Anthropic Skills guide formalizes structured execution design over prompt engineering for Claude agents
Anthropic Just Formalized What Good Agent Builders Already Knew
Anthropic published a 30-page guide on building Skills for Claude, and I think the framing matters more than the technical details inside it. They’re not calling this prompt engineering. They’re calling it execution design. That shift in language is deliberate, and it reflects something real about where agent development is heading.
What a Skill Actually Is
A Skill is not a clever prompt. It’s a structured system with a SKILL.md file at its core, optionally bundled with scripts, reference files, and assets. You define a repeatable workflow once, and Claude runs it consistently whether you’re working in Claude, Claude Code, or the API. Build once, use everywhere.
The structural choice that caught my attention is what Anthropic calls progressive disclosure. Lightweight YAML frontmatter tells Claude when a skill is relevant. Full instructions only load when triggered. Additional files only load if the task actually requires them. Context is treated as a finite resource to be rationed carefully, not a bucket you fill to the top and hope for the best.
That’s a meaningful architectural opinion, and I agree with it. Most agent failures I’ve seen come from context mismanagement, not from the model being incapable.
The MCP Analogy Is Surprisingly Good
The guide draws a clean distinction: MCP gives Claude the kitchen, Skills give it the recipe.
Without Skills, a user connects tools and stares at a blank screen wondering what to do next. With Skills, workflows trigger automatically, best practices are already embedded in the execution path, and API calls become consistent instead of ad hoc. The analogy works because it captures the dependency clearly. Tools without workflows are just potential energy.
Three Patterns Worth Building Around
Anthropic outlines three major implementation patterns in the guide: document and asset creation, workflow automation, and MCP enhancement. None of these are surprising on their own, but seeing them formalized with specific file structures and trigger logic is useful. It gives teams a common vocabulary and a starting point that isn’t just “write a system prompt and hope.”
The Testing Section Is the Most Underrated Part
Most agent builders I know treat testing as an afterthought. Anthropic does not. The guide calls out four specific metrics worth tracking: trigger accuracy, tool call efficiency, failure rate, and token usage. That list is practical and concrete. Trigger accuracy alone is worth obsessing over. If a Skill fires at the wrong time, everything downstream breaks regardless of how well the instructions are written.
This is where “execution design” earns its name. You’re not optimizing a prompt. You’re measuring a system.
My Honest Take
I’ve been skeptical of the “prompt engineering is dead” framing that circulates every few months. Usually it’s overblown. This time I think something real is happening. The Skills architecture formalizes patterns that good builders have been using informally for a while: modular instructions, conditional loading, explicit trigger conditions, consistent testing. What Anthropic did is give those patterns a name and a spec.
That matters for teams, not just solo builders. Shared vocabulary reduces the time you spend arguing about implementation and increases the time you spend actually building. If your organization is deploying Claude agents at any real scale, this guide is worth reading in full and treating as a design reference, not just marketing material.
The era of “just write a better prompt” was always going to end. The question was what would replace it. Structured execution design is a reasonable answer.
Sources & Further Reading
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