diff --git a/.gitignore b/.gitignore
index af1f8a9..067cc48 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,6 +5,7 @@ coverage/
 .env
 .env.*
 !.env.example
+config/verifications.yaml
 .DS_Store
 .idea/
 .vscode/
diff --git a/src/events/ready.ts b/src/events/ready.ts
index 4d30764..f25fa78 100644
--- a/src/events/ready.ts
+++ b/src/events/ready.ts
@@ -1,9 +1,10 @@
 import { type Client, Events } from "discord.js";
 import type { Config } from "../config.js";
 import { logger } from "../logger.js";
+import { type DiscordRestLike, runSweep } from "../sweep.js";
 
-export function registerReady(client: Client, cfg: Config): void {
-  client.once(Events.ClientReady, (readyClient) => {
+export function registerReady(client: Client, cfg: Config, rest: DiscordRestLike): void {
+  client.once(Events.ClientReady, async (readyClient) => {
     const guilds = readyClient.guilds.cache.map((g) => ({ id: g.id, name: g.name }));
     logger.info(
       {
@@ -14,5 +15,16 @@ export function registerReady(client: Client, cfg: Config): void {
       },
       "ready",
     );
+
+    if (!cfg.sweep.on_startup) return;
+
+    for (const v of cfg.verifications) {
+      try {
+        const result = await runSweep(rest, v);
+        logger.info({ verification: v.name, ...result }, "sweep complete");
+      } catch (err) {
+        logger.error({ err, verification: v.name }, "sweep failed");
+      }
+    }
   });
 }
diff --git a/src/index.ts b/src/index.ts
index 1c73919..61cafb9 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -3,6 +3,7 @@ import { loadConfig } from "./config.js";
 import { loadEnv } from "./env.js";
 import { registerReady } from "./events/ready.js";
 import { logger } from "./logger.js";
+import { createDiscordRest } from "./rest.js";
 
 async function main(): Promise<void> {
   const env = loadEnv();
@@ -13,7 +14,8 @@ async function main(): Promise<void> {
   );
 
   const client = createClient();
-  registerReady(client, cfg);
+  const rest = createDiscordRest(client.rest);
+  registerReady(client, cfg, rest);
 
   client.on("error", (err) => {
     logger.error({ err }, "client error");
diff --git a/src/rest.ts b/src/rest.ts
new file mode 100644
index 0000000..62ccc6e
--- /dev/null
+++ b/src/rest.ts
@@ -0,0 +1,36 @@
+import { DiscordAPIError, type REST, Routes } from "discord.js";
+import type { DiscordRestLike, MemberInfo, Reactor } from "./sweep.js";
+
+const UNKNOWN_MEMBER = 10007;
+
+export function createDiscordRest(rest: REST): DiscordRestLike {
+  return {
+    async listReactors({ channelId, messageId, emoji, after, limit = 100 }) {
+      const query = new URLSearchParams({ limit: String(limit) });
+      if (after) query.set("after", after);
+      const data = (await rest.get(
+        Routes.channelMessageReaction(channelId, messageId, encodeURIComponent(emoji)),
+        { query },
+      )) as Array<{ id: string; username: string }>;
+      return data.map<Reactor>((u) => ({ id: u.id, username: u.username }));
+    },
+
+    async getMember({ guildId, userId }) {
+      try {
+        const data = (await rest.get(Routes.guildMember(guildId, userId))) as {
+          user: { id: string };
+          roles: string[];
+        };
+        const member: MemberInfo = { id: data.user.id, roles: data.roles };
+        return member;
+      } catch (err) {
+        if (err instanceof DiscordAPIError && err.code === UNKNOWN_MEMBER) return null;
+        throw err;
+      }
+    },
+
+    async addMemberRole({ guildId, userId, roleId }) {
+      await rest.put(Routes.guildMemberRole(guildId, userId, roleId));
+    },
+  };
+}
diff --git a/src/sweep.ts b/src/sweep.ts
new file mode 100644
index 0000000..62e4159
--- /dev/null
+++ b/src/sweep.ts
@@ -0,0 +1,125 @@
+import type { Verification } from "./config.js";
+import { logger } from "./logger.js";
+
+export interface SweepResult {
+  reactors: number;
+  granted: number;
+  alreadyHadRole: number;
+  notInGuild: number;
+  errors: number;
+}
+
+export interface Reactor {
+  id: string;
+  username: string;
+}
+
+export interface MemberInfo {
+  id: string;
+  roles: readonly string[];
+}
+
+export interface DiscordRestLike {
+  listReactors(opts: {
+    channelId: string;
+    messageId: string;
+    emoji: string;
+    after?: string;
+    limit?: number;
+  }): Promise<Reactor[]>;
+  // Returns null when the user is not a member of the guild.
