Components

A workflow is built from annotated classes, one per file, in folders by kind — Angular style. Decorators carry metadata; behaviour is a contract the class implements (like implements OnInit); dependencies come through the constructor. The compiler checks every link. Decision: ADR-0009. Every block on this page compiles against the current package.

examples/job-scout/src/
  job-scout.workflow.ts            @Workflow — the module (the paths, defaults, providers, maxSteps)
  workflow-starts/  routers/  agents/  actions/  workflow-finishes/
  tools/  services/  mcp/  rag/  helpers/  environments/

The example examples/job-scout uses every kind below — see Example.

Component rules

Every component reads the same way, top to bottom:

The decorator holds metadata (name, description, input / output DTOs, deps). A flow node's name is kebab-case and ends with its kind — support-agent, main-router, charge-action, chat-workflow-start, chat-workflow-finish, shop-workflow ([name.kind-suffix]) — explicit, never derived from the class, and unique in the application: it keys records, checkpoints, traces, golden sets and the generated types.
The constructor holds the dependencies — private readonly parameters, each named after its type (ordersService: OrdersService); the execution comes the same way (deps: [ExecutionContext], below).
The methods implement a contract:
- your own implementation → implements the contract (ToolHandler<In, Out> for @Tool / @McpTool, ActionHandler<Self> for @Action, RouterHandler<Self> for a code @Router (decidedBy: DecidedBy.Code, Routers), FinishHandler<Self> for a @WorkflowFinish with input, RagConnector for @Rag, JudgeHandler<TReply> for @Judge);
- extending a standard implementation → extends it (SqliteFtsConnector, McpServerClient) and mark overridden methods override (noImplicitOverride is on).
Data is a DTO: a class with one field decorator per field (agboss/dto), so the class is both the type and the runtime check. See DTOs.
Input/output lives in services (@Injectable, *.service.ts: HTTP, files, model calls); helpers are pure (*.helper.ts: parsing, filters, scores).

File conventions

One component per file, the kind in the name; agboss create / agboss generate follow them:

File	Holds
`<name>.workflow.ts`	the `@Workflow` module
`workflow-starts/<name>.workflow-start.ts`	a `@WorkflowStart` — where a run starts (Workflow)
`routers/<name>.router.ts`	a `@Router` with its routes (Routers)
`actions/<name>.action.ts`	an `@Action` — code without a model
`arbiters/<name>.arbiter.ts`	an `@Arbiter` — whether an answer counts for a quorum (Parallel)
`agents/<name>-agent.options.ts`	an options const two agents share (`satisfies Omit<AgentOptions, …>`)
`workflow-finishes/<name>.workflow-finish.ts`	a `@WorkflowFinish` — where a run finishes
`agents/<name>.agent.ts` + `<name>.prompt.md`	an `@Agent`; its prompt file in `promptUrls: ["./<name>.prompt.md"]`
`tools/<name>.tool.ts` + `<name>.tool.test.ts`	a `@Tool` and its test
`tools/<name>.dto.ts`, `mcp/<name>.dto.ts`	the DTOs of the tools / server next to it (plain data classes)
`mcp/<name>.server.ts`	an `@McpServer` and the server tools it uses (`extends McpServerClient`)
`mcp/<name>.mcp.ts`	an `@McpTool` — a tool with its server injected
`rag/<name>.rag.ts`	a `@Rag` knowledge base
`services/<name>.service.ts`	an `@Injectable` (like an Angular service)
`helpers/<name>.helper.ts`	plain functions
`environments/<name>.environment.ts`	an environment's values (Environments)

Prompts are prompt (inline) or promptUrls (files next to the component, read relative to the declaring module), plus promptVariables; {{variables}} are checked at assembly ([prompt.unknown-variable]), a missing file fails with [prompt.missing-file]. Prompts are instructions only: what a node reads comes in its input message (Path scope), never as {{input.…}} ([prompt.input-in-instructions]).

