SLTax360 API

Developer Hub

The API does two jobs with one key. Invoice push: your system sends each policy transaction, and we prepare and submit the surplus lines filing. Tax calculator: your system asks for the surplus lines tax and fees on a premium. Start with the part you need.

Send your first invoice

SLTax360 files surplus lines tax for the policies your system writes.

• You send each policy transaction from your system: a new policy, a renewal, an endorsement or a cancellation.
• We prepare and submit the state filing. The licensed broker stays responsible for the filing.
• You start small. Six fields are enough for the first call. Add more data later.

You need an API key. It looks like sltax_t2_ followed by 32 letters and digits. If you do not have one, get a free test key: our team sets up a separate test account for you. Put your key in an environment variable called SLTAX_API_KEY, so it stays out of your code.

curl https://api.sltax360.com/api/v1/auth/me \
  -H "Authorization: Bearer $SLTAX_API_KEY"

A 200 reply with your key name and tier means the key works. A 401 means the key is missing or wrong.

curl -X POST https://api.sltax360.com/api/v1/invoices \
  -H "Authorization: Bearer $SLTAX_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "policy_number": "DEMO-0001",
    "insured_name": "Harbor Point Marine LLC",
    "state_code": "TX",
    "net_premium": 12500.00,
    "effective_date": "2026-10-01",
    "expiration_date": "2027-10-01"
  }'

The reply is 201 Created. Your ids and times will be different:

{
  "success": true,
  "data": {
    "id": 12832,
    "policy_number": "DEMO-0001",
    "invoice_number": null,
    "invoice_date": "2026-10-01",
    "insured_name": "Harbor Point Marine LLC",
    "state": { "id": 45, "code": "TX", "name": "Texas" },
    "type": { "id": 1, "name": "New" },
    "lob": null,
    "net_premium": 12500,
    "commission": null,
    "effective_date": "2026-10-01",
    "expiration_date": "2027-10-01",
    "status": "new",
    "filed": false,
    "paid": false,
    "created": "2026-09-23 11:55:21",
    "company": null,
    "policy_id": 6909,
    "policy_fee": 0,
    "stamps_fee": 0,
    "service_fee": 0,
    "notes": null,
    "fees": [],
    "coverages": [],
    "insurers": [],
    "documents": []
  },
  "meta": {
    "timestamp": "2026-09-23T16:55:21Z",
    "request_id": "req_070f04a750ae11ebefd69589",
    "response_time_ms": 9
  }
}

The integration ladder

Climb only as far as you need. Each step works on its own.

First invoice in your language

Each example sends the same 6-field invoice and prints the new invoice id. They all read your key from SLTAX_API_KEY.

• cURL
• JavaScript
• Python
• PHP
• C#

curl -X POST https://api.sltax360.com/api/v1/invoices \
  -H "Authorization: Bearer $SLTAX_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "policy_number": "DEMO-0001",
    "insured_name": "Harbor Point Marine LLC",
    "state_code": "TX",
    "net_premium": 12500.00,
    "effective_date": "2026-10-01",
    "expiration_date": "2027-10-01"
  }'

const response = await fetch("https://api.sltax360.com/api/v1/invoices", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.SLTAX_API_KEY}`,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    policy_number: "DEMO-0001",
    insured_name: "Harbor Point Marine LLC",
    state_code: "TX",
    net_premium: 12500.00,
    effective_date: "2026-10-01",
    expiration_date: "2027-10-01",
  }),
});

const result = await response.json();
if (response.status === 201) {
  console.log("Created invoice", result.data.id, "status:", result.data.status);
} else {
  console.error(response.status, result.error.message, JSON.stringify(result.error.details));
}

import os
import requests

response = requests.post(
    "https://api.sltax360.com/api/v1/invoices",
    headers={"Authorization": f"Bearer {os.environ['SLTAX_API_KEY']}"},
    json={
        "policy_number": "DEMO-0001",
        "insured_name": "Harbor Point Marine LLC",
        "state_code": "TX",
        "net_premium": 12500.00,
        "effective_date": "2026-10-01",
        "expiration_date": "2027-10-01",
    },
    timeout=30,
)

result = response.json()
if response.status_code == 201:
    print("Created invoice", result["data"]["id"], "status:", result["data"]["status"])
else:
    print(response.status_code, result["error"]["message"], result["error"].get("details"))

