Follow Up Boss API: Real-Time Integration Explained

What does the Follow Up Boss API actually do?

Follow Up Boss (FUB) exposes a RESTful HTTP API that lets any authorized application read from and write to the CRM's core data objects: people (contacts), deals, tasks, notes, events, stages, and custom fields. Authentication uses API keys scoped to an account, and responses are standard JSON payloads.

The API is the backbone of the FUB integration ecosystem. Lead sources push new contacts in; dialer apps pull call logs; transaction management platforms sync deal stages back. Every integration you see in the FUB marketplace is built on this same API surface.

Beyond CRUD operations, the API supports webhooks — outbound HTTP calls that FUB makes to a URL you register. Webhooks flip the data-flow direction: instead of your app asking FUB "has anything changed?", FUB tells your app the moment something happens. That distinction is what separates near-real-time integrations from integrations that feel stale.

For the authoritative rate limits, payload schemas, and authentication details, see the official documentation at followupboss.com/api-docs. This article focuses on the architectural patterns and what they enable in practice.

How do Follow Up Boss webhooks work for real-time events?

When you register a webhook endpoint with Follow Up Boss, you provide a destination URL and select the event types you want to receive. FUB then sends an HTTP POST to that URL containing a JSON body that describes the event — what changed, on which object, and when.

The receiving server must respond with a 2xx status code to acknowledge receipt. If your server is unavailable or returns an error, FUB will typically retry delivery according to its retry policy. This delivery guarantee means integrations need to be idempotent — processing the same event twice should produce the same result as processing it once.

A typical webhook payload for a new inbound lead includes the person's contact details, the source (Zillow, Realtor.com, a website form, etc.), the timestamp, and any notes captured at lead-in time. An AI layer receiving that payload can immediately begin scoring the lead, checking response time targets, or routing the assignment — all within the same second the lead appears in FUB.

Polling vs. webhooks: what's the difference for FUB data?

Most early FUB integrations used REST polling: call the API every N minutes, compare results against a local snapshot, and act on the diff. Webhooks eliminate that loop. Here's how the two approaches compare:

In practice, sophisticated integrations use both. Webhooks handle real-time event reaction; the REST API handles bulk reads, historical lookups, and write-back operations where the integration needs to confirm the write succeeded before moving on.

What types of events can the FUB API deliver in real time?

FUB's webhook system covers the major lifecycle moments in a real estate CRM. The categories most relevant to AI integrations include:

• Person events — contact created, updated, tagged, stage changed, assigned to a different agent
• Inbound lead events — new lead ingested from a portal, IDX site, or direct form submission
• Communication events — email sent or received, text sent or received, call logged
• Task events — task created, completed, or overdue
• Deal / pipeline events — deal created, stage changed, closed
• Note events — note added to a contact record
• Activity events — property viewed on the agent's IDX site, search saved

Each event type carries enough context in its payload that a downstream system can act without a follow-up API call in most cases — though many integrations do make a single GET request immediately after receiving a webhook to pull the full updated record when they need data fields not included in the event payload.

How do AI integrations use the Follow Up Boss API?

AI layers built on top of FUB typically follow a three-step pattern: listen, analyze, write back.

Listen — The integration registers webhook subscriptions for the events it cares about. When FUB fires a webhook (say, a new Zillow lead just arrived), the AI service receives the payload within seconds.

Analyze — The AI layer runs its logic: scoring the contact's engagement pattern, measuring response time against benchmarks, identifying the preferred communication channel from prior interaction history, or flagging a compliance issue in an outgoing message draft.

Write back — The AI layer uses the FUB REST API to update custom fields on the contact record. Those updated fields are immediately visible to the agent inside FUB — no page refresh needed, no manual data entry.

Follow Up Ace takes this pattern furthest with its agentic layer: 215 MCP tools that let AI models perform actions across the entire FUB surface area — from reading pipeline health to sending follow-up messages to querying property data — all through structured tool calls rather than direct API programming. The MCP connector is available at https://followupace.com/mcp for Claude and at https://followupace.com/api/mcp/sse/ for ChatGPT SSE. See the Agentic page for connection instructions.

What custom fields can you write back to Follow Up Boss via API?

The FUB API lets you create and update custom person fields — key-value pairs that appear on the contact record alongside the built-in fields. Any authorized integration can write to these fields using the PATCH /people/{id} endpoint with a customFields object in the body.

