# The API: what it is, and how to call it LLMS-Explorer as a service, not a website: what a key buys you, the REST surface, the hosted MCP gateway, the llmsx CLI, and where the free tier ends. Everything else in this section describes the llms.txt standard. This page describes the other half of the site: the hub's own tooling — lint, index, abstract, search — reached through an account instead of a terminal. ## What you're actually buying LLMS-Explorer is the concept-family-tree explorer with the hub's llms tooling hung off its nodes: lint or optimize an llms file, turn notes into one, abstract a concept out of a corpus, deepen it with a research wave, map its family. Reading is free everywhere on this site, with no account and no key — the reference, the blog, the directory, the public concept tree, and every served llms file (`/d/ /m/ /t/`). What a key buys is the tooling that spends model tokens or GPU time on your behalf: linting with the model passes, semantic search, indexing your own docset, publishing to the shared catalogue. One ledger records every token that gets spent; the plan you're on decides how far it goes before you hit a wall. See [Pricing](/billing/) for what each plan actually includes. ## Three ways in **Web.** Sign in with a passkey, GitHub, or Google at [/login/](/login/), then [/keys/](/keys/) to mint an API key and [/usage/](/usage/) to watch what it's spent. **REST API**, at `api.llms-explorer.com`. A key is `lx__` — shown once at creation, sent as a bearer token, scoped to what it's allowed to do: | Scope | Grants | |---|---| | `read` | Queries within your quota; read your own artifacts | | `run` | Create metered jobs — lint model passes, indexing, concept packs | | `publish` | Contribute to the shared catalogue | Routes worth knowing: `GET /api/usage` (ledger aggregates by component, model, day), `GET /api/billing/plans` (the price table, no sign-in needed), `GET/POST/DELETE /api/keys` (list, create with scopes, revoke). A metered call past your quota answers with a structured error naming the plan that would lift the limit, not a bare 402. **MCP**, hosted or local. The hub runs its own MCP server for tools you point at your own machine — semantic search, docset indexing, concept-tree queries — and it's unauthenticated by design, meant for `localhost` only. The **hosted** gateway is what puts that same tool surface behind a key without exposing the hub process itself: it terminates the session, resolves your key to an account, applies your plan's limits, and only then forwards the call over loopback. Five things it enforces that a bare tunnel wouldn't: 1. **Some tools aren't hosted at all.** `hub_ask`, `hub_distill_run`, and the hub's own memory and corpus tools are refused by name before your key's scopes are even checked — refused with the same message an unknown tool gets, so the hosted surface can't be enumerated by trying things. 2. **Your docsets are walled.** A docset key beginning `u_` belongs to exactly one account; arguments are checked going in and results are filtered coming back. 3. **A path is never just an argument.** Anything that names a file on the hub's own filesystem is resolved inside your own store — an unconfined path is a local-file-read primitive, so escaping your store is refused. 4. **One limit, one place.** Every quota comes from the same plan table `/billing/` describes; nothing is hardcoded in the gateway. 5. **A ledger row is written once**, after the hub confirms the work happened — not before (billing a failure) and not twice. Third-party full text is never served hosted, at any tier — a mirrored `llms-full.txt` you don't own stays on the hub, and the concept surface links out to the source instead. **CLI**, `llmsx`: `llmsx login`, `llmsx keys create --scopes read,run`, `llmsx usage [--month]`, `llmsx jobs `. See [Downloads](/downloads/) for install. ## The free tier's semantic search The free tier's semantic and hybrid search is a fixed 16-document demo, rate-limited and not billed — it's there to show what the retrieval looks like, not to serve your own corpus. Indexing your own docset, and querying it, both need a paid plan. The recorded three-leg run (keyword, vector, the fusion of both) is at [/demo/](/demo/) if you want to see the retrieval quality before paying for it. ## What's deterministic and free even with a key Not every tool call spends a token. Lint's deterministic passes — the ones that don't run a model — are free and unlimited-frequency-within-quota on every plan; only the *model* passes (P4/P8/P12) are metered. Keyword search (FTS5, no embedding call) is free up to a daily count that scales with your plan. The pattern throughout: cheap path first, deterministic before model, local Ollama before Claude — every metered step has a free deterministic shadow, and the lint that gates this site's own published files is exactly that free path.