Workflows
Workflow blocks reference
All 15 block types: what each one does, its settings, its exits and what it costs.
Reference2 min readUpdated 23 October 2026
Every block in the palette is executed by the API. Blocks that act on an agent (Agent, Knowledge lookup, Classify, Extract, Guardrail check, MCP tool call) need you to pick one of your agents; they use its model key, knowledge or MCP servers.
Start and End
| Block | What it does |
|---|---|
| Start | Every run starts here, with the inputs you define. Each input is text; required inputs must be filled. Webhook runs may also send extra JSON keys, read as {{input.order.id}}. |
| End | Finishes the run and sets its output. You can have one End per path. |
AI blocks
| Block | What it does | Credits |
|---|---|---|
| Agent | Sends a message to one of your agents and passes its reply on. The agent uses its own model, knowledge and tools, exactly like chat. Times out after 120 s. | 1 per reply |
| Knowledge lookup | Searches an agent's documents, websites, snippets and Q&A and passes the best matches on as text. Results 1 to 10 (default 3) with a minimum score. | Free |
| Classify | Sorts text into one of up to 10 labels you describe, using the agent's model, and continues down that label's exit, or Other. | 1 |
| Extract | Pulls up to 20 fields out of text as JSON. Types: string, number, date, email, boolean. Later blocks read {{steps.<id>.output.<field>}}. | 1 |
| Guardrail check | Checks text against built-in and your own guardrails and continues down Pass or Fail with the reasons. See Guardrails. | 1 only with an AI-judged check |
Tools
| Block | What it does |
|---|---|
| MCP tool call | Calls one tool on one of an agent's MCP servers with arguments you set as JSON, without asking a model. Times out after 30 s. Use Reload servers if a new tool doesn't show. |
| HTTP request | GET, POST, PUT, PATCH or DELETE to a public URL, with headers and a JSON body. The response (up to 512 KB) is passed on; JSON can be read by key. Times out after 20 s. Private addresses are refused and redirects aren't followed. |
Actions
| Block | What it does |
|---|---|
| Send email | Sends an email from SentientOne with your name; replies go to your account email. Up to 5 recipients, 100 emails a day per account, subject up to 200 characters, body up to 50,000. |
| Slack message | Posts to a Slack channel through an incoming webhook URL. Text up to 3,000 characters. The URL is stored encrypted. |
| Webhook | POSTs JSON to your URL, signed with the workflow's whsec_ secret. See Verify webhook signatures. |
A live run that contains any HTTP, Webhook, Slack or Email block costs 1 credit when it starts. Test runs don't.
Logic and data
| Block | What it does |
|---|---|
| Condition | Checks a value and continues down True or False. Operators: contains, does not contain, equals, does not equal, matches regex, is empty, is not empty. |
| Delay | Waits 0 to 30 seconds (default 2), then passes the previous block's output on unchanged. |
| Set value | Builds text or JSON from inputs and earlier outputs, for example to reshape an API response before an email. |
Regular expressions (in Condition and in regex guardrails) run with a 0.25 second timeout and a 300-character pattern limit, so a bad pattern fails its block instead of stalling the run.
Still stuck?
Email us with what you tried and any request id. A person replies.