Getting started with Tracer

Tracer is the layer your authorization or onboarding system calls before a transaction goes through. It runs your fraud, risk, and limit policies in milliseconds and returns ALLOW, DENY, or REVIEW — so the decision lives in one place instead of being scattered across product code. What changes in your operation: decision logic stops living in scattered if statements across services. Rule changes ship through an API the same day, not in the next release. Audit goes from “let me piece together logs from N systems” to “here is the immutable record of why this transaction got this decision.” Trade-off to be honest about: you add one HTTP call to the critical path of every transaction (target p99 under 80ms). In return, you get a single point for policy, audit, and analytics — and you remove duplicated logic from product code.

Who is this guide for? Developers (junior or senior) integrating Tracer for the first time. If you’re evaluating Tracer at a product or strategy level, start with What is Tracer. If you already have it running and need API mechanics, jump to the Tracer API quick start.

This guide walks you through setting up Tracer and running your first validation. In a few steps, you’ll have a working environment ready to validate transactions in real time. For step-by-step API instructions with request and response examples, see the Tracer API quick start.

Why use Tracer

Real-time validation: Make ALLOW/DENY/REVIEW decisions in under 80ms (p99)
Flexible rules: Expression-based rule engine for custom business logic
Spending control: Configure limits by account, portfolio, segment, and period
Complete : Immutable validation records for SOX/GLBA compliance
Product-agnostic: Supports any transaction type (Card, Wire, PIX, Crypto)

By the end of this guide, you will:

Understand Tracer architecture and core concepts
Have a working development environment
Run your first transaction validation
Configure a spending limit

What is Tracer

Tracer is a transaction validation platform that evaluates rules and limits and returns instant decisions. Your system calls Tracer before executing transactions and acts on the decision (ALLOW, DENY, or REVIEW) according to your business logic.

How it works

In this flow:

Rules evaluate expressions against the transaction context
Limits check spending thresholds for applicable scopes
Decision returns ALLOW, DENY, or REVIEW based on evaluation results

Core contexts

Tracer is built around three bounded contexts:

Validation Context - Orchestrates requests, coordinates evaluation, records audit trail
Rules Context - Manages rule definitions and expression evaluation
Limits Context - Manages spending limits and usage tracking

Prerequisites

Before you start, make sure you have:

Docker and Docker Compose installed
Go 1.25.7+ (for local development)
PostgreSQL 16+ (included in Docker Compose)
API Key for authentication

Infrastructure dependencies

Tracer requires the following components:

Component	Version	Purpose
PostgreSQL	16+	Data persistence and audit trail

Ports

Default ports used by Tracer services:

Service	Port	Description
Tracer API	4020	Main REST API
PostgreSQL	5432	Database

Step 1: Set up the environment

You can run Tracer with Docker Compose or locally for development.

Option A: Docker Compose (recommended)

This is the fastest way to start. PostgreSQL starts automatically with the service.

Clone the repository and start the services:

# Clone the repository
git clone https://github.com/lerianstudio/tracer.git
cd tracer

# Setup environment
cp .env.example .env

# Start all services
make up

Option B: Local run

For development, you can run Tracer locally:

# Set environment variables
export DB_HOST="localhost"
export DB_NAME="tracer"
export API_KEY="your-secure-api-key"
export API_KEY_ENABLED="true"
export SERVER_PORT="4020"
export LOG_LEVEL="INFO"

# Start the service
go run cmd/app/main.go

Essential environment variables

Variable	Description	Example
`DB_HOST`	PostgreSQL host	`localhost`
`DB_NAME`	PostgreSQL database name	`tracer`
`API_KEY`	API Key for authentication	`your-secure-api-key`
`API_KEY_ENABLED`	Enable API Key authentication	`true`, `false`
`SERVER_PORT`	API port	`4020`
`LOG_LEVEL`	Log level	`INFO`, `DEBUG`, `ERROR`

Step 2: Authenticate to the API

Tracer supports two authentication modes. Which one you use depends on the deployment topology:

Deployment	Auth header	When to use
Single-tenant	`X-API-Key: <api-key>`	Local development, single-customer BYOC, or any deployment with `MULTI_TENANT_ENABLED=false` (the default).
Multi-tenant (SaaS / BYOC Multi-Tenant)	`Authorization: Bearer <jwt>`	Any deployment with `MULTI_TENANT_ENABLED=true`. The JWT is issued by Access Manager and carries the `tenantId` claim.

The remaining steps in this guide use the single-tenant API Key form because most local-development setups run that way. If your environment is multi-tenant, replace X-API-Key: your-secure-api-key with Authorization: Bearer $JWT in every example.

API Key (single-tenant)

Include the API Key in the X-API-Key header:

GET /v1/rules
X-API-Key: your-secure-api-key

Bearer JWT (multi-tenant)

Include the JWT issued by Access Manager in the Authorization header:

GET /v1/rules
Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...

