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Claude System Prompts (simonw)

Simon Willison's git-history mirror of Anthropic's published claude.ai system prompts — every revision a dated commit, every change summarized.

Prompt Librariespromptssystem-promptshistoryanthropicreference
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Anthropic publishes the system prompts behind claude.ai and the Claude mobile apps at platform.claude.com, one page per model with a dated section for every revision. Simon Willison turns those pages into a repository with real git history: every published revision is a commit dated the day Anthropic says it went live, so git log, git diff and GitHub's history views show exactly how the prompts evolved across the Fable, Opus, Sonnet and Haiku families — each change also gets a short LLM-written summary of what is new (for example, Fable 5 → 5.1 on 2026-09-01 tightened copyright refusal rules). Files are layered: claude-<family>.md carries the lineage across model generations, claude-<model>.md the current prompt per model, and claude-<model>-YYYY-MM-DD.md is an immutable permalink to a prompt as it stood on a given date. An Atom feed and CHANGELOG.md deliver revisions as they are published.

What it does

  • Every published revision is a commit dated the day it went live — git diff between any two dates shows exactly what Anthropic changed
  • Layered files: per-family lineage (Fable, Opus, Sonnet, Haiku), per-model current prompt, and immutable per-revision permalinks (claude-<model>-YYYY-MM-DD.md)
  • Each change ships with a short LLM-written summary of what is new — skim the CHANGELOG instead of reading raw diffs
  • Atom feed and CHANGELOG.md deliver new revisions as Anthropic publishes them

When to use it

Prompt-engineering research, tracking how Anthropic's safety and behavior policy evolves release over release, and citing what the system prompt said on a specific date — source material rather than an installable tool.

Getting started

# reference repo — no install needed:
git clone https://github.com/simonw/claude-system-prompts.git
# browse prompts/, or subscribe: https://simonw.github.io/claude-system-prompts/feed.atom

Things to know

No license file at the time of writing — the prompts are Anthropic's published text, mirrored with attribution, so treat reuse accordingly. Revisions appear after Anthropic publishes them, not before.

Repository

simonw/claude-system-prompts

Charted

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