Agent
The chat-driven builder that picks connectors, drafts workflows and shows you the diff.
Integrations → Agent (/agent), or the What do you want to build? prompt on Home
The agent is the primary way integrations get built in fastn, and there are two ways in: the Agent item in the sidebar, directly under Integrations, or the What do you want to build? prompt on Home. Both land on the same screen, headed Build an integration, which states its own contract:
Describe what you need in plain words. The agents pick the connectors, draft the workflow, and show you the diff before anything runs.
What it drafts is JavaScript — a <slug>.js module exporting export default async function(ctx), opened in the workflow editor for you to read, test and publish.
Sessions
The left rail, headed Sessions, holds your session history. Each session keeps its full conversation, so you can come back to an integration weeks later and continue where you left off rather than re-explaining it. Before you start anything it reads No sessions yet. Click New session to start.
New session starts a fresh build.
Search sessions (⌘K) filters the rail by name.
Collapse sessions sidebar widens the workspace when you are reading a long diff.
Starting from an example
Four cards sit under START FROM AN EXAMPLE, each pairing a goal with the concrete detail that makes it buildable:
Sync deals into billing
Closed-won Salesforce opportunities, custom fields included
Alert before an SLA breaches
Post to Slack when a Zendesk ticket is close to its deadline
Keep a sheet current
Append new HubSpot contacts to a Google Sheet as they arrive
Give an agent scoped access
Read-only Jira for one customer, nothing beyond that
They are written in the shape a good first message takes — a system, a trigger, and the specific thing that moves — and are worth reading before you write your own.
Writing a good first message
The agent handles ambiguity by asking, but you get a better first draft by being specific about four things:
The systems
"HubSpot", "Cin7 Core", not "our CRM"
What starts it
"when a deal is closed-won", "every night at 2am"
What moves
"the company name, the deal amount, and the line items"
The rules
"skip anything under $500", "only the EU warehouse"
The composer carries Attach a file, the message box (Write a message…) and Send.
What it does
The product's own summary is the reliable one: the agents pick the connectors, draft the workflow, and show you the diff before anything runs. In practice that means working out which systems are involved, reusing connectors that already exist and creating the ones that do not, handling authentication in the chat — inline API-key fields, or an OAuth form with client ID, secret and pre-filled scopes — and then writing the workflow code and opening it in the editor.
Generated test cases land on the editor's Test cases tab, grouped as happy-path, pagination, fields, edge-cases and error-handling, each row badged LIVE or MOCK.
The integration plan
Before building, the agent writes an Integration Plan — an actual markdown document (named for the integration, such as plan-hubspot-to-sheets.md) that opens in a side panel. It sets out the trigger, the actions and connectors involved, a field-mapping table with a worked example per row, and a tenancy section. Its header has a download button, so the plan can be reviewed or circulated before anything is created.
Read it. It is the cheapest place to catch a wrong assumption — correcting a mapping here costs a sentence; correcting it after the workflow is generated costs a rebuild.
Build progress
Alongside the plan, a BUILD PROGRESS panel tracks the work as a step count (0/6, 2/6, …) across four phases:
1. Use cases
Plan and confirm the integration with you
2. Connectors
Create and authorise the connectors it needs
3. Workflows
Approve mappings and test cases, build and test the workflow, bind the trigger
4. Embed
Expose the finished integration as a widget
Each phase expands to its named substeps, a completed one collapses to a green check and Complete, and the one in flight shows a spinner against the current substep. Phase counts vary with the integration — a build with no customer-facing surface will not have an Embed phase.
Clarifying questions
Where your brief is ambiguous, the agent asks rather than guesses, rendering the question as selectable answer cards — each with a title and a sentence explaining what choosing it means. Every question also offers Other… for a free-form answer, so you are never limited to the options it drafted. Typical questions cover sync scope (ongoing only, versus an initial backfill first) and tenancy (internal, versus per-customer multi-tenant).
Reading what it did
The agent's tool calls collapse into a single summary line in the chat — Worked · 3 steps, with Show details to expand the individual calls. Documents it produces appear as artifact chips (for example Field Mappings & Connectors) that reopen the full panel.
Two counters are worth watching: the context meter beside the composer (19k / 1000k) shows how much of the session's context window the conversation has consumed, and AI credits in the top bar show what is left of your quota.
Iterating
Follow-up messages refine what exists rather than starting over:
"Add error handling for when the API is down"
"Filter out records without an email address"
"Change the schedule to hourly"
"Notify Slack on failure"
The agent updates code, mappings and test cases together, so they do not drift apart.
Attachments
Attach a file accepts an API spec, a sample payload, a field-mapping spreadsheet. Giving the agent a real payload is the single fastest way to get accurate mappings.
Using the AI assistant is gated by role rather than by an individual permission, so a role that cannot use it cannot be granted access to it one permission at a time.
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