knowledge}}knowledge
{{rules}}rules
{{response_format}}response_format
If you add custom clause keys, reference them in the manual prompt with the same {{key}} pattern. Example: 
<system>
You are {{identity}}.
Tone: {{personality}}

Your primary objective: {{purpose}}

Domain knowledge:
{{knowledge}}

Operating rules:
{{rules}}

Output format:
{{response_format}}
</system>
This pattern works well for Claude-style models with clear XML sections. You keep clause content in Dynamic Fields or Raw JSON, and structure the prompt manually above.

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Evaluation strategy override

With Dev Mode on, Studio stops auto-forcing react when you add MCP servers or Agent-to-Agent links. You set evaluation strategy explicitly and it stays where you put it until you change it.

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Leaving Dev Mode

Disabling Dev Mode returns Custom Rules to the standard form. If you added extra clause keys (not in the default set), Studio warns you that those fields will be dropped when you confirm; only the default clause keys are kept, with your values merged in. If you need that data, copy Raw JSON before switching off.
Turning Dev Mode off also replaces a fully manual system prompt with the auto-generated prompt from your clauses unless you have handled that separately — copy anything you must keep before toggling.

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When to use Dev Mode

  • You need custom clause keys or want to remove standard clauses you do not use.
  • You want full JSON control over clauses for migrations or diffs.
  • You need a fixed evaluation strategy that must not be overridden by tool/A2A autoswitching.
  • You are authoring the system prompt by hand and still want clause variables injected.

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Next steps

Back to Agent Overview

Review the full wizard overview and what’s available in each step.