<?php
$payload = [
    'policy_number'   => 'DEMO-0001',
    'insured_name'    => 'Harbor Point Marine LLC',
    'state_code'      => 'TX',
    'net_premium'     => 12500.00,
    'effective_date'  => '2026-10-01',
    'expiration_date' => '2027-10-01',
];

$ch = curl_init('https://api.sltax360.com/api/v1/invoices');
curl_setopt_array($ch, [
    CURLOPT_POST           => true,
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_HTTPHEADER     => [
        'Authorization: Bearer ' . getenv('SLTAX_API_KEY'),
        'Content-Type: application/json',
    ],
    CURLOPT_POSTFIELDS     => json_encode($payload),
]);
$body   = curl_exec($ch);
$status = curl_getinfo($ch, CURLINFO_HTTP_CODE);
$result = json_decode($body, true);

if ($status === 201) {
    echo "Created invoice {$result['data']['id']} status: {$result['data']['status']}\n";
} else {
    echo "$status {$result['error']['message']}\n";
    echo json_encode($result['error']['details'] ?? null), "\n";
}

using System;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;
using System.Text.Json;

var client = new HttpClient();
client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(
    "Bearer", Environment.GetEnvironmentVariable("SLTAX_API_KEY"));

var payload = """
{
  "policy_number": "DEMO-0001",
  "insured_name": "Harbor Point Marine LLC",
  "state_code": "TX",
  "net_premium": 12500.00,
  "effective_date": "2026-10-01",
  "expiration_date": "2027-10-01"
}
""";

var response = await client.PostAsync(
    "https://api.sltax360.com/api/v1/invoices",
    new StringContent(payload, Encoding.UTF8, "application/json"));

var body = await response.Content.ReadAsStringAsync();
using var json = JsonDocument.Parse(body);
if ((int)response.StatusCode == 201)
{
    var data = json.RootElement.GetProperty("data");
    Console.WriteLine($"Created invoice {data.GetProperty("id")} status: {data.GetProperty("status")}");
}
else
{
    Console.WriteLine($"{(int)response.StatusCode} {body}");
}

Step 2: send what you have

All of these fields are optional. Send the ones your system has. The more you send, the less our team must ask you.

Endorsements and cancellations

• Send the same policy_number as the original policy, with type_code ENDORSEMENT or CANCELLATION.
• Send the date the change takes effect as effective_date, and the policy's expiration date as expiration_date. The state filing uses effective_date as the date of the change.
• Known limit today: the API has one date pair, so the stored policy record takes these dates, and its start date then shows the date of the change. On accounts with the new features, send the policy term instead, and the date of the change in transaction_effective_date.
• Every amount is the amount of the change, not the policy total: net_premium, coverage amounts, insurer amounts and the tax you billed on the change. Amounts that return premium are negative.
• Use preview to work out the tax on the change. Unlike the calculator, POST /invoices/preview accepts negative amounts and returns negative tax lines for a return of premium.
• On read-back, type.name is New, Renewal, Endorsement or Cancelled.

{
  "policy_number": "DEMO-0002",
  "insured_name": "Harbor Point Marine LLC",
  "state_code": "TX",
  "type_code": "ENDORSEMENT",
  "net_premium": 1200.00,
  "effective_date": "2027-01-15",
  "expiration_date": "2027-10-01",
  "coverages": [
    { "code": "9334", "amount": 1200.00 }
  ],
  "insurers": [
    { "company_id": 167, "percent": 100 }
  ],
  "fees": [
    { "type": "sl_tax", "amount": 58.20 },
    { "type": "stamping_fee", "amount": 0.48 }
  ]
}

A cancellation has the same shape, with "type_code": "CANCELLATION" and negative amounts, for example "net_premium": -6250.00.