Follow Up Ace uses this mechanism to maintain a set of AI intelligence fields on every contact in your FUB account. These fields are updated in real time via webhook-driven processing — no manual scoring, no scheduled batch jobs:

• Ace Score (0–100) — a composite engagement score calculated from recency, frequency, and channel responsiveness
• Ace Tier — a categorical label (Hot / Warm / Cool / Cold / Dormant) that buckets the contact for quick-glance prioritization
• Ace Status — a text field surfacing the most important next-action context for the contact
• Ace Response Time — how long the team took to respond to this contact's most recent inbound message
• Ace Velocity Score — tracks whether engagement momentum is accelerating or decelerating over the recent window
• Ace Days Since Inbound — the number of days since the contact last initiated contact, useful for identifying contacts going quiet
• Ace Preferred Channel — derived from interaction history: whether this contact responds best to calls, texts, or email

All seven of these fields are available on all Follow Up Ace accounts at no additional cost — they update automatically as FUB webhooks arrive. No configuration required beyond connecting your FUB account.

Teams that want deeper intelligence — seller propensity scoring, pipeline health analysis, revenue forecasting, and the full Ace Trove feature set — can upgrade to an Ace Trove tier starting at $49/month for accounts with up to 5,000 contacts, scaling to $899/month for accounts with up to 500,000 contacts.

Follow Up Boss API integration: step-by-step setup overview

Whether you're building a custom integration or evaluating an existing one, the typical setup sequence looks like this:

1. Generate an API key — In your FUB account settings under "API," create an API key with the appropriate permission scope. Store this key securely; it authenticates every API request your integration makes.
2. Register your webhook endpoint — Provide a publicly reachable HTTPS URL that can accept POST requests. In the FUB developer settings (or via the API itself), register this URL and select the event types you want to receive. FUB will send a verification ping; your endpoint must respond with 200 OK to confirm registration.
3. Handle incoming events — Parse the JSON payload, verify the request is genuinely from FUB (check the signature header if FUB provides one), acknowledge with 200 immediately, then process asynchronously. Responding quickly prevents timeout retries; heavy processing should happen in a background queue.
4. Write back via REST — After your analysis is complete, use PATCH /people/{id} with your computed values to update the contact record. Use the API key from step one as your Bearer token or Basic Auth credential.
5. Test end-to-end — Create a test contact in FUB, trigger an event (add a note, change a stage), confirm your webhook receiver logs the payload, and verify the write-back appears on the contact record in FUB's UI.
6. Monitor and alert — Log every incoming webhook and every outbound API call with timestamps and response codes. Set up alerting for repeated delivery failures, which indicate your endpoint is unreachable or returning errors.

For teams that don't want to maintain custom integration infrastructure, Follow Up Ace handles all of this automatically. Connect your FUB account through the Ace dashboard (one OAuth-style authorization), and the webhook registration, event processing, and field write-back are all managed on your behalf.

What to consider when evaluating any FUB API integration

Not all integrations that claim to work with Follow Up Boss use the API equally well. A few questions worth asking during evaluation:

• Does it use webhooks or polling? Polling integrations will always lag behind real-time event triggers. If response time tracking or live lead alerts matter to your team, confirm webhooks are in use.
• Where does data live? Some integrations copy FUB data to a separate database and serve insights from there. Others read directly from FUB on demand. Understand the data residency implications, especially for brokerage-level compliance requirements.
• What writes does it make to FUB? Any integration writing custom fields or creating notes/tasks is modifying your CRM's primary record of truth. Confirm you understand what will be written, under what conditions, and how to audit or roll back changes.
• Does it respect FUB's rate limits? Aggressive polling or write-back patterns can exhaust your API quota and affect other integrations sharing the same key. Good integrations implement exponential backoff and respect the Retry-After header when rate-limited.
• Is it compliant with Fair Housing rules? AI tools that generate or suggest communications touching on protected class characteristics create liability. Follow Up Ace includes a built-in compliance scanner that checks outgoing message drafts against Fair Housing guidelines before they're sent — see the Compliance page for details.

The Follow Up Boss API is genuinely well-designed for integration work — it's stable, documented, and increasingly powerful as Zillow Group continues investing in the platform. The integrations that get the most value from it are the ones that treat it as a real-time event stream, not a nightly data dump. For a hands-on look at how Follow Up Ace uses it, explore the Guides section or browse the blog for deep dives on specific features.