A tool

import { OneOf, Text } from "agboss/dto";

export class OrderQuery {
  @Text({ prompt: "the order id, e.g. A-1042" })
  orderId!: string;
}

export class OrderStatus {
  @OneOf({ values: ["placed", "shipped", "delivered"] })
  status!: "placed" | "shipped" | "delivered";

  @Text({ prompt: "expected delivery day, YYYY-MM-DD" })
  eta!: string;
}

import { Injectable } from "agboss";
import type { OrderStatus } from "../tools/search-orders.dto.js";

@Injectable()
export class OrdersService {
  find(orderId: string): Promise<OrderStatus> {
    return Promise.resolve({ status: orderId.startsWith("A") ? "shipped" : "placed", eta: "2026-11-02" });
  }
}

import { ExecutionContext, Tool, type ToolHandler } from "agboss";
import { OrdersService } from "../services/orders.service.js";
import { OrderQuery, OrderStatus } from "./search-orders.dto.js";

@Tool({
  name: "search_orders",
  description: "Find an order's status by its id",
  input: OrderQuery,
  output: OrderStatus,
  deps: [ExecutionContext, OrdersService],
})
export class SearchOrders implements ToolHandler<OrderQuery, OrderStatus> {
  constructor(
    private readonly executionContext: ExecutionContext,
    private readonly ordersService: OrdersService,
  ) {}

  run(query: OrderQuery): Promise<OrderStatus> {
    this.executionContext.signal.throwIfAborted();
    return this.ordersService.find(query.orderId);
  }
}

run is checked against the decorator's DTOs (a mismatch is a compile error); the core validates input and output, applies timeoutMs and returns errors to the model (invalid input: …).
deps lists the constructor's dependencies in order — a missing, extra or reordered entry is a compile error (standard decorators have no parameter-type metadata, so they are listed once).
run gets only its input — there is no ctx parameter (#280); the execution, its step and the call's idempotency key come from the injected ExecutionContext.
Test it on its own with testTool(SearchOrders, { overrides: [override(OrderBook, FakeOrderBook)] }) — its own container, the frame of a tool call, no new (Tools, Testing).

DTOs

Data shapes — tool inputs and outputs, server tools, the inputs and outputs of flow nodes — are classes with one field decorator per field, imported from agboss/dto. A DTO on a path (a node's input / output, .returns(…), caseOf(…)) ends with Dto ([dto.name]) and its class name is unique in the application ([dto.duplicate-name]); on paths they are wrapped as listOf(Dto), oneOf(A, B), optional(Dto) (input only), historyOf(Dto, { limit }) (input only: the current value and its earlier versions, Path scope) and variant(Dto, value) (an action returning one class of its oneOf). zod stays inside the framework. Decision: ADR-0013; ready-made ones: Standard DTOs.

import { Integer, ListOf, OneOf, Text } from "agboss/dto";

export class JobQuery {
  @Text({ prompt: "what the user wants", minLength: 20 })
  profile!: string;

  @ListOf(Text, { prompt: "places or cities", minItems: 1 })
  locations!: string[];

  @Integer({ prompt: "how many jobs", min: 1, max: 50, default: 20 })
  count!: number;

  @OneOf({ values: ["remote", "office"], optional: true })
  mode?: "remote" | "office";
}

Decorator	Field type	Checked at runtime
`@Text({ minLength?, maxLength?, pattern? })`	`string`	length; `pattern` — your own format (say it in `prompt`)
`@Integer({ min?, max? })` / `@Decimal({ min?, max? })`	`number`	whole / finite number, range
`@Flag()`	`boolean`	—
`@Email()`, `@Url()`, `@Uuid()`	`string`	format
`@DateTime()` / `@Duration()`	`string`	ISO 8601; a date-time needs an offset or `Z`
`@DecimalString({ scale? })`	`string`	`"19.99"`, at most `scale` digits after the point
`@CurrencyCode()` / `@CountryCode()`	`string`	ISO 4217 (`USD`) / ISO 3166-1 alpha-2 (`IL`), from lists
`@PhoneNumber()` / `@MediaType()` / `@TimeZone()`	`string`	E.164 / `type/subtype` / IANA zone (or `UTC`)
`@OneOf({ values })`	their union	one of the values
`@ListOf(Dto or Text…, { minItems?, maxItems? })` / `@Nested(Dto)`	`T[]` / `T`	each element / the nested DTO