+  getMember(opts: { guildId: string; userId: string }): Promise<MemberInfo | null>;
+  addMemberRole(opts: { guildId: string; userId: string; roleId: string }): Promise<void>;
+}
+
+const PAGE_SIZE = 100;
+
+export async function runSweep(rest: DiscordRestLike, v: Verification): Promise<SweepResult> {
+  const result: SweepResult = {
+    reactors: 0,
+    granted: 0,
+    alreadyHadRole: 0,
+    notInGuild: 0,
+    errors: 0,
+  };
+
+  const reactors = await collectReactors(rest, v);
+  result.reactors = reactors.length;
+
+  for (const reactor of reactors) {
+    const outcome = await processReactor(rest, v, reactor);
+    if (outcome === "granted") result.granted += 1;
+    else if (outcome === "already") result.alreadyHadRole += 1;
+    else if (outcome === "notInGuild") result.notInGuild += 1;
+    else result.errors += 1;
+  }
+
+  return result;
+}
+
+async function collectReactors(rest: DiscordRestLike, v: Verification): Promise<Reactor[]> {
+  const all: Reactor[] = [];
+  let after: string | undefined;
+  let done = false;
+  while (!done) {
+    const page = await rest.listReactors({
+      channelId: v.channel_id,
+      messageId: v.message_id,
+      emoji: v.emoji,
+      ...(after === undefined ? {} : { after }),
+      limit: PAGE_SIZE,
+    });
+    all.push(...page);
+    if (page.length < PAGE_SIZE) {
+      done = true;
+    } else {
+      after = page[page.length - 1]?.id;
+    }
+  }
+  return all;
+}
+
+type Outcome = "granted" | "already" | "notInGuild" | "error";
+
+async function processReactor(
+  rest: DiscordRestLike,
+  v: Verification,
+  reactor: Reactor,
+): Promise<Outcome> {
+  let member: MemberInfo | null;
+  try {
+    member = await rest.getMember({ guildId: v.guild_id, userId: reactor.id });
+  } catch (err) {
+    logger.error(
+      { err, verification: v.name, userId: reactor.id, username: reactor.username },
+      "sweep: failed to fetch member",
+    );
+    return "error";
+  }
+  if (!member) return "notInGuild";
+  if (member.roles.includes(v.role_id)) return "already";
+
+  try {
+    await rest.addMemberRole({
+      guildId: v.guild_id,
+      userId: reactor.id,
+      roleId: v.role_id,
+    });
+    logger.info(
+      {
+        verification: v.name,
+        userId: reactor.id,
+        username: reactor.username,
+        roleId: v.role_id,
+      },
+      "sweep: granted role",
+    );
+    return "granted";
+  } catch (err) {
+    logger.error(
+      { err, verification: v.name, userId: reactor.id, username: reactor.username },
+      "sweep: failed to add role",
+    );
+    return "error";
+  }
+}
diff --git a/test/sweep.test.ts b/test/sweep.test.ts
new file mode 100644
index 0000000..08e1fb4
--- /dev/null
+++ b/test/sweep.test.ts
@@ -0,0 +1,159 @@
+import { describe, expect, it, vi } from "vitest";
+import type { Verification } from "../src/config.js";
+import { type DiscordRestLike, type Reactor, runSweep } from "../src/sweep.js";
+
+const verification: Verification = {
+  name: "test",
+  guild_id: "1000000000000000001",
+  channel_id: "1000000000000000002",
+  message_id: "1000000000000000003",
+  emoji: "✅",
+  role_id: "1000000000000000004",
+  on_remove: "keep",
+};
+
+function reactor(id: string): Reactor {
+  return { id, username: `user${id}` };
+}
+
+function mockRest(overrides: Partial<DiscordRestLike> = {}): DiscordRestLike {
+  return {
+    listReactors: vi.fn().mockResolvedValue([]),
+    getMember: vi.fn().mockResolvedValue(null),
+    addMemberRole: vi.fn().mockResolvedValue(undefined),
+    ...overrides,
+  };
+}
+
+describe("runSweep", () => {
+  it("returns zeroed counts when no reactors", async () => {
+    const result = await runSweep(mockRest(), verification);
+    expect(result).toEqual({
+      reactors: 0,
+      granted: 0,
+      alreadyHadRole: 0,
+      notInGuild: 0,
+      errors: 0,
+    });
+  });
+
+  it("grants role to a reactor who doesn't have it", async () => {
+    const rest = mockRest({
+      listReactors: vi
+        .fn()
+        .mockResolvedValueOnce([reactor("1")])
+        .mockResolvedValueOnce([]),
+      getMember: vi.fn().mockResolvedValue({ id: "1", roles: [] }),
+    });
