{"slug": "i-measured-what-it-costs-an-ai-agent-to-read-my-obsidian-vault-a-derived-index", "title": "I measured what it costs an AI agent to read my Obsidian vault — a derived index made it ~150x cheaper", "summary": "A developer measured the context cost of AI coding agents reading an entire Obsidian vault and found that a generated index map reduced context usage by roughly 150x. The approach uses a script to create a one-line-per-note summary, a ranking system, and an AGENTS.md file to govern agent behavior. The developer packaged the method as a $15 template.", "body_md": "I keep a plain Obsidian vault — about 1.4 MB of markdown across notes, projects and an inbox — and I let coding agents (the Claude Code / Cursor kind) work inside it: searching, summarizing, drafting. The first thing I measured changed how I set all of this up: **an agent that reads the whole vault isn't being thorough. It's drowning.**\n\nEvery file it opens costs context. Read enough files and the actual question gets buried under files that were never relevant. Three boring fixes, each measured on my own setup:\n\nA small script walks the vault and writes one line per note: title, what it's about, size, last change. That map is ~9 KB standing in for ~1.4 MB — the same answer to \"what exists here and where,\" for about **150× less context**. It's generated, never hand-maintained: I rerun the script after heavy edits, because a stale map is worse than none — it asserts confidently things that stopped being true.\n\nMeasured cost per question on my setup:\n\nMost questions die on the second rung and never pay the 35 KB. The specific tools don't matter; the point is that \"just read everything\" is the most expensive possible answer to most questions.\n\nReading is free; writing is gated. A plain `AGENTS.md`\n\nat the vault root states it: the index is the front door, the agent may read anything, and it writes nothing without asking — with folder ownership explicit (my notes vs. a staging area it may use). This is the piece that stops an assistant from quietly reorganizing your knowledge base overnight.\n\nPart 1 is an afternoon of Python (walk the folder, pull first heading + gist + size + modified date, one line per note). Part 2 done well is the fiddly one — ranking by term rarity and returning section trails took real iteration to stop returning junk. Part 3 is one text file.\n\n**Full disclosure:** I ended up packaging all of this — the vault starter (notes/people/projects/inbox with example notes teaching each folder's pattern), the two tools, the rules file, a 10-minute tutorial and a short ebook on the method, including a what-NOT-to-do section — as a US$15 one-time template. It's my product; the link is below. The three ideas above work fine with nothing but your own scripts — build your own index and you're 90% there.\n\n[Second Brain Starter — US$15 one-time](https://oroborolabs.gumroad.com/l/ikkpfm)\n\nHappy to answer questions about the measurement method, or about where this approach breaks.\n\n*Cross-posted from Oroboro Labs — this post is the canonical version; the original carries the full method notes.*", "url": "https://wpnews.pro/news/i-measured-what-it-costs-an-ai-agent-to-read-my-obsidian-vault-a-derived-index", "canonical_source": "https://dev.to/oroborolabs/i-measured-what-it-costs-an-ai-agent-to-read-my-obsidian-vault-a-derived-index-made-it-150x-34ca", "published_at": "2026-08-29 12:07:54+00:00", "updated_at": "2026-08-29 12:49:01.550641+00:00", "lang": "en", "topics": ["ai-agents", "developer-tools", "ai-infrastructure"], "entities": ["Obsidian", "Claude Code", "Cursor", "Oroboro Labs"], "alternates": {"html": "https://wpnews.pro/news/i-measured-what-it-costs-an-ai-agent-to-read-my-obsidian-vault-a-derived-index", "markdown": "https://wpnews.pro/news/i-measured-what-it-costs-an-ai-agent-to-read-my-obsidian-vault-a-derived-index.md", "text": "https://wpnews.pro/news/i-measured-what-it-costs-an-ai-agent-to-read-my-obsidian-vault-a-derived-index.txt", "jsonld": "https://wpnews.pro/news/i-measured-what-it-costs-an-ai-agent-to-read-my-obsidian-vault-a-derived-index.jsonld"}}