OFAC API in C# / .NET: screening and error handling

What this C# / .NET integration does

OFAC is the U.S. Treasury authority that publishes the SDN and non-SDN sanctions data. This tutorial calls SanctionsKit, not an OFAC-operated screening endpoint. Keep the original authority and list identity visible in each result.

The client submits a subject, validates the response, and prints only the screening ID, status, and candidate count. It does not approve a customer, resolve an identity, or make a legal decision. A nonzero exit leaves the local operation incomplete.

Prepare the runtime and a synthetic request

Use .NET 8 or later. Save the program as Program.cs and the project file shown below as Screen.csproj. HttpClient and System.Text.Json are included; no provider SDK or third-party JSON library is required.

Save the following as request.json. Mira Calder is an invented subject and sandbox@1 uses synthetic fixtures, not a current production sanctions search. Set SANCTIONSKIT_API_KEY to your test key in the process environment. Set SCREENING_OPERATION_ID to a new persistent identifier for this operation, and reuse it only for an unchanged retry.

{
  "subject": {
    "name": "Mira Calder",
    "entityType": "person",
    "birthDate": "1984"
  },
  "package": "sandbox@1",
  "retention": "standard"
}

Add the project configuration

Save this as Screen.csproj. These dependencies are for the standalone tutorial, not dependencies to add to SanctionsKit’s website build. Review and lock them under your own maintenance process.

<Project Sdk="Microsoft.NET.Sdk"><PropertyGroup><OutputType>Exe</OutputType><TargetFramework>net8.0</TargetFramework><ImplicitUsings>enable</ImplicitUsings><Nullable>enable</Nullable></PropertyGroup></Project>

Send the request and validate the result

Save the client as Program.cs. The endpoint is fixed to SanctionsKit’s HTTPS API. The example rejects redirects, requires explicit authorization before using a live key, and does not retry automatically. Production integrations should preserve the operation state before the first network call.

// .NET 8+. Backend or trusted CLI. No third-party packages.
using System.Net.Http.Headers;
using System.Text;
using System.Text.Json;
try
{
    var key = Environment.GetEnvironmentVariable("SANCTIONSKIT_API_KEY") ?? "";
    var operation = Environment.GetEnvironmentVariable("SCREENING_OPERATION_ID") ?? "";
    if (key.Length == 0 || operation.Length == 0) throw new InvalidOperationException("Missing configuration");
    if (!key.StartsWith("sk_test_", StringComparison.Ordinal) && !(key.StartsWith("sk_live_", StringComparison.Ordinal)
        && Environment.GetEnvironmentVariable("ALLOW_LIVE_SCREENING") == "yes"))
        throw new InvalidOperationException("Live operation not explicitly authorized");
    var raw = await File.ReadAllBytesAsync(args.Length > 0 ? args[0] : "../request.sandbox.json");
    if (raw.Length > 65536) throw new InvalidDataException("Oversized request");
    using var input = JsonDocument.Parse(raw);
    var body = input.RootElement;
    if (body.ValueKind != JsonValueKind.Object || !body.TryGetProperty("subject", out _) ||
        body.TryGetProperty("sources", out _) == body.TryGetProperty("package", out _))
        throw new InvalidDataException("Invalid request object");
    using var handler = new HttpClientHandler { AllowAutoRedirect = false };
    using var client = new HttpClient(handler) { Timeout = TimeSpan.FromSeconds(25) };
    using var deadline = new CancellationTokenSource(TimeSpan.FromSeconds(30));
    using var request = new HttpRequestMessage(HttpMethod.Post, "https://www.sanctionskit.com/api/v1/screenings");
    request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", key);
    request.Headers.Add("Idempotency-Key", operation);
    request.Content = new StringContent(Encoding.UTF8.GetString(raw), Encoding.UTF8, "application/json");
    using var response = await client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, deadline.Token);
    if (!response.IsSuccessStatusCode) throw new HttpRequestException("Incomplete HTTP response");
    await using var stream = await response.Content.ReadAsStreamAsync(deadline.Token);
    using var received = new MemoryStream();
    var buffer = new byte[8192]; int read;
    while ((read = await stream.ReadAsync(buffer.AsMemory(), deadline.Token)) != 0)
    {
        if (received.Length + read > 8 * 1024 * 1024) throw new InvalidDataException("Oversized response");
        received.Write(buffer, 0, read);
    }
    using var envelope = JsonDocument.Parse(received.ToArray());
    var root = envelope.RootElement;
    if (root.ValueKind != JsonValueKind.Object || !root.TryGetProperty("data", out var data) || data.ValueKind != JsonValueKind.Object ||
        !data.TryGetProperty("id", out var id) || id.ValueKind != JsonValueKind.String || string.IsNullOrEmpty(id.GetString()) ||
        !data.TryGetProperty("status", out var state) || state.ValueKind != JsonValueKind.String ||
        !data.TryGetProperty("matches", out var matches) || matches.ValueKind != JsonValueKind.Array)
        throw new InvalidDataException("Unexpected screening response");
    var status = state.GetString(); var count = matches.GetArrayLength();
    if ((status != "potential_match" && status != "no_match") || (status == "no_match" && count != 0) || (status == "potential_match" && count == 0))
        throw new InvalidDataException("Inconsistent screening response");
    Console.WriteLine(JsonSerializer.Serialize(new { id = id.GetString(), status, candidateCount = count }));
}
catch (Exception)
{
    Console.Error.WriteLine("Screening incomplete. Check the operation before retrying.");
    Environment.ExitCode = 1;
}

