diff --git a/api/README.md b/api/README.md
index d2281d1..2c8b6fb 100644
--- a/api/README.md
+++ b/api/README.md
@@ -4,7 +4,7 @@ A Fastify-based API service for DeFlock handling non-OSM related backend logic.
 
 ## Endpoints
 - `/geocode?query=...` — Geocode a location
-- `/sponsors/github?username=...` — Get GitHub sponsors
+- `/sponsors/github` — Get GitHub sponsors
 - `/healthcheck` — Health check
 
 ## Development
diff --git a/api/server.ts b/api/server.ts
index 34ad88c..e899bd7 100644
--- a/api/server.ts
+++ b/api/server.ts
@@ -205,21 +205,14 @@ const start = async () => {
 
   server.get('/sponsors/github', {
     schema: {
-      querystring: {
-        type: 'object',
-        properties: {
-          username: { type: 'string', default: 'frillweeman' },
-        },
-      },
       response: {
         200: SponsorsResponseSchema,
         500: { type: 'object', properties: { error: { type: 'string' } } },
       },
     },
   }, async (request, reply) => {
-    const { username } = request.query as { username?: string };
     reply.header('Cache-Control', 'public, max-age=60, s-maxage=600');
-    const result = await githubClient.getSponsors(username || 'frillweeman');
+    const result = await githubClient.getSponsors();
     return result;
   });
 
diff --git a/api/services/GithubClient.test.ts b/api/services/GithubClient.test.ts
new file mode 100644
index 0000000..7b3df30
--- /dev/null
+++ b/api/services/GithubClient.test.ts
@@ -0,0 +1,60 @@
+import { describe, it, expect, afterEach, mock } from 'bun:test';
+import { GithubClient, buildSponsorsQuery } from './GithubClient';
+
+describe('buildSponsorsQuery', () => {
+  it('parameterizes the username via a $username GraphQL variable instead of interpolating it', () => {
+    const { query, variables } = buildSponsorsQuery();
+    expect(query).toContain('query($username: String!)');
+    expect(query).toContain('user(login: $username)');
+    expect(variables).toEqual({ username: 'frillweeman' });
+  });
+
+  it('requests sponsorships and the expected sponsor fields', () => {
+    const { query } = buildSponsorsQuery();
+    expect(query).toContain('sponsorshipsAsMaintainer(first: 100)');
+    for (const field of ['login', 'name', 'avatarUrl', 'url']) {
+      expect(query).toContain(field);
+    }
+  });
+});
+
+describe('GithubClient.getSponsors', () => {
+  const originalFetch = global.fetch;
+
+  afterEach(() => {
+    global.fetch = originalFetch;
+  });
+
+  it('sends exactly the query and variables built by buildSponsorsQuery', async () => {
+    let capturedBody: any;
+    global.fetch = mock(async (_url: string, init: RequestInit) => {
+      capturedBody = JSON.parse(init.body as string);
+      return new Response(JSON.stringify({ data: { user: { sponsorshipsAsMaintainer: { nodes: [] } } } }));
+    }) as unknown as typeof fetch;
+
+    const client = new GithubClient();
+    await client.getSponsors();
+
+    expect(capturedBody).toEqual(buildSponsorsQuery());
+  });
+
+  it('returns the sponsor nodes from the response', async () => {
+    const nodes = [{ sponsor: { login: 'someone', name: 'Someone', avatarUrl: 'https://example.com/a.png', url: 'https://github.com/someone' } }];
+    global.fetch = mock(async () =>
+      new Response(JSON.stringify({ data: { user: { sponsorshipsAsMaintainer: { nodes } } } }))
+    ) as unknown as typeof fetch;
+
+    const client = new GithubClient();
+    const result = await client.getSponsors();
+
+    expect(result).toEqual(nodes);
+  });
+
+  it('throws when the GitHub API responds with a non-OK status', async () => {
+    global.fetch = mock(async () => new Response('', { status: 500 })) as unknown as typeof fetch;
+
+    const client = new GithubClient();
+
+    await expect(client.getSponsors()).rejects.toThrow('Failed to get sponsors: 500');
+  });
+});
\ No newline at end of file
diff --git a/api/services/GithubClient.ts b/api/services/GithubClient.ts
index c37c571..f9ccaa1 100644
--- a/api/services/GithubClient.ts
+++ b/api/services/GithubClient.ts
@@ -3,6 +3,7 @@ import { Type, Static } from '@sinclair/typebox';
 
 const GITHUB_TOKEN = process.env.GITHUB_TOKEN || '';
 const graphQLEndpoint = 'https://api.github.com/graphql';
+const MAINTAINER_USERNAME = 'frillweeman';
 
 export const SponsorSchema = Type.Object({
   sponsor: Type.Object({
@@ -17,10 +18,19 @@ export type Sponsor = Static<typeof SponsorSchema>;
 
 export const SponsorsResponseSchema = Type.Array(SponsorSchema);
 
+// The maintainer's username is passed as a GraphQL variable rather than
+// interpolated into the query string. It's a hardcoded constant today, but
+// keeping this indirection means a future caller-supplied value can never
+// break out of the query text the way the old string-interpolated version did.
+export const buildSponsorsQuery = (): { query: string; variables: { username: string } } => ({
+  query: `query($username: String!) { user(login: $username) { sponsorshipsAsMaintainer(first: 100) { nodes { sponsor { login name avatarUrl url } } } } }`,
+  variables: { username: MAINTAINER_USERNAME },
+});
+
 export class GithubClient {
-  async getSponsors(username: string): Promise<Sponsor[]> {
-    const query = `query { user(login: "${username}") { sponsorshipsAsMaintainer(first: 100) { nodes { sponsor { login name avatarUrl url } } } } }`;
-    const body = JSON.stringify({ query, variables: '' });
+  async getSponsors(): Promise<Sponsor[]> {
+    const { query, variables } = buildSponsorsQuery();
+    const body = JSON.stringify({ query, variables });
     const response = await fetch(graphQLEndpoint, {
       method: 'POST',
       headers: {