Every decorator takes prompt (what the model reads — the field's JSON Schema description), optional: true or a default, sensitive: PiiAction.… (#120: a masking action applied to the field on its way into a model and wherever the arguments are shown — Guards → PII policies) and example.

The compiler checks: the decorator fits the field's type (@Text on a number), optional: true ↔ name?: both ways, @OneOf values ≡ the field's union, the element type of @ListOf / @Nested.
At runtime (a DtoValidationError with the field path and the reason): integer vs decimal, formats, lengths, ranges, list sizes, code lists, cross-field rules of the standard DTOs.
At startup: a field without a decorator → dto.undecorated-field; methods, accessors or #private fields → dto.not-plain-data. A DTO is plain data, so object literals fit it.
Field order is the declaration order — the order the model reads and fills the fields in.
Names: a tool's input and output are a pair from one noun — FileRead → FileContent, JobQuery → JobMatches. A tool that takes nothing: input: NoInputDto. A flow DTO ends with Dto (OrderRequestDto, OfferDraftDto).

An agent

import { Agent } from "agboss";
import { Reasoning } from "agboss/models";

@Agent({
  name: "support-agent",
  description: "Answers questions about orders", // what routers read
  promptUrls: ["./support.prompt.md"], // next to this file; or prompt: "…"
  model: "moonshotai/kimi-k2.6",
  reasoning: Reasoning.off(),
  maxTokens: 2000,
  tools: [SearchOrders],
})
export class SupportAgent {}

Without input / output it is a text agent: it reads the message (WorkflowStartTextDto) and answers text. With them it reads its fields from the path's scope and answers through answer tools (Agents):

@Agent({
  name: "editor-agent",
  description: "Rewrites the draft by the review notes",
  promptUrls: ["./editor.prompt.md"],
  model: "moonshotai/kimi-k2.6",
  input: { draft: OfferDraftDto, changes: ChangesRequestedDto }, // read by type from the path
  output: OfferDraftDto, // or oneOf(ADto, BDto), listOf(XDto); what it is about: in the flow
  maxVisits: 2, // the third edit is refused before its model call
})
export class EditorAgent {}

Two stages of the same work are two classes sharing an options const — one class is one node:

// agents/reviewer-agent.options.ts
export const reviewerAgentOptions = {
  promptUrls: ["./reviewer.prompt.md"],
  model: "moonshotai/kimi-k2.6",
  input: { article: ArticleDto },
  output: ReviewDto,
} satisfies Omit<AgentOptions, "name" | "description">;

// agents/final-reviewer.agent.ts
@Agent({ ...reviewerAgentOptions, name: "final-reviewer-agent", description: "Reviews before publishing" })
export class FinalReviewerAgent {}

The options must be a static object (a call or a conditional spread → [agent.dynamic-options]). The other options — temperature, cache, maxToolCalls, historyLimit, historySummaries, judges + maxRetries, rag (RagMode.Tool / RagMode.Context), memoryStrategy, guardrails and PII policies — are on Configuration and the pages of each feature. How the agent runs: Agents.

