Everruns Framework and advanced hosts

Start new Rust applications with the application-facing everruns Framework. Its default build runs offline with no database, server, worker, network, or credentials:

cargo add everruns

use everruns::{Agent, InMemoryEngine, Model};

# async fn example() -> Result<(), Box<dyn std::error::Error>> {
let agent = Agent::builder()
    .instructions("Answer in one short sentence.")
    .model(Model::simulated("Hello from Everruns."))
    .build()?;
let turn = InMemoryEngine::new().create(agent).run("Say hello.").await?;
assert_eq!(turn.response, "Hello from Everruns.");
# Ok(())
# }

Choose the dependency path

• Ordinary applications use everruns for agents, models/providers, tools, sessions, events, cancellation, workspaces, MCP, plugins, inspection, and opt-in local scheduling.
• Advanced system integrators combine everruns with everruns-host and focused siblings such as everruns-mcp, provider crates, and integration crates. They import HostBackends and host phase contracts directly.

everruns-host is the only low-level host boundary; there is no separate runtime crate.

Common Framework tasks

• Use Model::simulated or Model::simulated_with_config for deterministic, credential-free tests.
• Pair a plain Framework Model with Provider, or use a provider convenience, for real models.
• Add ordinary tools with #[everruns::tool] or FunctionTool; use the curated everruns::capability API for reusable capability packages.
• Observe Session::events, cancel through RunOptions, and inspect the next model context with Session::inspect.
• Seed files with AgentBuilder::file and readonly_file; attach one trusted workspace and configure WorkspacePolicy where needed.
• Configure scoped MCP through McpServer and plugins through AgentBuilder::plugin. Local-process MCP stays opt-in.
• Enable everruns/local for a real workspace plus local task/schedule state. The same profile also provides crash-durable canonical event history.

Advanced host boundary

Use low-level crates only when the application is itself an execution host and must replace stores, filesystem factories, platform definitions, phase adapters, durable scheduling lifecycle, or worker topology:

cargo add everruns everruns-host everruns-provider

use everruns::Provider;
use everruns_host::{HostBackends, InProcessRuntimeBuilder};
use everruns_provider::model_spec::ModelSpec;
# let _ = (HostBackends::in_memory, InProcessRuntimeBuilder::new);

Canonical events are the only maintained conversation write path. Advanced hosts use EventLog, EventHistory, EventSink, and EventReader; legacy mutable-history paths are not execution inputs.

References

• Everruns Framework
• Custom backends
• Framework API
• Host API
• Focused crate catalog
• Domain-language glossary