Run the client

Run this from the directory containing request.json and the project files. Keep the API key out of committed files and shell tracing. The tutorial’s request-file limit is 64 KiB and its response parsing limit is 8 MiB; these are client safeguards, not claims about API service limits.

Use ResponseHeadersRead with an explicit cancellation token that also covers body reads. Check JsonValueKind before reading a field. In a long-running application, use your established HttpClient lifetime management rather than allocating one client for every customer.

dotnet run --project Screen.csproj -- request.json

Change to the required production coverage

The production example selects ofac-sdn only. Add ofac-non-sdn only when your required scope includes it, after checking current availability and compatibility. An SDN-only check is not a complete non-SDN check, and non-SDN records do not all have the same restrictions.

For an authorized production operation, replace the package field with the sources array shown below, supply the actual lawfully held subject details, use a live key, and set ALLOW_LIVE_SCREENING=yes. Keep the complete request in request.json and create a new operation ID. Do not send both sources and package. The fragment below is a coverage change, not a complete request.

{
  "sources": [
    "ofac-sdn"
  ]
}

Preserve the source details a reviewer needs

Preserve source record IDs, list names, program context, aliases, date precision, and the actual fields that support or conflict with a candidate. A no-match result does not resolve OFAC’s 50 Percent Rule, geography-based restrictions, or the legality of a proposed activity.

Retain the screening ID with your internal subject reference. Retrieve the complete evidence through the documented retained-result workflow when authorized; the console summary deliberately does not print raw identity details. A later analyst decision must not overwrite the original screening outcome.

Handle failures and test the source-specific edge cases

Treat HTTP errors, timeouts, malformed JSON, missing fields, unknown statuses, and unavailable required coverage as incomplete checks. A 401 or 403 needs credential or scope correction. A 409 needs idempotency-conflict handling. A 429 needs its specific rate-limit or usage-cap treatment; it is not a no-match result.

Test similar names with different reliable birth years, overlapping year-only dates, and a source record with no comparable identifier. The absence of an identifier is unknown, not a conflict.

Substitute a test HttpMessageHandler and validate cancellation, HTTP failures, and JSON type mismatches. An empty matches array is valid only with the appropriate completed status; missing or object-shaped matches must fail.

• Verify both valid result states and inconsistent status/matches combinations.
• Retry an accepted operation only with its original key and unchanged payload.
• Keep missing identity facts unknown instead of inventing contradictory values.
• Route potential matches into review before the separate business decision.
• Keep secrets, submitted names, and raw error bodies out of routine logs.

Official references

• OFAC: sanctions list service (opens in a new tab)
• SanctionsKit: published OpenAPI contract (opens in a new tab)
• Microsoft: HttpClient (opens in a new tab)
• SanctionsKit: source coverage (opens in a new tab)