Open specification · Apache 2.0 · v1.0

Describe how events flow.
Run exactly that.

FlowDSL is one readable file for nodes, edges and delivery guarantees. Validate it, see it as a graph, run it on any runtime.

Read the spec

Sibling to OpenAPI and AsyncAPI.

Packet:

email-triage.flowdsl.yaml✓ valid

flowdsl: "1.0.0"

info:

title: Email triage

version: "1.0.0"

flows:

email_triage:

entrypoints:

- message: { $ref: "#/components/packets/EmailFetcherPacket" }

nodes:

EmailFetcher:

kind: source

operationId: fetch_inbox

runtime: { language: go }

LLMClassifier:

kind: llm

operationId: classify_intent

runtime: { language: python }

IntentRouter:

kind: router

operationId: route_by_intent

runtime: { language: go }

EmailSender:

kind: terminal

operationId: send_reply

runtime: { language: python }

SlackNotifier:

kind: action

operationId: notify_slack

runtime: { language: typescript }

edges:

- from: EmailFetcher

to: LLMClassifier

delivery: { mode: durable }

- from: LLMClassifier

to: IntentRouter

delivery: { mode: direct }

- from: IntentRouter

when: "output.name == 'routine'"

to: EmailSender

delivery: { mode: checkpoint }

- from: IntentRouter

when: "output.name == 'urgent'"

to: SlackNotifier

delivery: { mode: direct }

components:

packets:

EmailFetcherPacket: { type: object }

routine
urgent

NodeLLM Classifier

Classifies intent and urgency with an LLM; output is a typed packet.

kind: llm
operationId: classify_intent
runtime: Python · gRPC
inputs → outputs: packet → packet

running · Email Fetcher · hop 0/3Interactive preview · click nodes & edges

01
Nodes are business logic
Pure, testable units of work. No transport, no broker code inside.
02
Edges carry the guarantee
Pick a delivery mode per edge — in-process, Redis, Mongo, Postgres or Kafka.
03
The runtime keeps the promise
Retries, checkpoints and replay come from the edge policy, not glue code.

Edge delivery

Five guarantees. One line of YAML.

Choose how much an edge must survive. Same nodes, same code — only the policy changes. Try crashing the consumer.

durable

PRODUCERChargePayment

CONSUMERFulfillOrder

PACKET STOREMongoDB

consumer up · packets delivered

GuaranteeEvery packet persisted until acked

OverheadHigher

Backed byMongo / Postgres

- from: ChargePayment
  to: FulfillOrder
  delivery:
    mode: durable

Use it for: Money, orders and anything that must never be lost.

In production

Change a running app. No redeploy. No downtime.

A published flow version takes effect on the next request — the process keeps serving while you change what it does.

support-bot · production

POST /api/v1/support/chatv12

Publish a new version with a different LLM. The next request uses it.

flows/support-bot.yaml · v12

 nodes:   Answer:     operationId: redelay/llm-chat     kind: llm     settings:       providerID: ollama       model: qwen3-14b       temperature: 0.2

Illustrative numbers. The mechanics are Redelay’s: deployments & A/B variants, trace, debug taps.

Node kinds

Ten kinds of node. Every graph is built from these.

The kind decides a node’s role and how Studio draws it. Pick one to see its card and YAML.

llmLLMClassifier

LLM Classifier

classify_intent

Calls a model and returns a typed result — prompts live in config, not code.

LLMClassifier:
  kind: llm
  operationId: classify_intent

Works with your specs

Completes the API spec family.

Keep your OpenAPI and AsyncAPI documents. FlowDSL references their schemas and adds the part they don’t describe: the flow.

View the JSON Schema

describesOpenAPIHTTP request & responseWhat an endpoint accepts and returns.$ref: "openapi#/components/schemas/Order"

describesAsyncAPIEvents & messagesWhat travels on a channel and its schema.$ref: "asyncapi#/components/messages/OrderPlaced"

addsFlowDSLExecutable flowsHow events move between nodes — and the guarantees.flowdsl: "1.0.0"

Get started

Write it. Validate it.Run it anywhere.

DeclareNodes, edges and delivery in one .flowdsl.yaml.
VisualizeThe canvas is a projection of the file — never the other way round.
ExecuteGo runtime today; Python and TypeScript SDKs in development.

$go run github.com/flowdsl/flowdsl-go/cmd/flowdsl-validate@v0.1.0 my-flow.flowdsl.json

Read the quick start

GoAvailable

Node handlers, spec parser, runtime interfaces

NodeHandler interface, packets and settings
Document parser + structural validator
Runtime interfaces: Engine, Checkpoint, DeliveryAdapter

$go get github.com/flowdsl/flowdsl-go

github.com/flowdsl/flowdsl-go SDK docs

Studio comingThe visual editor for FlowDSL, with two-way YAML sync. Join the waitlist.Join the waitlist

Runtime

Runs on Redelay.See it working.

FlowDSL's Go runtime is Redelay. Publish a flow version and it takes effect on the next request — no restart. Deployments carry stable and canary variants; debug taps watch node I/O without touching it.

Demo adminFlows running in a real Redelay admin
Flow deployments & A/B variantsStable + canary with routing weights
Trace & debug tapsPassive, read-only observers of node I/OTracing ↗Debug taps ↗

redelay.com

Have a project? We'll quote it — free.

The team behind FlowDSL and Redelay builds new AI products — or adds the flow layer to systems you already run.

Ecosystem

Open core.The rest is on its way.

Open sourceSpec, Go SDK, examples, assistant and reference runtime.Available
StudioVisual editor with two-way YAML sync.Coming soon
Node marketplaceShare and install community nodes.Coming soon
CloudRun FlowDSL flows as a managed service.Coming soon

Ask the docs

Answers from the FlowDSL documentation, with links — runs on open models.

Describe how events flow.Run exactly that.

Nodes are business logic

Edges carry the guarantee

The runtime keeps the promise