An action

Code without a model, a node of the flow (.toAction(ChargeAction)):

@Action({
  name: "charge-action",
  description: "Charges the card",
  input: { order: OrderDto },
  output: ReceiptDto,
  deps: [ExecutionContext, PaymentsService],
})
export class ChargeAction implements ActionHandler<ChargeAction> {
  constructor(
    private readonly executionContext: ExecutionContext,
    private readonly paymentsService: PaymentsService,
  ) {}

  async execute(input: InputOf<ChargeAction>): Promise<OutputOf<ChargeAction>> {
    // each field is { value, producer }; the step's key is the charge's idempotency key
    return this.paymentsService.charge(
      input.order.value,
      this.executionContext.step.idempotencyKey,
    );
  }
}

An action gets only its input; the execution comes through deps: [ExecutionContext]. What it throws is the step's failure (ActionFailedError, the original in cause), taken by an .onError(…) right after it (Rollback).

An arbiter

An @Arbiter (#279) decides whether one answer of a parallel launch counts for its quorum; it is attached in the flow with .acceptedBy(X) and never chooses where to go. decidedBy: DecidedBy.Model — model, prompt, one criteria entry per agent of the launch; DecidedBy.Code — one @OnAnswer(Agent) from<Agent>(answer: XDto): boolean method per agent class (the plain answer; the copy or item through deps: [ExecutionContext]). No …Handler interface: @OnAnswer(Agent) types the method itself, so a wrong answer type, return type or an extra parameter does not compile; coverage is [arbiter.unhandled-agent] at assembly. The whole contract is on Parallel.

The execution context

ExecutionContext (#280) is the one context of an execution — the type and the DI token. Any component takes it through its constructor, like every other dependency, and names the parameter executionContext:

import { ExecutionContext, Injectable } from "agboss";

/** A shared service: called from an action or a tool, it reads the step that called it. */
@Injectable({ deps: [ExecutionContext] })
export class AuditService {
  readonly records: AuditRecordDto[] = [];

  constructor(private readonly executionContext: ExecutionContext) {}

  record(): AuditRecordDto {
    const { executionId, step } = this.executionContext;
    const entry = { executionId, key: step.idempotencyKey };
    this.records.push(entry);
    return entry;
  }
}

Data only, read-only: executionId, threadId, ownerId, signal, workflow (WorkflowDescriptor: type, name, version, startedVersion), step (StepDescriptor: component, nodeId, visitNumber, idempotencyKey, callId, itemIndex, copyNumber) and the tree (parent, root, depth, itemIndex — a per-item child's, #263 — executionOf(W)). No container, no I/O, no input, no metadata: domain data come through input, anything that calls out is a service.
Live, not a snapshot: every read gives the current execution and step — one frame per node visit and per tool call — so a service (one instance for the app, like the one above) is safe in parallel branches. A read outside an execution (a constructor at start) or after its step ended (a forgotten promise) throws ExecutionContextUnavailableError (context.unavailable).
Parent and root are objects (parent?.executionId, root.executionId); executionOf(W) finds the nearest execution of @Workflow W in the chain. All three return the project's own subclass type (this). Above it, executionContext.tenant (TenantContext) and executionContext.tenant.application (ApplicationContext) — the levels, and the project's subclasses declared in @Application({ tenantContext, executionContext }) (#261).

Field reference: Context and Authorization.

Conventions

What agboss generate, the examples and these pages follow — a style guide, not checked:

an explicit return type on every method;
implements …Handler where the kind has one (ToolHandler<In, Out>, ActionHandler<Self>, RouterHandler<Self>, FinishHandler<Self>, JudgeHandler<TReply>, ChannelHandler);
@Injectable classes named by role: …Repository (database access), …Service (calls to an external service), …Provider (system things the app runs on);
injected fields named after their type (ordersService: OrdersService); the execution context's parameter is executionContext;
no decision by matching text (text.includes("refund")): a model turns text into a typed DTO, code decides by types and enums.