+    const result = await runSweep(rest, verification);
+    expect(result.granted).toBe(1);
+    expect(result.reactors).toBe(1);
+    expect(rest.addMemberRole).toHaveBeenCalledWith({
+      guildId: verification.guild_id,
+      userId: "1",
+      roleId: verification.role_id,
+    });
+  });
+
+  it("skips a reactor who already has the role", async () => {
+    const rest = mockRest({
+      listReactors: vi
+        .fn()
+        .mockResolvedValueOnce([reactor("1")])
+        .mockResolvedValueOnce([]),
+      getMember: vi.fn().mockResolvedValue({ id: "1", roles: [verification.role_id] }),
+    });
+    const result = await runSweep(rest, verification);
+    expect(result.alreadyHadRole).toBe(1);
+    expect(result.granted).toBe(0);
+    expect(rest.addMemberRole).not.toHaveBeenCalled();
+  });
+
+  it("counts reactors who left the guild", async () => {
+    const rest = mockRest({
+      listReactors: vi
+        .fn()
+        .mockResolvedValueOnce([reactor("1")])
+        .mockResolvedValueOnce([]),
+      getMember: vi.fn().mockResolvedValue(null),
+    });
+    const result = await runSweep(rest, verification);
+    expect(result.notInGuild).toBe(1);
+    expect(rest.addMemberRole).not.toHaveBeenCalled();
+  });
+
+  it("paginates through multiple pages", async () => {
+    const page1 = Array.from({ length: 100 }, (_, i) => reactor(String(i + 1)));
+    const page2 = [reactor("101"), reactor("102")];
+    const listReactors = vi.fn().mockResolvedValueOnce(page1).mockResolvedValueOnce(page2);
+    const rest = mockRest({
+      listReactors,
+      getMember: vi.fn().mockResolvedValue({ id: "x", roles: [] }),
+    });
+    const result = await runSweep(rest, verification);
+    expect(result.reactors).toBe(102);
+    expect(result.granted).toBe(102);
+    expect(listReactors).toHaveBeenCalledTimes(2);
+    expect(listReactors.mock.calls[1]?.[0]).toMatchObject({ after: "100" });
+  });
+
+  it("stops paginating when an exact-multiple page is followed by an empty page", async () => {
+    const page1 = Array.from({ length: 100 }, (_, i) => reactor(String(i + 1)));
+    const listReactors = vi.fn().mockResolvedValueOnce(page1).mockResolvedValueOnce([]);
+    const rest = mockRest({
+      listReactors,
+      getMember: vi.fn().mockResolvedValue({ id: "x", roles: [verification.role_id] }),
+    });
+    const result = await runSweep(rest, verification);
+    expect(result.reactors).toBe(100);
+    expect(listReactors).toHaveBeenCalledTimes(2);
+  });
+
+  it("counts errors when getMember throws", async () => {
+    const rest = mockRest({
+      listReactors: vi
+        .fn()
+        .mockResolvedValueOnce([reactor("1")])
+        .mockResolvedValueOnce([]),
+      getMember: vi.fn().mockRejectedValue(new Error("boom")),
+    });
+    const result = await runSweep(rest, verification);
+    expect(result.errors).toBe(1);
+    expect(result.granted).toBe(0);
+  });
+
+  it("counts errors when addMemberRole throws", async () => {
+    const rest = mockRest({
+      listReactors: vi
+        .fn()
+        .mockResolvedValueOnce([reactor("1")])
+        .mockResolvedValueOnce([]),
+      getMember: vi.fn().mockResolvedValue({ id: "1", roles: [] }),
+      addMemberRole: vi.fn().mockRejectedValue(new Error("forbidden")),
+    });
+    const result = await runSweep(rest, verification);
+    expect(result.errors).toBe(1);
+    expect(result.granted).toBe(0);
+  });
+
+  it("mixes outcomes across many reactors correctly", async () => {
+    const reactors = [reactor("1"), reactor("2"), reactor("3"), reactor("4")];
+    const rest = mockRest({
+      listReactors: vi.fn().mockResolvedValueOnce(reactors).mockResolvedValueOnce([]),
+      getMember: vi
+        .fn()
+        .mockResolvedValueOnce({ id: "1", roles: [] }) // grant
+        .mockResolvedValueOnce({ id: "2", roles: [verification.role_id] }) // already
+        .mockResolvedValueOnce(null) // not in guild
+        .mockRejectedValueOnce(new Error("boom")), // error
+    });
+    const result = await runSweep(rest, verification);
+    expect(result).toEqual({
+      reactors: 4,
+      granted: 1,
+      alreadyHadRole: 1,
+      notInGuild: 1,
+      errors: 1,
+    });
+  });
+});