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Spec-first AI prompt for autonomous software development

FreeFree tier
Type
Open Source
Visit Website GitHub (40 stars)

About prompt

An open-source system prompt designed to guide an AI assistant or AI coding agent to act as a Spec-Driven Development Architect. The prompt enforces a spec-first, code-second methodology, requiring the agent to produce detailed specification packages before any implementation. It defines core principles including delta specs for changes, small phases (1–3 hours of agentic coding), RFC 2119 keyword discipline, and explicit rejection of scope creep. The output structure includes files such as mission.md, tech-stack.md, roadmap.md, validation.md for new projects, and proposal.md, requirements.md, scenarios.md, out-of-scope.md for features or changes. The prompt is intended to reduce ambiguity and ensure verifiable increments, serving as a contract between product intent and implementation.

Key Features

Spec-first methodology – code is never emitted unless explicitly requested
Delta specs for changes (ADDED/MODIFIED/REMOVED against baseline)
Small phases time-boxed to 1–3 hours of agentic coding
RFC 2119 keyword discipline in requirements (MUST, SHALL, SHOULD, MAY, MUST NOT)
Explicit rejection of scope creep with out-of-scope lists
Structured output: mission.md, tech-stack.md, roadmap.md, validation.md for new projects
GIVEN/WHEN/THEN acceptance scenarios covering happy path and edge cases
Grouped requirements by domain with links to scenarios
Non-functional requirements (performance, security, accessibility) required
Support for existing system modifications via feature/change spec packages

Pros & Cons

Pros
  • Enforces rigorous specification before coding, reducing ambiguity and rework
  • Decomposes work into small, verifiable increments that are easy to manage
  • Uses industry-standard RFC 2119 language for clear, testable requirements
  • Explicitly manages scope creep by listing out-of-scope items
  • Provides reusable, well-structured templates for specs across projects
  • Designed for AI agents, but also useful for human developers
Cons
  • Requires familiarity with RFC 2119 and the spec package format
  • May be overly verbose for trivial or one-line changes
  • Primarily designed for AI agents; may not fit all human team workflows without adaptation
  • Focuses only on the specification phase; does not generate code directly
  • Assumes the agent can follow structured output precisely, which may require prompt orchestration

Best For

Autonomous AI coding agents that produce specs before writing codeHuman developers following a rigorous spec-driven approachDesigning new software projects with clear, verifiable specificationsModifying existing systems with delta specs to track changesEnsuring alignment between product intent and implementation in agentic workflowsTeaching or standardizing specification-driven development practices

FAQ

What is a Spec-Driven Development Architect?
A role that designs software exclusively through precise, verifiable specifications before any code is written. This prompt instructs an AI to act as that architect.
What output does this prompt produce?
For new projects: a spec package with mission.md, tech-stack.md, roadmap.md, and validation.md. For changes: proposal.md, requirements.md, scenarios.md, validation.md, and out-of-scope.md.
What are the core principles of this prompt?
Spec-first, code-second; delta specs for changes; small phases (1–3 hours of agentic coding); explicit rejection of scope creep; and RFC 2119 keyword discipline.
How does it handle changes to existing systems?
It produces delta specs with sections marked ADDED, MODIFIED, or REMOVED against the current baseline, stored under specs/changes/YYYY-MM-DD-feature-name/.