diff --git a/Iceshrimp.Backend/Core/Federation/WebFinger/Types.cs b/Iceshrimp.Backend/Core/Federation/WebFinger/Types.cs
index cd323252..dec8a674 100644
--- a/Iceshrimp.Backend/Core/Federation/WebFinger/Types.cs
+++ b/Iceshrimp.Backend/Core/Federation/WebFinger/Types.cs
@@ -4,11 +4,13 @@ using JR = System.Text.Json.Serialization.JsonRequiredAttribute;
 namespace Iceshrimp.Backend.Core.Federation.WebFinger;
 
 public sealed class Link {
-	[J("href"), JR] public string  Href { get; set; } = null!;
-	[J("rel")]      public string? Rel  { get; set; }
+	[J("rel"), JR] public string  Rel  { get; set; } = null!;
+	[J("type")]    public string? Type { get; set; } = null!;
+	[J("href")]    public string? Href { get; set; }
 }
 
 public sealed class WebFingerResponse {
-	[J("links"), JR]   public List<Link> Links   { get; set; } = null!;
-	[J("subject"), JR] public string     Subject { get; set; } = null!;
+	[J("links"), JR]   public List<Link>   Links   { get; set; } = null!;
+	[J("subject"), JR] public string       Subject { get; set; } = null!;
+	[J("aliases")]     public List<string> Aliases { get; set; } = [];
 }
\ No newline at end of file
diff --git a/Iceshrimp.Backend/Core/Federation/WebFinger/UserResolver.cs b/Iceshrimp.Backend/Core/Federation/WebFinger/UserResolver.cs
index 1607c5d2..cc278c4c 100644
--- a/Iceshrimp.Backend/Core/Federation/WebFinger/UserResolver.cs
+++ b/Iceshrimp.Backend/Core/Federation/WebFinger/UserResolver.cs
@@ -1,31 +1,89 @@
+using Iceshrimp.Backend.Core.Database;
 using Iceshrimp.Backend.Core.Database.Tables;
+using Iceshrimp.Backend.Core.Services;
 
 namespace Iceshrimp.Backend.Core.Federation.WebFinger;
 
-public class UserResolver(ILogger<UserResolver> logger) {
+public class UserResolver(ILogger<UserResolver> logger, UserService userSvc, DatabaseContext db) {
 	private static string AcctToDomain(string acct) =>
 		acct.StartsWith("acct:") && acct.Contains('@')
 			? acct[5..].Split('@')[1]
 			: throw new Exception("Invalid acct");
 
 	/*
-	 * Split domain logic:
-	 * 1. Get WebFinger response for query
-	 * 2. [...]
-	 * TODO: finish description and implement the rest
+	 * The full web finger algorithm:
+	 *
+	 * 1. WebFinger(input_uri), find the rel=self type=application/activity+json entry, that's ap_uri
+	 * 2. WebFinger(ap_uri), find the first acct: URI in [subject] + aliases, that's candidate_acct_uri
+	 * 3. WebFinger(candidate_acct_uri), validate it also points to ap_uri. If so, you have acct_uri
+	 * 4. Failing this, acct_uri = "acct:" + preferredUsername from AP actor + "@" + hostname from ap_uri (TODO: implement this)
+	 *
+	 * Avoid repeating WebFinger's with same URI for performance, TODO: optimize away validation checks when the domain matches
 	 */
 
-	public async Task<User> Resolve(string query) {
+	private async Task<(string Acct, string Uri)> WebFinger(string query) {
+		logger.LogDebug("Running WebFinger for query '{query}'", query);
+
 		var finger    = new WebFinger(query);
+		var responses = new Dictionary<string, WebFingerResponse>();
 		var fingerRes = await finger.Resolve();
 		if (fingerRes == null) throw new Exception($"Failed to WebFinger '{query}'");
-		if (finger.Domain != AcctToDomain(fingerRes.Subject)) {
-			logger.LogInformation("possible split domain deployment detected, repeating webfinger");
+		responses.Add(query, fingerRes);
 
-			finger    = new WebFinger(fingerRes.Subject);
+		var apUri = fingerRes.Links.FirstOrDefault(p => p.Rel == "self" && p.Type == "application/activity+json")
+		                     ?.Href;
+		if (apUri == null) throw new Exception($"WebFinger response for '{query}' didn't contain a candidate link");
+
+		fingerRes = responses.GetValueOrDefault(apUri);
+		if (fingerRes == null) {
+			logger.LogDebug("AP uri didn't match query, re-running WebFinger for '{apUri}'", apUri);
+
+			finger    = new WebFinger(apUri);
 			fingerRes = await finger.Resolve();
+
+			if (fingerRes == null) throw new Exception($"Failed to WebFinger '{apUri}'");
+			responses.Add(apUri, fingerRes);
 		}
 
