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Public story · 2026-03-15 · source-backed
Three independent sources — Simon Willison at the Pragmatic Summit, blog.tedivm.com's coding agent guide, and Anthropic's 2026 Trends Report — converged in March 2026 on the same conclusion: the highest-leverage skill in AI-assisted development is no longer prompt engineering but specification engineering. Define scope, constraints, acceptance criteria, and architectural boundaries in a structured brief before any AI is invoked. Each AI-generated feature goes on its own branch with the spec as the review baseline. blog.tedivm.com
This isn't just a workflow suggestion — it's the emerging consensus for why some teams ship reliably with agents while others drown in verification debt. Willison's fireside chat framed it as "conformance-driven development": write the test, write the spec, then let the agent implement against both. simonwillison.net The spec becomes the contract the agent must satisfy, not a suggestion it can interpret creatively.
Addy Osmani's PEV loop (Plan → Execute → Verify) formalizes the same pattern: humans define goals and constraints, agents plan and execute, humans review output as a junior engineer's PR — never as a trusted commit. Addy Osmani Boris Cherny, the Anthropic engineer who built Claude Code, uses a CLAUDE.md structured around six operational areas — plan mode defaults, subagent delegation, verification requirements, elegance checks — all under 300 lines, writing only what Claude would get wrong without the file. Glen Rhodes
The pattern is clear: front-load specification, keep agent context lean, verify against the spec. Everything else is commentary.
Each link below shares sources, entities, or timing with this story.
Simon Willison uses Claude Code / Shared entities / Shared topic / Earlier coverage
Linked by a graph relationship (Simon Willison uses Claude Code); both cover Anthropic, Claude Code, Execute, PEV; overlapping topics (anthropic, claude, plan).
Simon Willison uses Claude Code / Shared entities / Shared topic / What happened next
Linked by a graph relationship (Simon Willison uses Claude Code); both cover Anthropic, Boris Cherny, Claude, Claude Code; overlapping topics (agent, anthropic, claude).
Boris Cherny works at Anthropic / Shared entities / Same source domain / Shared topic / What happened next
Linked by a graph relationship (Boris Cherny works at Anthropic); both cover Addy Osmani, Anthropic, Boris Cherny, Simon Willison; reported by the same outlet (simonwillison.net).
Simon Willison uses Claude Code / Shared entities / Same source domain / What happened next
Linked by a graph relationship (Simon Willison uses Claude Code); both cover Anthropic, Claude, Claude Code, Simon Willison; reported by the same outlet (simonwillison.net).
Simon Willison uses Fable / Shared entities / Same source domain / Shared topic / What happened next
Linked by a graph relationship (Simon Willison uses Fable); both cover Anthropic, Claude Code, Simon Willison, Willison; reported by the same outlet (simonwillison.net).
Simon Willison uses Claude Code / Shared entities / Shared topic / What happened next
Linked by a graph relationship (Simon Willison uses Claude Code); both cover Addy Osmani, Anthropic, Boris Cherny, Claude Code; overlapping topics (agent, anthropic, engineer, engineering).
Simon Willison uses Fable / Shared entities / Same source domain / Shared topic / What happened next
Linked by a graph relationship (Simon Willison uses Fable); both cover Anthropic, CLAUDE, Claude Code, Simon Willison; reported by the same outlet (simonwillison.net).
Simon Willison released LLM / Shared entities / Same source domain / Shared topic / What happened next
Linked by a graph relationship (Simon Willison released LLM); both cover Addy Osmani, Claude, Claude Code, March; reported by the same outlet (addyosmani.com).