diff --git a/AGENTS.md b/AGENTS.md
index 592ce7d..7f19918 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -14,6 +14,7 @@
 ## Tests
 
 - Suites live in `src/tests/`. They compile to `dist/tests` and ship in the package, so implementing modules can run them as a conformance suite; `src/tests/codec_helpers.ts` and `src/tests/helpers/` are part of that surface.
+- The model tests fetch routes from the `@antelopejs/api` module on `DECORATORS_TEST_API_PORT`, 5010 when unset. A project that runs the suite serves `api` on that same port, so suites that each set their own port run in parallel on one machine.
 - `pnpm test` builds once, then runs `ajs module test .` with the project in `src/antelope.test.ts`: a MongoDB memory server, `@antelopejs/mongodb` and `@antelopejs/api` from npm, cached in `.antelope/cache`. The first run needs network access to fetch them and the `mongod` binary.
 - `pnpm run checks` runs this whole suite. The documentation check runs only in CI (the `Check documentation` step of `ci-node.yml`). To run it locally, clone `AntelopeJS/tooling-configs` at `v0.0.9`, run `npm ci --prefix actions/docs --omit=dev`, then from this repository run `node <clone>/actions/docs/check.mjs --files $'README.md\ndocs' --typescript-project docs/tsconfig.json`.
 
diff --git a/src/antelope.test.ts b/src/antelope.test.ts
index 3aafb44..99a394c 100644
--- a/src/antelope.test.ts
+++ b/src/antelope.test.ts
@@ -1,7 +1,9 @@
 import { MongoMemoryServer } from "mongodb-memory-server-core";
 import { defineConfig } from "@antelopejs/interface-core/config";
+import { ApiPort } from "./tests/helpers/api-port";
 
 let mongod: MongoMemoryServer;
+const apiPort = ApiPort();
 
 export default defineConfig({
   name: "interface-database-decorators-test",
@@ -24,8 +26,8 @@ export default defineConfig({
         version: "1.6.0",
       },
       config: {
-        servers: [{ protocol: "http", host: "127.0.0.1", port: 5010 }],
-        publicBaseUrl: "http://127.0.0.1:5010",
+        servers: [{ protocol: "http", host: "127.0.0.1", port: apiPort }],
+        publicBaseUrl: `http://127.0.0.1:${apiPort}`,
       },
     },
   },
diff --git a/src/tests/api_port.test.ts b/src/tests/api_port.test.ts
new file mode 100644
index 0000000..802f171
--- /dev/null
+++ b/src/tests/api_port.test.ts
@@ -0,0 +1,20 @@
+import { expect } from "chai";
+
+import { API_PORT_VARIABLE, ApiPort } from "./helpers/api-port";
+
+describe("ApiPort", () => {
+  it("serves on 5010 when the variable is unset or empty", () => {
+    expect(ApiPort({})).to.equal(5010);
+    expect(ApiPort({ [API_PORT_VARIABLE]: "" })).to.equal(5010);
+  });
+  it("reads the port from the variable", () => {
+    expect(ApiPort({ [API_PORT_VARIABLE]: "5011" })).to.equal(5011);
+  });
+  it("rejects a value that is not a port", () => {
+    for (const raw of ["abc", "0", "65536", "50.1", " 5011", "-1"]) {
+      expect(() => ApiPort({ [API_PORT_VARIABLE]: raw }), raw).to.throw(
+        API_PORT_VARIABLE,
+      );
+    }
+  });
+});
diff --git a/src/tests/helpers/api-port.ts b/src/tests/helpers/api-port.ts
new file mode 100644
index 0000000..ad1afd8
--- /dev/null
+++ b/src/tests/helpers/api-port.ts
@@ -0,0 +1,26 @@
+/** The environment variable that sets the port the `@antelopejs/api` module serves the model tests on. */
+export const API_PORT_VARIABLE = "DECORATORS_TEST_API_PORT";
+
+const DEFAULT_API_PORT = 5010;
+const MAX_PORT = 65_535;
+
+/**
+ * The port the model tests fetch their routes from: `DECORATORS_TEST_API_PORT`, or 5010 when it is
+ * unset or empty. A backend serves `@antelopejs/api` on this port, so two suites on one machine run
+ * side by side when each sets its own.
+ *
+ * @throws When the variable is set to anything but a port number from 1 to 65535.
+ */
+export function ApiPort(env: NodeJS.ProcessEnv = process.env): number {
+  const raw = env[API_PORT_VARIABLE];
+  if (raw === undefined || raw === "") {
+    return DEFAULT_API_PORT;
+  }
+  const port = Number(raw);
+  if (!/^\d+$/.test(raw) || port < 1 || port > MAX_PORT) {
+    throw new Error(
+      `${API_PORT_VARIABLE} must be a port from 1 to ${MAX_PORT}, got "${raw}"`,
+    );
+  }
+  return port;
+}
diff --git a/src/tests/model.test.ts b/src/tests/model.test.ts
index db9e3e9..c6dc878 100644
--- a/src/tests/model.test.ts
+++ b/src/tests/model.test.ts
@@ -11,6 +11,9 @@ import {
 import { BasicDataModel, GetModel, Model } from "../model";
 
 import { asFieldType, numberCodec, stringCodec } from "./codec_helpers";
+import { ApiPort } from "./helpers/api-port";
+
+const apiUrl = `http://localhost:${ApiPort()}`;
 
 describe("Model - data operations", () => {
   it("creates basic data model", async () => {
@@ -150,7 +153,7 @@ describe("Model - data operations", () => {
       }
     }
 
-    const res = await fetch("http://localhost:5010/staticmodel");
+    const res = await fetch(`${apiUrl}/staticmodel`);
     expect(res.status, res.statusText).to.equal(200);
   });
   it("handles model with callback instance id", async () => {
@@ -171,9 +174,7 @@ describe("Model - data operations", () => {
       }
     }
 
-    const res = await fetch(
-      "http://localhost:5010/dynamicmodel/test-dynamic-model-db",
-    );
+    const res = await fetch(`${apiUrl}/dynamicmodel/test-dynamic-model-db`);
     expect(res.status, res.statusText).to.equal(200);
   });
 });