Tracer extracts the tenantId claim from the JWT and routes the request to the correct tenant database. You never pass the tenant identifier in a header, path, body, or rule scope — the token is the only source of truth.

cURL example

# Single-tenant: List rules
curl -H "X-API-Key: your-secure-api-key" \
  http://localhost:4020/v1/rules

# Multi-tenant: List rules
curl -H "Authorization: Bearer $JWT" \
  https://tracer.lerian.io/v1/rules

API Keys and JWTs should be kept secure. Never expose them in client-side code or public repositories.

API key authentication is disabled by default (API_KEY_ENABLED=false). The provided .env.example keeps it off so local development works without setup, but a production deployment must set API_KEY_ENABLED=true (single-tenant) or MULTI_TENANT_ENABLED=true and PLUGIN_AUTH_ENABLED=true (multi-tenant) before exposing the service.

Step 3: Configure a spending limit

Spending limits control transaction amounts by scope and period. Create a limit using POST /v1/limits.

Limit types

Type	Description	Reset behavior
`DAILY`	Maximum amount per day	Resets at midnight UTC
`WEEKLY`	Maximum amount per week	Resets every Monday at midnight UTC
`MONTHLY`	Maximum amount per month	Resets on 1st of month
`CUSTOM`	Maximum amount for a custom date range	Resets at end of custom period
`PER_TRANSACTION`	Maximum per single transaction	No tracking needed

For detailed configuration of all limit types including time windows and custom periods, see the Spending limits guide.

Scopes

Apply limits to specific contexts:

Segment: Apply to all accounts in a segment (e.g., corporate customers)
Portfolio: Apply to accounts in a portfolio
Account: Apply to a specific account
Transaction type: Apply only to CARD, WIRE, PIX, or CRYPTO

Create a limit

curl -X POST http://localhost:4020/v1/limits \
  -H "X-API-Key: your-secure-api-key" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "Daily Corporate Card Limit",
    "description": "Daily spending limit for corporate card transactions",
    "limitType": "DAILY",
    "maxAmount": "50000.00",
    "currency": "BRL",
    "scopes": [
      {
        "segmentId": "550e8400-e29b-41d4-a716-446655440000",
        "transactionType": "CARD"
      }
    ]
  }'

Activate a limit

curl -X POST http://localhost:4020/v1/limits/{id}/activate \
  -H "X-API-Key: your-secure-api-key"

Limit lifecycle

Limits are created in DRAFT status and follow the lifecycle DRAFT → ACTIVE → INACTIVE. Inactive limits can return to DRAFT for editing or be permanently deleted. Activate a limit to start enforcement. For the full lifecycle and transition rules, see the Spending limits guide.

Monitor usage

Query GET /v1/limits/{id}/usage to check current consumption. The nearLimit flag turns true when utilization is strictly greater than 80% (utilizationPercent > 80), giving operators a heads-up before a limit is exceeded. For detailed configuration options, see the Spending limits guide.

Step 4: Validate your first transaction

With limits configured, you’re ready to validate a transaction using POST /v1/validations.

Submit a transaction for validation

Send a validation request with the transaction context including:

Transaction details (type, amount, currency, timestamp)
Account information
Optional: segment, portfolio, merchant, and custom

curl -X POST http://localhost:4020/v1/validations \
  -H "X-API-Key: your-secure-api-key" \
  -H "Content-Type: application/json" \
  -d '{
    "requestId": "550e8400-e29b-41d4-a716-446655440104",
    "transactionType": "CARD",
    "subType": "credit",
    "amount": "1500.00",
    "currency": "BRL",
    "transactionTimestamp": "2026-02-20T12:00:00Z",
    "account": {
      "id": "550e8400-e29b-41d4-a716-446655440100"
    },
    "merchant": {
      "id": "550e8400-e29b-41d4-a716-446655440103",
      "category": "5411",
      "name": "Test Merchant"
    },
    "metadata": {
      "channel": "mobile"
    }
  }'

The transactionTimestamp must be recent: future timestamps are rejected with TRC-0226 (1-minute clock skew tolerance), and timestamps older than 24 hours are rejected with TRC-0228.

Tracer evaluates all active rules and limits, then returns one of three decisions:

Decision	Meaning	Your system should
`ALLOW`	Transaction approved	Proceed with the transaction
`DENY`	Transaction denied (rule matched or limit exceeded)	Block the transaction
`REVIEW`	Requires manual review	Queue for human review

The response includes details about which rules were evaluated, which matched, and the current limit usage — useful for debugging and customer support.

Why Tracer returns a decision instead of blocking directly. Tracer is a decisioning layer, not an authorization gateway. The calling system is the one that holds the customer relationship, knows the channel, and decides what to do with a DENY — for example, your card-issuing system may decide to honor a DENY for a stand-in pre-auth but still want to capture the request for analytics. By returning a decision, Tracer fits into any authorization flow without owning the customer-facing UX.

