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Builder Builder
2026 Respawn OSS

Prompts

Builder reads prompt context from global and workspace files.

Instruction Files

Section titled “Instruction Files”
  • ~/.builder/AGENTS.md is a global instructions file injected into every session.
  • <workspace>/AGENTS.md adds developer instructions that are specific to the current project.

Builder injects these files into the conversation as developer context once per session, not as the main system prompt.

System Prompt

Section titled “System Prompt”

System prompt files replace Builder’s built-in main system prompt for new sessions.

Priority, lowest to highest:

  • Built-in system prompt
  • ~/.builder/SYSTEM.md
  • ~/.builder/config.toml system_prompt_file
  • <workspace-root>/.builder/SYSTEM.md
  • <workspace-root>/.builder/config.toml system_prompt_file
  • Selected [subagents.<role>] system_prompt_file

system_prompt_file paths are resolved relative to the containing config.toml directory unless absolute.

Builder reads and renders the selected system prompt file once when the session sends its first model request, stores the fully rendered result in the system_prompt session metadata, and reuses that snapshot for later requests. After a session has stored that snapshot, editing prompt files affects new sessions only. Sessions without system_prompt capture the current prompt file on their next model request.

Placeholders

Section titled “Placeholders”

System prompt files use Go template syntax with these fields:

  • {{.BuilderRunCommand}} - command prefix for launching Builder subagents from shell, e.g. path/to/builder.exe
  • {{.EstimatedToolCallsForContext}} - estimated function/tool-call budget before compaction/handoff, exact number that varies with model context window, like 185.
  • {{.EditingToolName}} - name of the tool the agent uses to modify files, like edit or patch. Varies per model.
  • {{.DefaultSystemPrompt}} - Full text of the original Builder system prompt, positioning the agent as an expert architect, product engineer, coding agent.

Example:

{{.DefaultSystemPrompt}}


# Team Rules


Prefer small, reviewable commits.

Tool preambles are appended after the rendered SYSTEM.md when tool_preambles = true for the locked session.

Supervisor System Prompt

Section titled “Supervisor System Prompt”

reviewer.system_prompt_file replaces Builder’s built-in supervisor system prompt:

  • ~/.builder/config.toml
  • <workspace-root>/.builder/config.toml

The workspace config value takes priority. Editing the file affects only sessions that have not run the supervisor with that override.

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