{
  "policy_number": "DEMO-0002",
  "insured_name": "Harbor Point Marine LLC",
  "state_code": "TX",
  "type_code": "NEW",
  "net_premium": 12500.00,
  "effective_date": "2026-10-01",
  "expiration_date": "2027-10-01",
  "insured_address": {
    "line1": "100 Harbor Drive",
    "city": "Galveston",
    "zip": "77550"
  },
  "coverages": [
    { "code": "9334", "amount": 12500.00 }
  ],
  "insurers": [
    { "company_id": 167, "percent": 100 }
  ],
  "fees": [
    { "type": "policy_fee_company", "amount": 150.00 }
  ]
}

The company_id above is only an example. Ids belong to your account, so always look them up with GET /companies/search.

Features on new accounts

These features are optional, and we switch them on per account. New integrations can ask for them when they request a key. On an account without them, the API ignores the extra fields and the header, exactly as described above.

curl -X POST https://api.sltax360.com/api/v1/invoices \
  -H "Authorization: Bearer $SLTAX_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: DEMO-0001-new-2026-10-01" \
  -d '{
    "policy_number": "DEMO-0001",
    "insured_name": "Harbor Point Marine LLC",
    "state_code": "TX",
    "net_premium": 12500.00,
    "effective_date": "2026-10-01",
    "expiration_date": "2027-10-01"
  }'

{
  "policy_number": "DEMO-0002",
  "insured_name": "Harbor Point Marine LLC",
  "state_code": "TX",
  "type_code": "ENDORSEMENT",
  "net_premium": 1200.00,
  "effective_date": "2026-10-01",
  "expiration_date": "2027-10-01",
  "transaction_effective_date": "2027-01-15",
  "lob_name": "General Liability",
  "coverages": [
    { "code": "9334", "amount": 1200.00 }
  ],
  "insurers": [
    { "naic": "19437", "percent": 100 }
  ],
  "fees": [
    { "type": "sl_tax", "amount": 58.20 },
    { "type": "stamping_fee", "amount": 0.48 }
  ]
}

"filing": {
  "state_status": "not_sent",
  "updated_at": null,
  "confirmation_number": null,
  "submission_number": null,
  "message": null,
  "api_error": null
}

Common errors and the fix

These are the errors partners really hit, taken from our request log. A 422 reply lists the problems in error.details.fields. Insurer and coverage errors are listed under insurers or coverages, and the message names the item, for example insurers[0].

On POST /invoices/preview, problems with the data itself come back in a 200 reply, inside validation.errors. The most common ones:

What happens after you send

1. The invoice is stored in your SLTax360 account. Our team reviews it and fills any gaps.
2. We prepare and submit the state filing. Direct electronic filing exists in 25+ states. In other states we prepare the filing for the state's own process. The licensed broker stays responsible for the filing.
3. You read the status with GET /api/v1/invoices/{id}:
   • status: new, sent, success, error or re-submitted.
   • filed: true once the status is sent, success or re-submitted.
   • paid: always false today. Do not use it yet.
   • created: server time, US Central, without a time zone in the value.

Words you will see

You do not need to know insurance to connect. These are the terms the API uses.

Surplus lines

Insurance from a company that is not licensed in the state. It is allowed for risks that licensed companies do not cover. The state taxes it, and each policy must be filed with the state.

Admitted insurer

An insurance company that is licensed in the state. Its policies do not need a surplus lines filing.

Premium

The price of the policy. In the API: net_premium.

Endorsement

A change to a policy during its term, for example a new vehicle. It can add premium or return premium (a negative amount). Send it with type_code ENDORSEMENT.

