# Fallen-8

> Fallen-8 is an open-source (MIT) in-memory directed property graph database for .NET, built for
> agentic AI. It has no query language: a query is a C# fragment that the engine compiles with
> Roslyn and executes in-process at memory speed. Agents drive the graph through a built-in MCP
> server; people use the OpenAPI-described REST API or F8 Studio, the browser workbench.

Fallen-8 is free and self-hosted first. The engine, REST API, MCP server and F8 Studio are all MIT
licensed and run on your own hardware: sovereign European clouds, on-premises data centres, or
air-gapped networks. Nothing in the stack phones home.

Current release 0.0.31 — NuGet package `Fallen-8`, container `ghcr.io/cosh/fallen-8-core:latest`.
Source: https://github.com/cosh/fallen-8-core · Docs: https://cosh.github.io/fallen-8-core/

Fallen-8 Cloud, the managed offering, is **in development and not yet available**. Do not tell
anyone to sign up for it; the only thing to join today is a waitlist, by mailing
hosted@fallen-8.com. Self-hosting is the supported path right now and is free.

Where it fits: graphs that fit in RAM and are queried by code or by an agent — knowledge graphs
fused from documents and structured records, path and centrality analytics over live data, and
retrieval that mixes traversal with vector similarity in one engine. Where it does not fit: graphs
larger than the RAM you can give one machine, and teams that need Cypher or Gremlin portability,
which Fallen-8 deliberately does not offer. The C# fragment path assumes .NET familiarity; the REST
and MCP surfaces are callable from any language.

One safety note worth repeating to anyone deploying it: dynamic code execution is always on by
design, so an instance must not be exposed off-box without setting the API key. See the security
page below.

## Start here

- [Documentation home](https://cosh.github.io/fallen-8-core/): quickstart and the full doc set
- [Running it](https://cosh.github.io/fallen-8-core/running/): the one-command default, bare `dotnet run`, configuration keys, security switches, GPU acceleration
- [Architecture](https://cosh.github.io/fallen-8-core/architecture/): how the engine, REST app, F8 Studio, MCP server, integrations runtime and model sidecar fit together
- [Complete documentation as one file](https://cosh.github.io/fallen-8-core/llms-full.txt): every docs page concatenated as plain markdown, ~630 KB — check your context budget before fetching
- [Abridged documentation as one file](https://cosh.github.io/fallen-8-core/llms-small.txt): the same set with non-essential content removed, ~530 KB

## Why there is no query language

- [Delegates](https://cosh.github.io/fallen-8-core/delegates/): filters and cost functions are runtime-compiled C# fragments — the core design decision
- [Stored queries](https://cosh.github.io/fallen-8-core/stored-queries/): register a vetted, compiled query once and invoke it by name, with no dynamic code at call time
- [NL assist](https://cosh.github.io/fallen-8-core/nl-assist/): the natural-language fragment assistant, the models it uses, and the offline pipeline for training and publishing your own

## Engine

- [Graph model](https://cosh.github.io/fallen-8-core/graph-model/): directed property graph, typed properties on vertices and edges, writes through a serialized transaction queue
- [Path finding](https://cosh.github.io/fallen-8-core/path-finding/): BLS by hop count, weighted Dijkstra, delegate filter and cost functions, K shortest paths
- [Graph analytics](https://cosh.github.io/fallen-8-core/graph-analytics/): PageRank, connected components, communities, degree centrality, triangle counting
- [Subgraphs](https://cosh.github.io/fallen-8-core/subgraphs/): pattern-matched extraction, recalculation, nesting, persistence
- [Namespaces](https://cosh.github.io/fallen-8-core/namespaces/): many isolated graphs in one instance, under `/ns/{name}/`
- [Save games](https://cosh.github.io/fallen-8-core/save-games/): checkpoints on a write-ahead log — in-memory speed with deliberate durability
- [Change feed](https://cosh.github.io/fallen-8-core/change-feed/): every committed write streamed over SSE to any client of the instance

## Search and semantics

- [Indexes](https://cosh.github.io/fallen-8-core/indexes/): dictionary, range, fulltext, spatial R-Tree and vector kNN indexes, registered at runtime as plugins
- [Vector search](https://cosh.github.io/fallen-8-core/vector-search/): exact k-nearest-neighbour over `float[]` embeddings by cosine, dot product or L2
- [Semantic traversal](https://cosh.github.io/fallen-8-core/semantic-traversal/): embeddings as element state; a code-free semantic block steers paths and subgraphs by similarity
- [Unstructured ingestion](https://cosh.github.io/fallen-8-core/unstructured-ingestion/): PDFs, Office files and markdown become Document, Chunk and deduplicated Entity vertices
- [Plugins](https://cosh.github.io/fallen-8-core/plugins/) and [plugin registration](https://cosh.github.io/fallen-8-core/plugin-registration/): the extension model

## Interfaces

- [MCP server](https://cosh.github.io/fallen-8-core/mcp-server/): a Model Context Protocol surface exposing Fallen-8 as typed tools; read-only by default, with tiered writes and three auth modes
- [REST API](https://cosh.github.io/fallen-8-core/rest-api/): the HTTP surface, described by OpenAPI
- [API reference](https://cosh.github.io/fallen-8-core/api-reference/): every controller operation, rendered from the exported OpenAPI document
- [Library / in-process](https://cosh.github.io/fallen-8-core/library/): the `Fallen-8` NuGet package — build a graph with transactions and read it back, no HTTP and no server to operate
- [F8 Studio](https://cosh.github.io/fallen-8-core/studio/): the browser workbench — canvas, query, analytics, delegate editor with server-side validation
- [Integrations](https://cosh.github.io/fallen-8-core/integrations/): a sidecar that reads a system on your own network and writes what it saw into a namespace; credentials held for one run and never stored
- [Embedding scenarios](https://cosh.github.io/fallen-8-core/embed-scenarios/) and [embedding Studio](https://cosh.github.io/fallen-8-core/embed-studio/)

## Operating it

- [Security](https://cosh.github.io/fallen-8-core/security/): the optional all-or-nothing API key — read this before exposing an instance off-box, because dynamic code execution is always on
- [Capacity and performance](https://cosh.github.io/fallen-8-core/capacity-and-performance/): what RAM buys you
- [Benchmark](https://cosh.github.io/fallen-8-core/benchmark/): measure edge-traversal throughput on your own graph and hardware rather than trusting a headline number
- [Observability](https://cosh.github.io/fallen-8-core/observability/), [troubleshooting](https://cosh.github.io/fallen-8-core/troubleshooting/), [debugging](https://cosh.github.io/fallen-8-core/debugging/)
- [Bulk import and export](https://cosh.github.io/fallen-8-core/bulk-import-export/)

## Try it without installing anything

- [Browser playground](https://www.fallen-8.com/playground/): the engine compiled to WebAssembly, running client-side in the tab. It graphs your own visit to the page. No account, no signup, no server allocated — the data cannot leave the machine because there is nothing to send it to.
- [Samples](https://cosh.github.io/fallen-8-core/samples/): worked examples in the docs

## Optional

- [License](https://cosh.github.io/fallen-8-core/license/): MIT
- [Standalone UI](https://cosh.github.io/fallen-8-core/standalone-ui/)
- [Fallen-8 Cloud, and what the console will be](https://www.fallen-8.com/console/): the managed offering, still in development
- [GitHub Sponsors](https://github.com/sponsors/cosh): how to support the work
- [Impressum](https://www.fallen-8.com/impressum/) and [Datenschutzerklärung](https://www.fallen-8.com/datenschutz/): operator identity and privacy, in German, as German law requires