Initial commit: AI conversation impact methodology and toolkit

CC0-licensed methodology for estimating the environmental and social
costs of AI conversations (20+ categories), plus a reusable toolkit
for automated impact tracking in Claude Code sessions.

impact-toolkit/README.md

@@ -0,0 +1,73 @@
+# Claude Code Impact Toolkit
+
+Track the environmental and financial cost of your Claude Code
+conversations.
+
+## What it does
+
+A PreCompact hook that runs before each context compaction, capturing:
+- Token counts (actual from transcript or heuristic estimate)
+- Cache usage breakdown (creation vs. read)
+- Energy consumption estimate (Wh)
+- CO2 emissions estimate (grams)
+- Financial cost estimate (USD)
+
+Data is logged to a JSONL file for analysis over time.
+
+## Install
+
+```bash
+# Project-level (recommended)
+cd your-project
+./path/to/impact-toolkit/install.sh
+
+# Or user-level (applies to all projects)
+./path/to/impact-toolkit/install.sh --user
+```
+
+Requirements: `bash`, `jq`, `python3`.
+
+## View results
+
+```bash
+.claude/hooks/show-impact.sh              # all sessions
+.claude/hooks/show-impact.sh <session_id> # specific session
+```
+
+## How it works
+
+The hook fires before Claude Code compacts your conversation context.
+It reads the conversation transcript, extracts token usage data from
+API response metadata, and calculates cost estimates using:
+
+- **Energy**: 0.003 Wh/1K input tokens, 0.015 Wh/1K output tokens
+- **PUE**: 1.2 (data center overhead)
+- **CO2**: 325g/kWh (US grid average for cloud regions)
+- **Cost**: $15/M input tokens, $75/M output tokens
+
+Cache-read tokens are weighted at 10% of full cost (they skip most
+computation).
+
+## Limitations
+
+- All numbers are estimates with low to medium confidence.
+- Energy-per-token figures are derived from published research on
+  comparable models, not official Anthropic data.
+- The hook only runs on context compaction, not at conversation end.
+  Short conversations that never compact will not be logged.
+- See `impact-methodology.md` for the full methodology, uncertainty
+  analysis, and non-quantifiable costs.
+
+## Files
+
+```
+impact-toolkit/
+  install.sh                       # installer
+  hooks/pre-compact-snapshot.sh    # PreCompact hook
+  hooks/show-impact.sh             # log viewer
+  README.md                        # this file
+```
+
+## License
+
+MIT. See LICENSE in the repository root.