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index-ai / Compare
Different problems, different tools — and they coexist. Here is exactly what index-ai does that llms.txt does not, so you can decide with specifics rather than vibes.
| index-ai | llms.txt | |
|---|---|---|
| What it is | A structured, open specification proposalMachine-readable JSON Schema, published and tested with the spec | A human-readable text fileMarkdown text with links, suggested by a blog post |
| Format | Valid JSON/.well-known/index-ai.json + /agent-index.json, both validated against the official JSON Schemas | Plain text / Markdown/llms.txt, no schema, no validation, no structure contract |
| Verification | Measured and checkedcontent_chars is an NFC code point count (exact or bounded max) verified against the served content; conformance is graded by a validator | Declared, never verifiednothing in the file is checked against the actual site content |
| Budget signal | Known before fetchevery measured node declares its content size (exact or max bound); the agent budgets tokens before fetching | Unknown until fetchedan agent must fetch each linked page to learn its size |
| Structure | Nodes + optional graphtyped relationships (2b) let agents traverse without parsing HTML | Flat list of linkssections and links, no data model, no relationships |
| Query interface | Level 3 (MCP)an optional typed API over the Agent View | Nonea text file, no query interface defined |
| Policy | Machine-readablepolicy.usage_preferences declares search/summarization/citation preferences | Absentno machine-readable usage or citation policy |
The one-line difference
llms.txt tells an agent what links exist; index-ai tells an agent what content exists, how big it is, how it is structured, and how to query it — measured and verifiable.
Yes — index-ai is additive. Implementing index-ai MUST NOT require changes to your existing robots.txt, sitemap.xml, or llms.txt. You can run all of them at once; they solve different problems:
Same origin — four conventions, one job each.
All four sit on the same origin, side by side. index-ai is the only one that is measured and machine-queryable.
Not a replacement, not a fork
index-ai is a distinct, deliberate convention — not an llms.txt variant. It even offers an optional bridge: an llms.txt file may point to the index-ai manifest. The normative statement lives in §16 Compatibility of the specification.
The AI-readiness walkthrough — the Agent View in action.