Connect FieldStacker to anything: your CRM, your website, your own code

Getting your key

1. Start free or sign in to FieldStacker. The API needs a FieldStacker account in good standing.
2. As the business owner, open Settings → API & webhooks.
3. Read and accept the API Terms, then choose Generate API key.
4. Copy the key straight away. It starts with fsk_ and is shown once; FieldStacker keeps only a fingerprint of it. Generating a new key turns the old one off.
5. Put it in your tool or your code as the header Authorization: Bearer fsk_…. Keep it secret, like a password.

The basics

Errors

Every error has the same shape and a matching HTTP status: 400 bad parameter, 401 missing or wrong key, 403 not in your plan or account not active, 404 not found in your account, 409 conflict (for example a time that was just taken), 422 a field is not valid, 429 rate limit, 503 try again shortly.

{"ok": false, "error": {"code": "bad_email", "message": "email is not a valid email address.", "field": "email"}}

Codes you may see on any call: account_inactive (the account is switched off or its plan has ended), terms_not_accepted (accept the API Terms in Settings → API & webhooks), plan_required (that part is not in your plan).

Pagination

Lists answer {"ok": true, "data": [ … ], "next_cursor": "…", "limit": 50}. Pass limit (1–100, default 50) and, for the next page, cursor=<next_cursor> with the same filters. next_cursor is null on the last page.

Idempotency

Send an Idempotency-Key header (any unique string up to 100 characters, a UUID is ideal) on a POST. If the request is retried with the same key and body within 24 hours, you get the first answer back (with Idempotent-Replayed: true) instead of a second customer or booking. The same key with a different body is refused with 422 idempotency_key_reused.

Endpoints

Customers

A customer in FieldStacker is built from their records: quotes, estimates and invoices, completed jobs, card contacts and, for door-knocking trades, won doors. A customer’s id is one of those records, like cus_q1042 (a quote) or cus_c88 (a contact). It is the customer’s oldest record, so it stays the same as new work comes in. Any of the customer’s record_ids finds the same customer, and if two customers are combined in the app, both old ids keep working.

GET v1/customers takes q (name, phone, email or address), updated_since, limit, cursor, newest activity first. POST takes name, phone, email, address, notes (at least a name, phone or email); if those details already match a customer, you get that customer back with "existing": true and nothing new is made. PATCH changes name, business, phone, alt_phone, email, address, notes, tags: what FieldStacker shows for the customer, the same as ✏️ Edit customer in the app. Past quotes and invoices keep what was on them.

curl -s 'https://www.fieldstacker.com/app/api.php?route=v1/customers&q=lopez&limit=20' \
  -H 'Authorization: Bearer fsk_your_key'

curl -s -X POST 'https://www.fieldstacker.com/app/api.php?route=v1/customers' \
  -H 'Authorization: Bearer fsk_your_key' -H 'Content-Type: application/json' \
  -H 'Idempotency-Key: 6f1c2a9e-crm-contact-311' \
  -d '{"name":"Maria Lopez","phone":"775-555-0100","email":"maria@example.com","address":"10 Main St, Reno, NV 89501"}'

Bookings and availability

Bookings come in two types. online_booking (ids like bk_52) is what your booking page makes, and appointment (ids like ap_918) is a job on your schedule. GET v1/bookings takes from, to (default: from 30 days ago), status (pending, confirmed, canceled, declined, completed, no_show, comma-separated), type, in start-time order.

POST v1/bookings books through your booking page’s own rules: the time must be one GET v1/availability offers, your approval setting applies, you get the same notification as a website booking, and your customer gets the same confirmation. Online booking must be switched on in FieldStacker. PATCH moves a booking (start_at), cancels it ("status": "canceled") or confirms a pending one ("status": "confirmed"). Jobs on your schedule that crews work from are changed in FieldStacker; the API can move or cancel only those booked by a customer online.

curl -s 'https://www.fieldstacker.com/app/api.php?route=v1/availability&date=2026-11-03' -H 'Authorization: Bearer fsk_your_key'

curl -s -X POST 'https://www.fieldstacker.com/app/api.php?route=v1/bookings' \
  -H 'Authorization: Bearer fsk_your_key' -H 'Content-Type: application/json' \
  -H 'Idempotency-Key: web-booking-8812' \
  -d '{"start_at":"2026-11-03T10:00:00-08:00","service":"in_home",
       "customer":{"name":"Sam Lee","email":"sam@example.com","phone":"775-555-0142","address":"22 Oak Ave, Sparks, NV"}}'

Estimates and invoices

Read-only. Each has its number, status (estimates: draft, sent, approved; invoices: draft, in_progress, sent, unpaid, paid), the customer, the lines your customer sees, subtotal, tax, total, and for invoices amount_paid, deposit_paid, paid_at. customer_url is the link you already shared with the customer, if there is one. Lists take status, updated_since, most recently changed first.

curl -s 'https://www.fieldstacker.com/app/api.php?route=v1/invoices&status=paid&updated_since=2026-10-01' -H 'Authorization: Bearer fsk_your_key'

Price list and form leads

GET v1/services lists your Equipment & pricing items (q, category) with their customer prices; your costs are never included. GET v1/form-leads lists what visitors sent you, newest first (since, source = website_message, website_form, landing_page or card).

Webhooks

Webhooks send events to your own HTTPS address the moment they happen, so you don’t have to ask. Add up to 5 in Settings → API & webhooks and pick the events for each. Every delivery is a signed JSON POST (X-FieldStacker-Signature: sha256=…, an HMAC of the raw body with that webhook’s secret), retried for about 15 hours if your address does not answer with a 2xx.

GET v1/me always lists the events your account can send, including any added after this page was written.

Good to know

• Each key belongs to one business and sees only that business’s data. The data your team members add to your business is included.
• Only the business owner can make or see a key. Team members and technicians can’t.
• A webhook that creates a lead, sent to a tool that creates a lead in FieldStacker, would loop. Filter on lead_source: "api", or send "notify_webhooks": false when you create leads.
• Questions or a bug? Email support@fieldstacker.com.