Renewal and cancellation

A renewal is the next term of a policy (RENEWAL). A cancellation ends a policy early and usually returns premium (CANCELLATION).

NAIC code

A 5-digit number that identifies an insurance company in the US. Use it to find our company_id with GET /companies/search.

Stamping fee

A small fee that some states charge on top of the tax. It pays for the state office that checks the filings.

Line of business

The kind of insurance, for example general liability or commercial auto. In the API: lob_id, from GET /lobs.

Coverage code

A short code for one coverage in the policy. States use it to see what was insured. Codes differ by state.

Tools

• Interactive reference: Swagger UI. Click Authorize, paste your key, then use Try it out. Every call there is real.
• OpenAPI 3.0 spec: openapi.json, to generate a client in your language.
• Postman collection: sltax360-api.postman_collection.json. It follows the ladder above. Set api_key before you run it.
• Help: email support@sltax360.com with the request_id from the reply.

Authentication

All API requests require a Bearer token in the Authorization header.

Authorization: Bearer sltax_t2_your_api_key_here

Token Format

A key is sltax_, then the tier (t1, t2 or t3), then 32 lowercase letters and digits. The tier sets what the key can do and its hourly limit (see Rate Limits). Creating invoices needs Standard (t2) or higher. The calculator needs the calculator scope on the key. Your key also decides which SLTax360 account your data goes to.

Get a Free Test Key

Tax Calculator: Quick Start

Calculate surplus lines tax for a $50,000 premium in Texas with a single API call:

curl -X POST https://api.sltax360.com/api/v1/calculator/estimate \
  -H "Authorization: Bearer $SLTAX_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "state": "TX",
    "premium": 50000,
    "policy_fees": 500
  }'

The response includes an itemized breakdown of every tax and fee. Rates change over time; the reply always uses the rates in force on effective_date (today if you leave it out). This reply was captured on 2026-09-23:

{
  "success": true,
  "data": {
    "state": { "id": 45, "code": "TX", "name": "Texas" },
    "input": { "premium": 50000, "policy_fees": 500, "effective_date": "2026-09-23" },
    "tax_base": 50500,
    "line_items": [
      { "name": "Surplus Lines Tax", "code": "sl_tax", "rate": 4.85, "rate_type": "percentage", "amount": 2449.25, "unrounded_amount": 2449.25 },
      { "name": "Stamping Fee", "code": "stamping_fee", "rate": 0.04, "rate_type": "percentage", "amount": 20.2, "unrounded_amount": 20.2 }
    ],
    "rounding_rule": "standard",
    "total_taxes_and_fees": 2469.45,
    "total_due": 52969.45,
    "special_notes": "Texas: 4.85% SL tax, 0.04% stamping fee to SLTX. Tax is on total gross premium including fees.",
    "calculated_at": "2026-09-23T12:01:38-05:00",
    "disclaimer": "Estimate only. Figures are calculated from published state rates and are not a guarantee of the amounts due. Verify with the applicable state or stamping office before filing."
  },
  "meta": {
    "timestamp": "2026-09-23T17:01:38Z",
    "request_id": "req_0daae76f3d9022291759a04f",
    "response_time_ms": 13
  }
}

POST /estimate

Calculate surplus lines taxes and fees for a given state and premium amount. Returns an itemized breakdown of all applicable taxes and fees.

Request Parameters

Send as JSON request body.

Response Fields

Line Item Codes

Not all codes appear for every state. The response only includes line items applicable to the requested state.

Fee / Tax Codes (for fees[] array input)

All codes below are accepted as fees[].type on /api/v1/invoices (preview and create). Policy-level fees feed into the per-state tax base (e.g. Texas taxes Policy + Inspection + Broker; California excludes Inspection). Tax codes at the bottom of the table (sl_tax, stamping_fee, etc.) are accepted so callers can persist the billed amounts verbatim. The create endpoint stores fees[] as you send them; it does not recompute. One exception: in states with a flat stamping fee per policy, we may set that fee ourselves (it is 0 on an endorsement or a cancellation).

