Book field jobs by phone with Retell

By the end of this guide your Retell agent will answer a call, find the caller in Crisphive, and book and confirm a technician visit before hanging up.

If a label on your screen differs from this guide, follow the meaning of the step and tell us at support@crisphive.com.

No code is needed. Retell handles the voice (listening, the AI model, speaking). Crisphive handles the scheduling: customers, technicians, skills, working hours and service areas. You connect them by giving Retell one web address and one key, under the agent’s MCPs.

Three words you will meet

What the agent can do

/mcp/voice gives the agent exactly the tools it needs on a phone call, which keeps each turn fast. In Retell you pick the three tools the prompt uses (Step 4); the others are there if you write your own flow.

Before you start

• A Crisphive account where you are the Owner, or have Developer access (needed to create API keys; by default only the Owner has it).
• A Retell account (sign in at dashboard.retellai.com; Google sign-in works). A new account starts on a free trial, and the typed test in Step 6 works without a card. Calls are billed by Retell, so check its pricing for your plan.
• A computer with a modern browser. A microphone is only needed if you also test by voice; a phone number only to go live.
• A default duration on every job type the agent may book (Crisphive: Settings → Job Types). The default type “General” already has one.
• About 30 minutes.

Retell facts that shape the setup

• Header authentication only. Retell has no OAuth sign-in for MCP servers, so you type the API key into a header — including the word Bearer, which Retell does not add for you.
• No automatic retries. If a tool call fails, Retell does not try again; the prompt tells the agent to apologise and say the team will call back. Give Crisphive time with a 20-second timeout.
• Tools are added one at a time. Each Crisphive tool is added with its own Add Tool dialog.
• Tool answers are capped at 15,000 characters. Crisphive’s voice answers fit: the largest measured, getJobRequest, is about 6,500 characters (a job with a crew of several technicians is larger).
• Retell reads the tool list with POST requests. If your IT team watches the logs, a 405 on a GET request is normal: Crisphive does not offer SSE.

Step 1 — Create the Crisphive API key

The key tells Crisphive which business the agent works for and what it may do. You create a test key now and a live key when you go live (see Go live).

Step 2 — Create the agent

Step 3 — Write the agent’s instructions

The agent page shows the agent’s name, a version (V0) and the buttons Test, Conductor and Publish at the top. Below them a row holds the model, the voice and the language; then a large prompt box and the Welcome Message. The right column holds Functions, Knowledge Base & Memory, Speech settings and further down MCPs; the test panel (Test Audio / Test LLM) is on the far right. Changes save automatically (“Auto saved at …”), but callers only get them after you publish.

Thanks for calling [Business name]. I can book a service visit for you. Can I start with the phone number you're calling from?

Step 4 — Connect the agent to Crisphive

On the crisphive MCP card click Add Tools. In the Add Tool dialog, Tool Access Scope lists the ten Crisphive voice tools and takes one at a time, so open the dialog three times — once per tool below. Do not add the others, such as confirmJobRequest: the prompt does not use them.

The values to copy:

MCP name:           crisphive
URL:                https://api.crisphive.com/mcp/voice
Timeout (ms):       20000
Headers:
  Authorization     Bearer chsk_test_…     (chsk_live_… when you go live)
Query Parameters:   (none)

Tools (Add Tools, one at a time — Talk While Waiting → Static Sentence):
  listCustomers                  “One moment while I look that up.”
  listJobRequestBookingWindows   “One moment while I check the schedule.”
  bookAndConfirmJobRequest       “One moment while I book that for you.”

Step 5 — Publish

Step 6 — Test it

In the test panel on the right of the agent page, open Test LLM and choose Manual Chat (“Manually chat with the agent”). It worked on a free trial without a card; Retell shows its price per message on the card. The agent sends the greeting; you type the caller’s side. Use a made-up number in the 555 range of a real area code and an address inside one of your Crisphive service areas. 613-555-01xx numbers are reserved for fiction, and Crisphive never sends texts or emails to 555 numbers or to example.com addresses.