-		throw new NotImplementedException("stub method return");
+		var acctUri = fingerRes.Aliases.Prepend(fingerRes.Subject).FirstOrDefault(p => p.StartsWith("acct:"));
+		if (acctUri == null) throw new Exception($"WebFinger response for '{apUri}' didn't contain any acct uris");
+
+		fingerRes = responses.GetValueOrDefault(acctUri);
+		if (fingerRes == null) {
+			logger.LogDebug("Acct uri didn't match query, re-running WebFinger for '{acctUri}'", acctUri);
+
+			finger    = new WebFinger(acctUri);
+			fingerRes = await finger.Resolve();
+
+			if (fingerRes == null) throw new Exception($"Failed to WebFinger '{acctUri}'");
+			responses.Add(acctUri, fingerRes);
+		}
+
+		var finalAcct = fingerRes.Subject;
+		var finalUri = fingerRes.Links.FirstOrDefault(p => p.Rel == "self" && p.Type == "application/activity+json")
+		                        ?.Href ?? throw new Exception("Final AP URI was null");
+
+		return (finalAcct, finalUri);
+	}
+
+	private static string NormalizeQuery(string query) => query.StartsWith("acct:") ? query[5..] : query;
+
+	public async Task<User> Resolve(string query) {
+		query = NormalizeQuery(query);
+		
+		// First, let's see if we already know the user
+		var user = await userSvc.GetUserFromQuery(query);
+		if (user != null) return user;
+
+		// We don't, so we need to run WebFinger
+		var (acct, uri) = await WebFinger(query);
+		
+		// Check the database again with the new data
+		if (uri != query) user = await userSvc.GetUserFromQuery(uri);
+		if (user == null && acct != query) await userSvc.GetUserFromQuery(acct);
+		if (user != null) return user;
+		
+		// Pass the job on to userSvc, which will create the user
+		return await userSvc.CreateUser(acct, uri);
 	}
 }
\ No newline at end of file
diff --git a/Iceshrimp.Backend/Core/Helpers/ServiceExtensions.cs b/Iceshrimp.Backend/Core/Helpers/ServiceExtensions.cs
index 656843e2..6b15b3bf 100644
--- a/Iceshrimp.Backend/Core/Helpers/ServiceExtensions.cs
+++ b/Iceshrimp.Backend/Core/Helpers/ServiceExtensions.cs
@@ -1,10 +1,12 @@
 using Iceshrimp.Backend.Core.Configuration;
+using Iceshrimp.Backend.Core.Federation.WebFinger;
 using Iceshrimp.Backend.Core.Services;
 
 namespace Iceshrimp.Backend.Core.Helpers;
 
 public static class ServiceExtensions {
 	public static void AddServices(this IServiceCollection services) {
+		services.AddScoped<UserResolver>();
 		services.AddScoped<UserService>();
 		services.AddScoped<NoteService>();
 	}
diff --git a/Iceshrimp.Backend/Core/Services/UserService.cs b/Iceshrimp.Backend/Core/Services/UserService.cs
index f86fc12a..d95d6842 100644
--- a/Iceshrimp.Backend/Core/Services/UserService.cs
+++ b/Iceshrimp.Backend/Core/Services/UserService.cs
@@ -1,10 +1,25 @@
 using Iceshrimp.Backend.Core.Database;
+using Iceshrimp.Backend.Core.Database.Tables;
+using Microsoft.EntityFrameworkCore;
 
 namespace Iceshrimp.Backend.Core.Services;
 
 public class UserService(ILogger<UserService> logger, DatabaseContext db) {
+	private static (string Username, string Host) AcctToTuple(string acct) {
+		if (!acct.StartsWith("acct:")) throw new Exception("Invalid query");
+		throw new NotImplementedException(); //FIXME
+	}
+	
+	public Task<User?> GetUserFromQuery(string query) {
+		if (query.StartsWith("http://") || query.StartsWith("https://")) {
+			return db.Users.FirstOrDefaultAsync(p => p.Uri == query);
+		}
 
-	public async Task CreateUser() {
-		
+		var tuple = AcctToTuple(query);
+		return db.Users.FirstOrDefaultAsync(p => p.Username == tuple.Username && p.Host == tuple.Host);
+	}
+	
+	public async Task<User> CreateUser(string uri, string acct) {
+		throw new NotImplementedException(); //FIXME
 	}
 }
\ No newline at end of file