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Chapter 33: Tessl and SpecifyPlus - The Ultimate Workflow

You've mastered SpecifyPlus's opinionated workflow: Constitution → Specify → Plan → Tasks → Implement. The PHRs and ADRs are there. You've learned how specifications serve as the coordination layer for AI agents. Now you're ready for the next evolution: integrating Tessl with SpecifyPlus to create the most powerful specification-driven development workflow available in 2025.

This chapter shows you how to marry two complementary approaches:

SpecifyPlus provides the workflow structure—the human-gated, multi-phase process that ensures you build the right thing with clear organizational guardrails.

Tessl provides the infrastructure—versioned usage specs that prevent API hallucinations, framework-level enforcement of spec-first patterns, and long-term memory through specifications stored in your codebase.

Together, they create something neither achieves alone: a complete system for reliable, professional AI-assisted development that scales from solo projects to enterprise teams.

The Marriage: How SpecifyPlus and Tessl Complement Each Other​

Think of this integration like a professional kitchen:

SpecifyPlus is your recipe and workflow—it tells you what to cook, when to add each ingredient, and how to verify the dish is correct. It provides structure: constitution sets the standards, specification defines the goals, plan maps the implementation, tasks break it into atomic steps.

Tessl is your ingredient quality system—it ensures every ingredient (library, API, framework) is exactly what you think it is. No outdated packages, no hallucinated APIs, no mixed versions. It also provides persistent memory so future chefs (or your future self) remember why certain ingredients were chosen.

The Big Picture​

Tessl represents the evolution of everything you've learned so far:

Spec-Kit Plus teaches you to write specifications first and gives you a structured workflow (Constitution → Specify → Plan → Tasks). It's a methodology you adopt with discipline.

Tessl enforces that methodology at the framework level. It won't let agents rush to code. It provides versioned library documentation so agents can't hallucinate APIs. It stores specifications in your codebase as long-term memory so agents remember decisions across sessions.

Together, they're more powerful than either alone:

  • Use SpecifyPlus for your high-level workflow and project structure
  • Use Tessl Registry to prevent API hallucinations for every library
  • Explore Tessl Framework to enforce spec-first patterns and regenerate code from specs

This chapter shows you how to combine these tools to build software at a level of reliability and scale that was previously impossible for solo developers or small teams.

Chapter Structure​

The lessons build progressively:

Lessons 1-3 establish the problem and Tessl's solution at a conceptual level. You'll understand why Tessl exists and what makes it different from everything else.

Lessons 4-6 are hands-on: installing Tessl, creating your first spec, and integrating it with your existing SpecifyPlus workflows.

Lessons 7-9 go deeper: understanding the three-stage evolution of SDD, publishing custom specs for your organization, and studying real-world production systems.

Lesson 10 concludes with the future vision: a world where you work primarily at the specification level, with code as a generated artifact you rarely need to see.

Why SpecifyPlus Alone Isn't Enough​

You've experienced SpecifyPlus's power in Chapters 30-32. The opinionated workflow works. But you've probably also noticed friction points:

Scenario: Your plan says "Use FastAPI 0.104.1 for the REST API."

What Happens: The agent suggests code using FastAPI 0.95.x syntax mixed with 0.104.x features because its training data contains both versions.

Result: 30 minutes debugging import errors and deprecated methods.

Tessl Solution: The Registry provides tessl/[email protected] usage spec with exact, version-specific API documentation.

The Future is Spec-Centric​

By the end of 2027, Guy Podjarny predicts developers won't look at code most of the time. They'll work at the specification level, with AI agents handling implementation details.

This chapter prepares you for that future by teaching you to marry SpecifyPlus's opinionated workflow with Tessl's infrastructure. Together, they create the most powerful specification-driven development system available today.

This is how you build production-grade software in the AI era.

This is how specifications become source code.

Let's begin.