Google Custom Search API in C# and .NET

Google.Apis.CustomSearchAPI.v1: the same call with one more property

This is code that calls Google today, with the Google.Apis.CustomSearchAPI.v1 NuGet package:

var service = new CustomSearchAPIService(new BaseClientService.Initializer
{
    ApiKey = Environment.GetEnvironmentVariable("GOOGLE_API_KEY"),
    ApplicationName = "my-app",
});

var request = service.Cse.List();
request.Q = "web data api";
request.Cx = Environment.GetEnvironmentVariable("GOOGLE_CSE_ID");
var result = request.Execute();

And the same program on SpecStream. BaseUri on BaseClientService.Initializer is set to https://api.specstream.ai/ and ApiKey holds a SpecStream key. service.Cse.List(), Q, Cx, Execute() and the code that reads result.Items stay as they were. This is the call that ran on November 10, 2026 with 1.78.0.3520 and printed 10 items.

using Google.Apis.CustomSearchAPI.v1;
using Google.Apis.Services;

var service = new CustomSearchAPIService(new BaseClientService.Initializer
{
    ApiKey = Environment.GetEnvironmentVariable("SPECSTREAM_API_KEY"),
    BaseUri = "https://api.specstream.ai/", // the one changed option
    ApplicationName = "my-app",
});

var request = service.Cse.List();
request.Q = "web data api";
request.Cx = Environment.GetEnvironmentVariable("GOOGLE_CSE_ID"); // any value is accepted
var result = request.Execute();

Console.WriteLine($"{result.Items.Count} items");
foreach (var item in result.Items)
    Console.WriteLine($"{item.Title} {item.Link}");

The same call with HttpClient, no package to add

The reply is Google's JSON: items with title, link and snippet, searchInformation.totalResults and queries.nextPage. A search that finds nothing has no items, as on Google, so the code checks for it with TryGetProperty.

using System.Net;
using System.Text.Json;

var key = Environment.GetEnvironmentVariable("SPECSTREAM_API_KEY");
var q = Uri.EscapeDataString("open source vector databases");
var url = $"https://api.specstream.ai/customsearch/v1?key={key}&cx=any&q={q}&num=10";

using var http = new HttpClient();
using var response = await http.GetAsync(url);
if (response.StatusCode == HttpStatusCode.TooManyRequests)
{
    Console.WriteLine($"busy, retry after {response.Headers.RetryAfter}");
    return;
}

using var doc = JsonDocument.Parse(await response.Content.ReadAsStringAsync());
var root = doc.RootElement;
if (root.TryGetProperty("error", out var error))
    throw new Exception(error.GetProperty("message").GetString());

if (root.TryGetProperty("items", out var items))
{
    foreach (var item in items.EnumerateArray())
        Console.WriteLine($"{item.GetProperty("title")} {item.GetProperty("link")}");
}

An error comes back in Google's shape, {"error": {"code", "message", "errors", "status"}}, so the client library's GoogleApiException and code that reads error.message keep working.

Paging with start and queries.nextPage

start is 1-based, as on Google. Each reply carries queries.nextPage while more results exist, so the loop stops when it is gone. Each page of up to 10 results is one search at $0.005.

// Page with Start: 1, 11, 21. Each page of up to 10 is one search.
foreach (var start in new long[] { 1, 11, 21 })
{
    var page = service.Cse.List();
    page.Q = "open source vector databases";
    page.Cx = "any";
    page.Num = 10;
    page.Start = start;
    var reply = page.Execute();
    foreach (var item in reply.Items ?? new List<Google.Apis.CustomSearchAPI.v1.Data.Result>())
        Console.WriteLine(item.Link);
    if (reply.Queries?.NextPage == null) break;
}

The parameters your code already sends

The route honours nine parameters as Google does: q, num, start, hq, exactTerms, orTerms, excludeTerms, siteSearch and siteSearchFilter. fileType, dateRestrict, lowRange and highRange are accepted and not applied, so code that sends them still gets results. Any cx is accepted. Every parameter and every field is listed in the migration guide.

$5 per 1,000 searches and the best published scores

A call of up to 10 results is $0.005, with no cap of 10,000 a day, and a busy call that answers 429 is not charged. SpecStream scores 97.9 F-score on all 1,000 SimpleQA Verified questions (978 correct) and 64.0 item F1 and 43.4 row F1 on all 200 WideSearch tasks. On production on November 9, 2026, the median search took 0.82 s at 1 search a second and 1.07 s at 20 a second.

What is kept from a search

On a key with zero retention, only the charge's account, key, request ID, price and time: no request text and no answer after the reply. Set "zero_retention": true when you create the key, or later on the same key.

The same key reads pages and returns rows

The Extract API reads up to 20 pages or documents a call at $0.80 per 1,000 pages and scores 0.908 F1 on WCXB. Deep Search takes a request in plain words and returns every match as structured rows at 5¢, 15¢ or $1 a row, with the most a run can cost quoted before it starts.

Vertex AI Search

The product Google points Custom Search customers to, for up to 50 domains, at $1.50 per 1,000 queries on Search Standard Edition. Its call is a POST to discoveryengine.googleapis.com with a different request and reply, so the .NET code that reads items is rewritten. SpecStream answers the cse.list call you already send, across the whole web.

Grounding with Google Search in the Gemini API

A Gemini model runs the searches and writes an answer grounded in the results, at $14 per 1,000 search requests on Gemini 3 and newer after 5,000 free a month. Your code receives the model's answer. SpecStream returns items with title, link and snippet at $5 per 1,000.

Brave Search API

A search API on Brave's own index at $5 per 1,000 requests, with $5 in free credits every month and 50 queries per second. Brave's own guide says moving from Google means swapping the endpoint and updating how you read the response. On SpecStream the code that reads Google's response stays as it is.