This is what our test chat looked like (the number belonged to a customer already in our Rehearsal data):

To hear the agent, open Test Audio instead, click Run Test and allow the browser to use your microphone. Run a spoken test before going live: a voice call behaves differently from a typed one (numbers and names are heard, not read).

More calls worth trying before you go live:

Check the result

Each Crisphive step shows in the chat as Tool called : name and Tool response : name, with a Debug link on every turn — the place to look when something goes wrong.

Success: the agent reads back the date, time and address, and only then says you are booked. In the Crisphive dashboard (still in Rehearsal), Bookings shows the new job (REQ-CA-…) with status Confirmed, the customer, the address, the day and time, and an assigned technician.

Fallback: custom functions (only if MCPs are unavailable)

MCPs is the way to connect Retell to Crisphive, and it works — we connected it on production. Use custom functions only if your agent has no MCPs section. Only three of the voice tools can be custom functions: createCustomer, createJobRequest and bookAndConfirmJobRequest. Retell never lets the AI fill in a query parameter or a part of the URL, so the tools that need one (listCustomers, listJobTypes, listJobRequestBookingWindows, listMatchingSlots, getJobRequest, and quoteJobRequest and confirmJobRequest, which need the job’s id in the URL) are not possible. The agent can still book, but cannot recognise returning callers or offer open times.

A minimal bookAndConfirmJobRequest function (POST, the Crisphive API, your key in the header):

{
  "name": "bookAndConfirmJobRequest",
  "description": "Book, schedule and confirm a job in one call at scheduled_at (the business's local time, no offset). Returns confirmed true/false.",
  "http": {
    "method": "POST",
    "url": "https://api.crisphive.com/v1/job-requests/book-and-confirm",
    "headers": {
      "Authorization": "Bearer chsk_test_…"
    }
  },
  "parameters": {
    "type": "object",
    "properties": {
      "customer": {
        "type": "object",
        "properties": {
          "full_name": { "type": "string" },
          "phone": { "type": "string", "description": "E.164, e.g. +16135550177" },
          "email": { "type": "string" },
          "sms_opt_in": { "type": "boolean" }
        }
      },
      "address": {
        "type": "object",
        "properties": {
          "line": { "type": "string" },
          "city": { "type": "string" },
          "state": { "type": "string" },
          "postal_code": { "type": "string" },
          "country": { "type": "string" }
        }
      },
      "scheduled_at": { "type": "string", "description": "e.g. 2026-10-06T10:00:00" },
      "description": { "type": "string" },
      "job_type_id": { "type": "string" }
    }
  }
}

If you go this way, remove the listCustomers lookup from step 1 of the prompt (keep the read-back) and the listJobRequestBookingWindows call from step 5, and have the agent ask for a preferred time directly. A time nobody can take comes back as confirmed: false and the job waits in your queue.

Troubleshooting

Go live

Connect a phone number

Until now you talked to the agent in the browser. It answers real calls only once a phone number is attached to it. There are three ways:

Numbers and call minutes are paid to Retell or your phone provider, not to Crisphive. Then call the number from your own phone and book a test visit.

Calls that are not bookings

Not every caller wants a new visit. The prompt already tells the agent what to do with the other calls:

A message is the caller’s name, phone number (read back) and what they need in one sentence. Two setups make sure these calls reach your team.

Setup 1 — Transfer the call to a person.

Setup 2 — Get every message to your team.

What it costs

• Crisphive: jobs booked by the agent count toward your Crisphive plan like any other job. The connection itself needs no add-on.
• Retell: calls are billed by Retell, so check its pricing for your plan. A new account starts on a free trial; the typed Manual Chat test worked on it without a card, and Retell shows its price per message on the card.
• Phone line: numbers and call minutes are paid to Retell or your phone provider, not to Crisphive.

Related guides and reference

• Voice agents overview — the voice tool set and booking rules
• ElevenLabs — a phone agent that books confirmed visits
• Vapi — a phone assistant with the Crisphive MCP tool
• MCP server reference — every tool, the tool profiles and client setup
• Book and confirm a job — the API call behind every booking step