# Ceisium

> Ceisium builds practical software for teams and agents that need to use public knowledge through clear, programmable interfaces.

## Ceisium Search

Ceisium Search turns public websites into project-scoped search indexes with managed crawling and an authenticated Search API.

When to use Ceisium Search:
- Use Ceisium Search when a team needs search across documentation, guides, pricing, changelogs, blog posts, or other public website pages.
- Use Ceisium Search when a team wants managed crawling and practical relevance defaults instead of operating its own search stack.
- Use the Ceisium Search API when a website or trusted backend needs programmatic ranked results from one project.
- Do not use Ceisium Search to index secrets or private content without a separate approved security design.
- Search remains authenticated. Use Browser/public keys only with allowed origins and Server keys only in trusted backend code.

## Start here

- [Ceisium Search documentation](https://ceisium.com/docs/index.md): Setup, crawling, indexing, Search API, usage, and analytics.
- [About Ceisium](https://ceisium.com/about/index.md): Company purpose, first product, principles, and founder.
- [Ceisium Search pricing](https://ceisium.com/pricing/index.md): Current plans, quotas, and usage notes.

## API and integration

- [Developer resources](https://ceisium.com/developers/index.md): API contract, authentication, examples, and capability discovery.
- [OpenAPI 3.1 contract](https://ceisium.com/openapi.json): Typed operations, request and response schemas, errors, and bearer authentication.
- [API capabilities](https://api.ceisium.com/v1/capabilities): Public JSON discovery for supported API endpoints.
- [Quickstart](https://ceisium.com/docs/index.md): Create a project, crawl it, query the API, and embed search.
- [Search API](https://ceisium.com/docs/search-api/index.md): Auth, request fields, response shape, result limits, errors, and examples.
- [UI Components](https://ceisium.com/docs/ui-components/index.md): Install search UI patterns and wire them to a Ceisium Search project.
- [Analytics](https://ceisium.com/docs/analytics/index.md): Read search events, no-result queries, popular queries, and engagement.
- [Crawl Logs](https://ceisium.com/docs/crawl-logs/index.md): Track crawl status, page outcomes, failures, retries, and coverage.
- [Usage](https://ceisium.com/docs/usage/index.md): Review API requests, crawl volume, indexing usage, and plan limits.

## Trust and company

- [Contact Ceisium](https://ceisium.com/contact/index.md): Product, support, billing, security, and privacy contact.
- [Privacy policy](https://ceisium.com/privacy/index.md): Data categories, purposes, providers, retention, cookies, rights, and contact.
- [Terms of Service](https://ceisium.com/terms/index.md): Accounts, content duties, acceptable use, Search keys, billing, service changes, and limits.
- [Sitemap](https://ceisium.com/sitemap.xml): Complete public page discovery.

## Public site pages

- [Blog | Ceisium](https://ceisium.com/blog/index.md): Ceisium Blog notes on website search, crawl quality, relevance, and keeping public product content easy to find as your site changes.
- [Changelog | Ceisium](https://ceisium.com/changelog/index.md): Ceisium product updates, launch notes, and improvements across website search, docs, crawl quality, and the app experience.

## Optional

- [Full agent context](https://ceisium.com/llms-full.txt): Expanded product, API, safety, trust, and current public content.
- [Ceisium Search Agent Skill](https://ceisium.com/skill.md): Installable capability and workflow instructions for coding agents.
- [Introducing Ceisium Search](https://ceisium.com/changelog/first-release/index.md): Search that tunes itself as your site changes.
- [BM25 in RAG: Why Exact Keywords Still Matter](https://ceisium.com/blog/bm25-in-rag/index.md): Dense retrieval can miss error codes, identifiers, and exact phrases. BM25 gives RAG systems another path to the source evidence they need.
- [Boolean Retrieval: AND, OR, and NOT in Search](https://ceisium.com/blog/boolean-retrieval/index.md): Learn how Boolean search uses AND, OR, and NOT to combine result sets, where exact control helps, and why website search still needs ranking.
- [Document Length Normalization: Why Long Pages Need Context](https://ceisium.com/blog/document-length-normalization/index.md): Learn why long pages get more chances to match a search query, how BM25 adjusts for relative document length, and why shorter is not automatically better.
- [How Website Crawling Shapes Search Quality](https://ceisium.com/blog/how-website-crawling-shapes-search-quality/index.md): Learn how crawl scope, sitemaps, rendering, URL identity, and recrawl freshness shape the pages a site-search ranker can choose from.
- [Semantic Search vs Keyword Search: How to Choose and When to Combine Them](https://ceisium.com/blog/semantic-search-vs-keyword-search/index.md): Keyword search uses literal evidence. Embedding-based semantic search bridges vocabulary gaps. Learn where each fails and when hybrid retrieval earns its added complexity.
- [TF-IDF: The Search Ranking Idea Behind BM25](https://ceisium.com/blog/what-is-tf-idf/index.md): TF-IDF is a classic lexical ranking method that scores documents using repeated query words and rare query words. Learn how it works, where it helps, and how BM25 addresses some of its limits.
- [What Is an Inverted Index?](https://ceisium.com/blog/what-is-an-inverted-index/index.md): An inverted index maps terms to the documents that contain them, helping search engines find text matches without scanning every page.
- [What is BM25? A Plain English Guide](https://ceisium.com/blog/what-is-bm25/index.md): BM25 is a keyword search ranking function that scores documents using term frequency, term rarity, and document length. Learn how it works, where it helps, and how it differs from TF-IDF.
- [What Is Hybrid Search?](https://ceisium.com/blog/what-is-hybrid-search/index.md): Hybrid search combines keyword and vector retrieval. Learn how fusion, candidate windows, filters, and reranking turn two result lists into one.
- [What is Inverse Document Frequency?](https://ceisium.com/blog/what-is-inverse-document-frequency/index.md): Inverse document frequency helps search rank rare query words above words that appear everywhere. Learn the idea with a simple docs-search example.
- [What Is Tokenization in Search?](https://ceisium.com/blog/what-is-tokenization-in-search/index.md): Learn how search engines split and normalize page text and queries into searchable terms, and why those choices can decide which pages reach ranking.
- [What Is Vector Search?](https://ceisium.com/blog/what-is-vector-search/index.md): Vector search finds related content by comparing embeddings. Learn how vectors, similarity, approximate nearest-neighbor search, and hybrid retrieval work together.