--- title: "Glossary: terms for what agents read: Agent Ready HTML" description: "40 terms for what an agent reads: initial HTML, plain fetch, soft 404, llms.txt, markdown negotiation, JSON-LD and OpenAPI, each with a sourced example." canonical: https://agentreadyhtml.com/glossary/ site: "Agent Ready HTML" last_updated: 2026-11-04 section: "Glossary" --- # Glossary: terms for what agents read: Agent Ready HTML > 40 terms for what an agent reads: initial HTML, plain fetch, soft 404, llms.txt, markdown negotiation, JSON-LD and OpenAPI, each with a sourced example. Source: https://agentreadyhtml.com/glossary/ Site: Agent Ready HTML Last reviewed: 2026-11-04 # Glossary In short 40 terms used on this site, each defined in a sentence or two and followed by a sourced, dated example. They run from initial HTML and plain fetch through soft 404, llms.txt, markdown negotiation and JSON-LD to answer provenance and token reduction. Each term has its own page. Crawl edition 2026-11-04, page updated 2026-11-04. [How the viewer, the index and the scores work](https://agentreadyhtml.com/method/). [Accept header](https://agentreadyhtml.com/glossary/accept-header/) The request header that lists media types a client will take, with optional q weights. [AFDocs](https://agentreadyhtml.com/glossary/afdocs/) The Agent-Friendly Documentation spec and its open-source checker, used by Mintlify, ReadMe and GitBook docs scores. [Agent 404](https://agentreadyhtml.com/glossary/agent-404/) A 404 response written for agents, often markdown, that links the index and similar pages so the agent can recover. [Agent score (docs)](https://agentreadyhtml.com/glossary/docs-agent-score/) A docs-specific readiness score computed from AFDocs-style checks, published by docs vendors. [Agent-optimised mirror](https://agentreadyhtml.com/glossary/agent-mirror/) A separate version of pages served only to AI user agents at the same URLs. [agents.md](https://agentreadyhtml.com/glossary/agents-md/) On Shopify, the canonical agent-discovery document of a store, mirrored at /llms.txt and /llms-full.txt. [Answer provenance](https://agentreadyhtml.com/glossary/answer-provenance/) Which fetched page an agent answer can be traced to. [App shell](https://agentreadyhtml.com/glossary/app-shell/) A near-empty HTML document whose content is injected by JavaScript after load, typically a single div with id root or app. [Content negotiation](https://agentreadyhtml.com/glossary/content-negotiation/) The HTTP mechanism where the client states preferred formats in the Accept header and the server picks a representation for the same URL. [Content-Signal](https://agentreadyhtml.com/glossary/content-signal/) A declaration of permitted AI uses (ai-train, search, ai-input), sent as a robots.txt line or a response header. [Edge conversion](https://agentreadyhtml.com/glossary/edge-conversion/) Turning origin HTML into another format at the CDN, without changing the origin. [Fenced code block](https://agentreadyhtml.com/glossary/fenced-code-block/) Code set off by triple backticks with a language tag, so agents can separate code from prose. [File list](https://agentreadyhtml.com/glossary/file-list/) An H2 section in llms.txt holding a markdown list of links in the form \[name\](url), optionally followed by a colon and notes. [HTTP Link header](https://agentreadyhtml.com/glossary/http-link-header/) A response header carrying link relations (RFC 8288), so a CDN can advertise files without changing markup. [Hydration](https://agentreadyhtml.com/glossary/hydration/) The step where client JavaScript attaches event handlers to server-rendered HTML. The content is already present before it happens. [Initial HTML](https://agentreadyhtml.com/glossary/initial-html/) The HTML document a server returns for a URL before any JavaScript runs. A plain-fetch agent reads only this, so the answer has to be in it. [JSON-LD](https://agentreadyhtml.com/glossary/json-ld/) Structured data written as JSON in a script tag of type application/ld+json, using schema.org types. [Lighthouse llms.txt audit](https://agentreadyhtml.com/glossary/lighthouse-llms-txt-audit/) A