State vs Resources

You have two ways to store data in flow-state.dev: scope state and resources. Both live on the same scopes (session, user, project), both use atomic operations, and both are invisible to clients without clientData. They serve different purposes.

Scope state

A flat, typed object on each scope. Blocks read and write fields directly:

const modeSwitch = handler({
  name: "mode-switch",
  sessionStateSchema: z.object({ mode: z.enum(["chat", "agent"]).default("chat") }),
  execute: async (input, ctx) => {
    await ctx.session.patchState({ mode: "agent" });
    return input;
  },
});

Good for: mode flags, counters, configuration values, status indicators. Values that are flat, shared across blocks, and don't need their own identity.

Resources

Named, schema-typed containers attached to a scope. Each carries its own state and optionally content:

session: {
  resources: {
    plan: {
      stateSchema: z.object({
        steps: z.array(z.string()).default([]),
        status: z.enum(["draft", "active", "complete"]).default("draft"),
      }),
      writable: true,
    },
  },
}

Good for: artifacts, documents, knowledge entries, configuration bundles. Data that has its own identity, structure, and lifecycle. If you'd naturally think of it as a named object rather than a field, it's a resource.

For dynamic collections where the instance count isn't known ahead of time, see Resource Collections.

Decision table

Signal	Scope state	Resource
Simple scalar or enum	Yes
Counter or flag	Yes
Has content + metadata		Yes
Needs its own identity/name		Yes
Complex nested structure		Yes
Dynamic collection (unknown count)		Collection

Shared vs block-private

State schema fields bubble up into the flow's combined state. Every field name is globally shared within a flow. Two blocks declaring { status: z.string() } and { status: z.number() } will conflict at build time.

Resources don't have this problem. Each is accessed by name through the registry, so two resources can each have a status field without collision.

This matters most for block-private scratch data. If a block needs a cache or intermediate results that other blocks shouldn't touch, use a resource:

const search = handler({
  name: "search",
  sessionResources: {
    searchCache: defineResource({
      stateSchema: z.object({
        lastQuery: z.string().default(""),
        results: z.array(z.string()).default([]),
        cachedAt: z.number().default(0),
      }),
      writable: true,
    }),
  },
  execute: async (input, ctx) => {
    const cache = ctx.session.resources.searchCache;
    if (cache.state.lastQuery === input.query && Date.now() - cache.state.cachedAt < 60_000) {
      return { results: cache.state.results };
    }
    const results = await performSearch(input.query);
    await cache.setState({ lastQuery: input.query, results, cachedAt: Date.now() });
    return { results };
  },
});

Quick rules:

• Multiple blocks need it? Scope state with a specific field name
• One block uses it, generic name? Resource (avoids collisions)
• One block, specific name? Either works. Scope state is simpler

Choosing the right scope

Question	Session	User	Project
Belongs to this conversation?	Yes
Survives across conversations?		Yes
Personal to one user?		Yes
Shared across users?			Yes
Temporary working data?	Yes

Client visibility

Scope state is never directly visible to clients. You expose it through scope-level clientData — computed projections that run server-side:

session: {
  clientData: {
    currentMode: (ctx) => ctx.state.mode,
  },
}

Resources have a second option. Instead of (or in addition to) scope-level clientData, you can declare client config directly on the resource. This gives the frontend lazy-loaded access to resource content and metadata through dedicated hooks and endpoints. See Client Access for the full API.

Choose state vs resources based on the data's nature and lifecycle, not on client visibility.