Aliases: fire_marshal/fire_marshall_tax, slas_fee/clearinghouse_fee, and flat_fee/filing_fee map to the same stored column. Send only one of each pair per request; mixing both returns 422.

Example with fees array

{
  "state": "TX",
  "premium": 50000,
  "fees": [
    { "type": "policy_fee_company", "amount": 250 },
    { "type": "broker_fee", "amount": 150 },
    { "type": "inspection_fee", "amount": 100 },
    { "type": "filing_fee", "amount": 25 }
  ]
}

For Texas, the tax_base = $50,000 + $250 (policy) + $150 (broker) + $100 (inspection) = $50,500. The $25 filing fee is pass-through (not taxed). The response also includes a fee_breakdown object.

Response Format

All responses use a consistent JSON envelope with success, data/error, and meta fields.

Success Response

{
  "success": true,
  "data": { /* endpoint-specific data */ },
  "meta": {
    "timestamp": "2026-09-23T17:01:38Z",
    "request_id": "req_0daae76f3d9022291759a04f",
    "response_time_ms": 45
  }
}

Error Response

{
  "success": false,
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Validation failed",
    "details": { /* field-level errors when applicable */ }
  },
  "meta": { /* same as success */ }
}

Meta Object

Error Codes

Validation Error Example

{
  "success": false,
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Validation failed",
    "details": {
      "fields": {
        "state": ["Must not exceed 2 characters"],
        "premium": ["Must be at least 0.01"]
      }
    }
  }
}

Rate Limits

Each API key has an hourly limit, set by the key's API tier. The count starts again at the start of each clock hour. Every call counts, including invoice previews.

Response Headers

Limits by API Tier

State-Specific Rules

Each state has unique tax rules that the API handles automatically. Here are the key concepts:

Tax Base Composition

Some states include policy fees in the tax base; others tax only the premium. The API determines this automatically based on the state, so you just provide both values.

Rounding Rules

How many line items to expect

Some states charge only the surplus lines tax. Others add a stamping fee, a fire marshal tax or a flat filing fee, so a reply can have one line item or several. Rates change over time, so do not copy them into your code: read them from the API. Each reply uses the rates in force on the effective_date you send.

Calculator Code Examples

• cURL
• JavaScript
• Python

curl -X POST https://api.sltax360.com/api/v1/calculator/estimate \
  -H "Authorization: Bearer sltax_t2_your_api_key_here" \
  -H "Content-Type: application/json" \
  -d '{
    "state": "FL",
    "premium": 75000,
    "policy_fees": 250,
    "effective_date": "2026-03-01"
  }'

const response = await fetch('https://api.sltax360.com/api/v1/calculator/estimate', {
  method: 'POST',
  headers: {
    'Authorization': 'Bearer sltax_t2_your_api_key_here',
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    state: 'FL',
    premium: 75000,
    policy_fees: 250,
    effective_date: '2026-03-01',
  }),
});

const result = await response.json();

if (result.success) {
  console.log('Total due:', result.data.total_due);
  result.data.line_items.forEach(item =>
    console.log(`  ${item.name}: $${item.amount}`)
  );
} else {
  console.error('Error:', result.error.message);
}

import requests

response = requests.post(
    "https://api.sltax360.com/api/v1/calculator/estimate",
    headers={
        "Authorization": "Bearer sltax_t2_your_api_key_here",
        "Content-Type": "application/json",
    },
    json={
        "state": "FL",
        "premium": 75000,
        "policy_fees": 250,
        "effective_date": "2026-03-01",
    },
)

result = response.json()

if result["success"]:
    data = result["data"]
    print(f"Total due: ${data['total_due']:,.2f}")
    for item in data["line_items"]:
        print(f"  {item['name']}: ${item['amount']:,.2f}")
else:
    print(f"Error: {result['error']['message']}")

Getting Started