MCP

A server declares the server tools the workflow uses; an MCP tool is a tool with the server injected (more: Mcp):

import { ListOf, Text } from "agboss/dto";

export class FileRead {
  @Text({ prompt: "path inside the shortlist folder" }) path!: string;
}
export class FileContent {
  @Text({ prompt: "the file's text" }) content!: string;
}
export class FileWrite {
  @Text() path!: string;
  @Text() content!: string;
}
export class FileWritten {
  @Text() content!: string;
}
export class ChosenJobs {
  @ListOf(Text, { prompt: "links of the jobs the user chose", minItems: 1 }) jobs!: string[];
}
export class SavedJobs {
  @ListOf(Text) added!: string[];
}

import { McpServer, McpServerClient } from "agboss/mcp";
import { FileContent, FileRead, FileWrite, FileWritten } from "./shortlist.dto.js";

const tools = {
  read_text_file: { input: FileRead, output: FileContent },
  write_file: { input: FileWrite, output: FileWritten },
};

@McpServer({
  name: "shortlist",
  transport: "stdio",
  command: "npx",
  args: ["-y", "@modelcontextprotocol/server-filesystem", "./shortlist"],
  tools,
})
export class ShortlistServer extends McpServerClient<typeof tools> {}

import { InjectionToken, TerminalUserChannel, type ToolHandler } from "agboss";
import { McpTool } from "agboss/mcp";
import { ChosenJobs, SavedJobs } from "./shortlist.dto.js";
import { ShortlistServer } from "./shortlist.server.js";

export const SHORTLIST = new InjectionToken<string>("SHORTLIST");

@McpTool({
  server: ShortlistServer,
  name: "save_shortlist",
  description: "Save the jobs the user chose to their shortlist",
  channel: TerminalUserChannel, // a write the user approves first
  input: ChosenJobs,
  output: SavedJobs,
  deps: [ShortlistServer, SHORTLIST],
})
export class SaveShortlist implements ToolHandler<ChosenJobs, SavedJobs> {
  constructor(
    private readonly server: ShortlistServer,
    private readonly file: string,
  ) {}

  async run({ jobs }: ChosenJobs): Promise<SavedJobs> {
    const { content } = await this.server.call("read_text_file", { path: this.file }); // typed by `tools`
    const added = jobs.filter((job) => !content.includes(job));
    await this.server.call("write_file", { path: this.file, content: [content, ...added].join("\n") });
    return { added };
  }
}

server.call(name, args) — the name and arguments are checked by the compiler (by the DTOs' fields), validated and parsed by the declared DTOs.
At startup every declared server tool must exist on the server with a compatible input schema, or the app stops naming it.
Test without a process: mcpServerStub(ShortlistServer, { write_file: … }) in a unit test, or mcpOf(ShortlistServer) in a workflow test (Testing).

A knowledge base

@Rag classes in rag/, bound by agents with a required mode — see Knowledge bases.

The module

import { TerminalUserChannel, Workflow, provide, route, start } from "agboss";
import { WorkflowStartTextDto } from "agboss/dto";
import { ShortlistServer } from "./mcp/shortlist.server.js";
import { OrdersService } from "./services/orders.service.js";

@Workflow({
  name: "shop-workflow",
  version: "2.0.0",
  flow: [
    start(ChatWorkflowStart)
      .returns(WorkflowStartTextDto)
      .toRouter(MainRouter)
      .chooseOne(
        route(SupportAgent)
          .toFinish(ChatWorkflowFinish),
        route(ShortlistAgent)
          .toFinish(ChatWorkflowFinish),
      ),
  ],
  defaults: {
    models: { temperature: 0 },
    router: { model: "typesafe/jev-1.13" },
    tools: { maxToolCalls: 8 },
    history: { limit: 5 },
  },
  maxSteps: 6,
  mcp: [ShortlistServer],
  providers: [OrdersService, provide(SHORTLIST, "./shortlist/shortlist.md")],
})
export class Shop {} // money: the application's @Budgets (FinOps → Budgets)