For complete payload structure and field details, see the API reference.

Step 5: Create a validation rule

Rules let you define custom business logic that evaluates during validation. Create a rule using the POST /v1/rules endpoint with an expression, action, and optional scopes. For example, to block high-value transactions:

curl -X POST http://localhost:4020/v1/rules \
  -H "X-API-Key: your-secure-api-key" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "Block high-value card transactions",
    "description": "Deny card transactions above R$ 10,000",
    "expression": "amount > 10000",
    "action": "DENY",
    "scopes": [
      {
        "transactionType": "CARD"
      }
    ]
  }'

Activate a rule

curl -X POST http://localhost:4020/v1/rules/{id}/activate \
  -H "X-API-Key: your-secure-api-key"

Active rules are served from an in-memory cache that refreshes every RULE_SYNC_POLL_INTERVAL_SECONDS (default 10). Newly activated rules can take up to ~10 seconds to start being evaluated, and deactivations take effect on the next sync. Plan integration tests accordingly.

Rule lifecycle

Rules follow the same lifecycle as limits: DRAFT → ACTIVE → INACTIVE. To start evaluation, activate the rule using POST /v1/rules/{id}/activate. Active rules can be deactivated and reactivated as needed. For detailed information about rule expressions and lifecycle management, see the Rules engine guide.

Observability

Tracer exposes endpoints for monitoring and observability.

Key metrics

Tracer exposes OpenTelemetry-compatible metrics via the OTLP exporter, plus custom application metrics:

tracer_auth_failures_total{reason} - Authentication failures by reason (missing_api_key, invalid_api_key)
tracer_audit_persist_failures_total - Audit record persistence failures (compliance risk)
tracer_validation_rollback_failures_total - Usage rollback failures during REVIEW decisions (eventual consistency gaps that self-correct at period boundaries)

Standard HTTP request metrics are provided automatically by the OpenTelemetry Fiber middleware.

Verification

Confirm that everything is working correctly.

Checklist

Docker services started and healthy
API Key authentication working
Spending limit configured
Test transaction validated successfully
Rule created and activated

Next steps

You’ve successfully set up Tracer and validated your first transaction. From here, you can explore more advanced features:

Integration guide - Learn how to integrate your authorization system with Tracer
Rules engine - Write validation rules in CEL and manage their lifecycle
Spending limits - Configure and manage spending limits by scope and period
Audit and compliance - Query validation history and understand the audit trail

Quick reference

The three flows you’ll use most:

Validate a transaction: POST /v1/validations — see the Tracer API quick start for the request shape.
Manage rules: /v1/rules (CRUD + lifecycle endpoints /activate, /deactivate, /draft) — see the Rules engine guide.
Manage limits: /v1/limits (CRUD + lifecycle + /usage) — see the Spending limits guide.

For the full endpoint catalog, request/response schemas, and error codes, see the API reference.

What your system should do with each decision

Decision	Tracer recommends	Your system should
`ALLOW`	Approval	Proceed with the transaction
`DENY`	Denial	Block the transaction and inform the user
`REVIEW`	Review	Queue for manual review in your system

Tracer returns decisions as recommendations. Your system is responsible for implementing the appropriate action based on each decision.

Documentation Index

​Why use Tracer

​What is Tracer

​How it works

​Core contexts

​Prerequisites

​Infrastructure dependencies

​Ports

​Step 1: Set up the environment

​Option A: Docker Compose (recommended)

​Option B: Local run

​Essential environment variables

​Step 2: Authenticate to the API

​API Key (single-tenant)

​Bearer JWT (multi-tenant)

​cURL example

​Step 3: Configure a spending limit

​Limit types

​Scopes

​Create a limit

​Activate a limit

​Limit lifecycle

​Monitor usage

​Step 4: Validate your first transaction

​Submit a transaction for validation

​Step 5: Create a validation rule

​Activate a rule

​Rule lifecycle

​Observability

​Key metrics

​Verification

​Checklist

​Next steps

​Quick reference

​What your system should do with each decision

Why use Tracer

What is Tracer

How it works

Core contexts

Prerequisites

Infrastructure dependencies

Ports

Step 1: Set up the environment

Option A: Docker Compose (recommended)

Option B: Local run

Essential environment variables

Step 2: Authenticate to the API

API Key (single-tenant)

Bearer JWT (multi-tenant)

cURL example

Step 3: Configure a spending limit

Limit types

Scopes

Create a limit

Activate a limit

Limit lifecycle

Monitor usage

Step 4: Validate your first transaction

Submit a transaction for validation

Step 5: Create a validation rule

Activate a rule

Rule lifecycle

Observability

Key metrics

Verification

Checklist

Next steps

Quick reference

What your system should do with each decision