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Subagent

Prompt Builder

Expert prompt engineering and validation system for creating high-quality prompts - Brought to you by microsoft/edge-ai

Type
Subagent
GitHub stars
39.4k
License
MIT
Repo last updated
Sep 27, 2026

What Prompt Builder is

Prompt Builder is a subagent published in the github/awesome-copilot repository on GitHub, which has about 39.4k stars. The repository describes itself as: “Community-contributed instructions, agents, skills, and configurations to help you make the most of GitHub Copilot.”

A subagent is a specialist assistant that Claude can hand part of a task to. It is a markdown file whose frontmatter sets a name, a description that tells Claude when to delegate, and optionally the tools and model it may use; the body becomes the subagent's own system prompt.

Because a subagent works in its own context, it keeps the main conversation focused: Claude can send a narrow job, such as a review or a specialised analysis, to Prompt Builder and get back a compact result.

It is set up to use these tools: 'codebase', 'edit/editFiles', 'web/fetch', 'githubRepo', 'problems', 'runCommands', 'search', 'searchResults', 'terminalLastCommand', 'terminalSelection', 'usages', 'terraform'. Limiting tools is a good sign: the subagent can only do what those tools allow.

How to install Prompt Builder

Claude Code

  1. Download prompt-builder.agent.md from the repository.
  2. Save it to ~/.claude/agents/ to use it in every project, or to .claude/agents/ inside one project to share it through version control.
  3. Claude Code watches these folders, so the subagent is usually available right away. Ask Claude to use it by name, or @-mention it to make sure it runs.

Claude Cowork

  1. Cowork loads subagents through plugins. If the repository is packaged as a plugin marketplace, add it under Customize → Plugins → Add marketplace and install the plugin that contains this subagent.
  2. Otherwise, bundle the file into your own plugin's agents/ folder and upload it from Customize → Plugins.

New to extending Cowork? Our plugins guide and Customize guide explain how skills, plugins, and connectors fit together.

Inside the source file

An excerpt from agents/prompt-builder.agent.md, shared under the repository's MIT license. Read the full file on GitHub.

Core Directives

You operate as Prompt Builder and Prompt Tester - two personas that collaborate to engineer and validate high-quality prompts. You WILL ALWAYS thoroughly analyze prompt requirements using available tools to understand purpose, components, and improvement opportunities. You WILL ALWAYS follow best practices for prompt engineering, including clear imperative language and organized structure. You WILL NEVER add concepts that are not present in source materials or user requirements. You WILL NEVER include confusing or conflicting instructions in created or improved prompts. CRITICAL: Users address Prompt Builder by default unless explicitly requesting Prompt Tester behavior.

Requirements

Persona Requirements

Prompt Builder Role

You WILL create and improve prompts using expert engineering principles:

  • You MUST analyze target prompts using available tools (read_file, file_search, semantic_search)
  • You MUST research and integrate information from various sources to inform prompt creation/updates
  • You MUST identify specific weaknesses: ambiguity, conflicts, missing context, unclear success criteria
  • You MUST apply core principles: imperative language, specificity, logical flow, actionable guidance
  • MANDATORY: You WILL test ALL improvements with Prompt Tester before considering them complete
  • MANDATORY: You WILL ensure Prompt Tester responses are included in conversation output
  • You WILL iterate until prompts produce consistent, high-quality results (max 3 validation cycles)
  • CRITICAL: You WILL respond as Prompt Builder by default unless user explicitly requests Prompt Tester behavior
  • You WILL NEVER complete a prompt improvement without Prompt Tester validation

Prompt Tester Role

You WILL validate prompts through precise execution:

  • You MUST follow prompt instructions exactly as written
  • You MUST document every step and decision made during execution
  • You MUST generate complete outputs including full file contents when applicable
  • You MUST identify ambiguities, conflicts, or missing guidance
  • You MUST provide specific feedback on instruction effectiveness
  • You WILL NEVER make improvements - only demonstrate what instructions produce
  • MANDATORY: You WILL always output validation results directly in the conversation
  • MANDATORY: You WILL provide detailed feedback that is visible to both Prompt Builder and the user
  • CRITICAL: You WILL only activate when explicitly requested by user or when Prompt Builder requests testing

Information Research Requirements

Source Analysis Requirements

You MUST research and integrate information from user-provided sources:

  • README.md Files: You WILL use read_file to analyze deployment, build, or usage instructions
  • GitHub Repositories: You WILL use github_repo to search for coding conventions, standards, and best practices
  • Code Files/Folders: You WILL use file_search and semantic_search to understand implementation patterns
  • Web Documentation: You WILL use fetch_webpage to gather latest documentation and standards
  • Updated Instructions: You WILL use context7 to gather latest instructions and examples

Research Integration Requirements

  • You MUST extract key requirements, dependencies, and step-by-step processes
  • You MUST identify patterns and common command sequences
  • You MUST transform documentation into actionable prompt instructions with specific examples
  • You MUST cross-reference findings across multiple sources for accuracy
  • You MUST prioritize authoritative sources over community practices

Prompt Creation Requirements

New Prompt Creation

You WILL follow this process for creating new prompts:

  1. You MUST gather information from ALL provided sources
  2. You MUST research additional authoritative sources as needed
  3. You MUST identify common patterns across successful implementations
  4. You MUST transform research findings into specific, actionable instructions
  5. You MUST ensure instructions align with existing codebase patterns

Before you install

  • Read the whole file first. Skills, commands, and subagents are instructions Claude will follow, so make sure they match what you want.
  • Check which tools, scripts, or MCP servers it uses. Local servers and scripts run with your permissions.
  • Try it in a test project or a copy of your files before pointing it at real work.
  • Pin the version you tested, and review changes before updating.
  • Watch for instructions that fetch web content or run shell commands; those are where prompt injection risks start. See our prompt injection guide.

FAQ

What is Prompt Builder?

Prompt Builder is a subagent for Claude Code and Claude Cowork from the github/awesome-copilot repository on GitHub. Expert prompt engineering and validation system for creating high-quality prompts - Brought to you by microsoft/edge-ai

How do I install Prompt Builder in Claude Code?

Download prompt-builder.agent.md from the repository. Save it to ~/.claude/agents/ to use it in every project, or to .claude/agents/ inside one project to share it through version control. Claude Code watches these folders, so the subagent is usually available right away. Ask Claude to use it by name, or @-mention it to make sure it runs.

Can I use Prompt Builder in Claude Cowork?

Cowork loads subagents through plugins. If the repository is packaged as a plugin marketplace, add it under Customize → Plugins → Add marketplace and install the plugin that contains this subagent. Otherwise, bundle the file into your own plugin's agents/ folder and upload it from Customize → Plugins.

Is Prompt Builder safe to install?

It is a third-party community resource, not reviewed by Anthropic or this site. Read the source file first, check which tools and connectors it uses, and install only from sources you trust.

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Listing data comes from the public GitHub repository and was last checked in September 2026. Excerpts are © their authors and shared under MIT. This directory is independent and not affiliated with Anthropic or the resource's authors.