Chrome Lighthouse check in the Agentic Browsing category that flags a server error on /llms.txt and marks a 404 as not applicable. [Linked arrival](https://agentreadyhtml.com/glossary/linked-arrival/) A fetch of a machine file that followed a link rather than a guessed path. [llms-full.txt](https://agentreadyhtml.com/glossary/llms-full-txt/) A companion file, not defined in the llmstxt.org text, that concatenates the full markdown of a site in one document. [llms.txt](https://agentreadyhtml.com/glossary/llms-txt/) A markdown file at /llms.txt that names a site, summarises it and lists links to LLM-friendly pages. Only the H1 is required. [Markdown negotiation](https://agentreadyhtml.com/glossary/markdown-negotiation/) Content negotiation where Accept: text/markdown returns the page as markdown with Content-Type text/markdown. [Markdown twin](https://agentreadyhtml.com/glossary/markdown-twin/) A markdown copy of a page at a predictable URL, such as page.md or page.html.md. [OpenAPI](https://agentreadyhtml.com/glossary/openapi/) A machine-readable description of an HTTP API, usually openapi.json or openapi.yaml. [Optional section](https://agentreadyhtml.com/glossary/optional-section/) An H2 named Optional in llms.txt that holds secondary links. v2 keeps it as a convention and drops its special meaning for tools. [Plain fetch](https://agentreadyhtml.com/glossary/plain-fetch/) An HTTP GET that reads the response body without executing scripts, the way most agent web tools and curl read pages. [Prerendering](https://agentreadyhtml.com/glossary/prerendering/) Rendering pages to static HTML at build time so every request gets finished content. [Real status code](https://agentreadyhtml.com/glossary/real-status-code/) An HTTP status that matches what happened: 200 for a page, 404 for a missing path, 429 for throttling. AgentReady makes this a MUST. [rel="alternate" type="text/markdown"](https://agentreadyhtml.com/glossary/rel-alternate-markdown/) A link relation in HTML or an HTTP Link header that points from a page to its markdown version. Added to llms.txt v2. [rel="describedby"](https://agentreadyhtml.com/glossary/rel-describedby/) A link relation that points from a page to the llms.txt file covering it. Added in llms.txt v2. [Rendered HTML](https://agentreadyhtml.com/glossary/rendered-html/) The DOM after a browser has run the page scripts. A human and a JavaScript-running agent see it; a plain-fetch client does not. [schema.org](https://agentreadyhtml.com/glossary/schema-org/) The shared vocabulary of types and properties (Organization, Product, TechArticle) used in JSON-LD. [Server Components](https://agentreadyhtml.com/glossary/server-components/) React components that render on the server; the default for pages and layouts in the Next.js App Router. [Server-side rendering (SSR)](https://agentreadyhtml.com/glossary/server-side-rendering/) Rendering a page to HTML on the server per request, so the response carries the content. [Soft 404](https://agentreadyhtml.com/glossary/soft-404/) A missing page that returns 200 with an error message in the body. Agents and crawlers cannot tell it from a real page. [Subpath llms.txt](https://agentreadyhtml.com/glossary/subpath-llms-txt/) An llms.txt below the root that covers the pages under its path; v2 says the most specific file applies. [Token reduction](https://agentreadyhtml.com/glossary/token-reduction/) How many fewer model tokens a page costs as markdown than as HTML. [Universal rendering](https://agentreadyhtml.com/glossary/universal-rendering/) Nuxt term for rendering on the server first and hydrating in the browser. [Vary: Accept](https://agentreadyhtml.com/glossary/vary-accept/) A response header telling caches that the body depends on the Accept header, so HTML and markdown are stored separately. [x-markdown-tokens](https://agentreadyhtml.com/glossary/x-markdown-tokens/) A response header Cloudflare adds with the estimated token count of the markdown body. ## Sources 1. [llms.txt proposal (llmstxt.org)](https://llmstxt.org/) https://llmstxt.org/, read 4 November 2026 Last reviewed 4 November 2026