providers registers what components inject: classes (@Injectable({ deps }), created by the container) and values (provide(TOKEN, value) for an InjectionToken<T>; a raw { provide, useValue } does not compile). The core provides ExecutionContext (the current execution, above), JudgeModel (a judge's own model, Judges), ROUTER_FACTORY (router engines for cheap decisions inside components — their spend during a tool call is the tool's) and the context levels — ApplicationContext (with the environment, typed by @Application({ environment })), TenantContext and the declared subclasses (Context and Authorization).
One container per application instance, no scopes (#261): it holds the providers of the @Application and of every workflow it lists, one instance per class (OrdersService listed by two workflows is one instance), every listed class created at start. There is no scope option and no per-execution container.
Infrastructure — CostLedgerRepository, ExecutionRecordRepository, PausedExecutionRepository, BaseCheckpointSaver — is listed only in @Application({ providers }); a class that extends one in a workflow's providers fails with [di.infrastructure-in-workflow] (App → Infrastructure).
Implementation by inheritance: a dependency on a contract (an abstract class) gets the one listed class that is it or extends it — the same instance as asking for that class; none listed → the framework's default implementation of the contract, if it has one; two → [di.ambiguous-implementation] AuditService depends on AuditRepository, and 2 listed classes implement it: ….
No new: the container creates every instance. providers take classes; values go only with an InjectionToken — provide(AuditRepository, new MemoryAuditRepository()) fails with [di.instance-provider]. One token with two different values (in two workflows, or twice in one) fails with [di.conflicting-values] — use different tokens or an environment value.
Assembly (workflowOf / createApp, before the first request): the dependency graph is checked and every instance is created once, dependencies first. A cycle, an unregistered provider (Consumer: "TOKEN" is not registered …), an undecorated class in providers ([di.undecorated-provider]), a channel role with no or two implementations in @Application({ providers }) ([di.missing-implementation], [di.ambiguous-implementation], #267), a missing prompt file or prompt variable fail with the component's name.
Lifecycle hooks: implements OnInit, OnStart, OnStop, OnDestroy, each optional (App → Lifecycle hooks).

Components keep no state

One execution is not tied to one application instance: after a pause another instance may continue it. So a component holds no state of an execution — neither a field set in a method nor a Map<executionId, …>. It reads the execution from the live ExecutionContext; data that must outlive a step live in the graph state (a node's output on the path); caches and deduplication are your own service over external storage:

@Injectable({ deps: [RedisClientProvider] })
export class SeenJobsRepository {
  constructor(private readonly redisClientProvider: RedisClientProvider) {}

  async markSeen(executionId: string, jobId: string): Promise<boolean> {
    const added: number = await this.redisClientProvider.client.sAdd(`seen:${executionId}`, jobId);
    return added === 1;
  }
}

The lint rule agboss/no-component-state flags an assignment to this.x (=, +=, ++) outside the constructor of any component (@Injectable, @Tool, @McpTool, @Rag, @Action, a code @Router, @Judge, @InputGuardrail / @OutputGuardrail, @PiiPolicy, @Channel, @A2AAgent).

agboss describe shows each tool's dependencies.

Add…

a tool — tools/<name>.dto.ts + tools/<name>.tool.ts, listed in an agent's tools; a service it needs goes in providers.
an agent — agents/<name>.agent.ts (+ <name>.prompt.md), one route in its router's routes, and its path in the router's choice (route(NewAgent).toFinish(…)).
an action — actions/<name>.action.ts, a step of a path (.toAction(NewAction)).
an MCP server — @McpServer + @McpTool classes in mcp/, the server in @Workflow({ mcp }).

agboss generate <kind> <name> --workflow <path> (alias agb g) writes and wires each of them, then regenerates .agboss/types.d.ts (CLI).

AGBoss

Components

Components

Component rules

File conventions

A tool

DTOs

An agent

An action

An arbiter

The execution context

Conventions

MCP

A knowledge base

The module

Components keep no state

Add…

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Core Concepts

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