diff --git a/index.js b/index.js
new file mode 100644
index 0000000..5ed541f
--- /dev/null
+++ b/index.js
@@ -0,0 +1,129 @@
+const core = require("@actions/core");
+const github = require("@actions/github");
+const semver = require("semver");
+const tc = require("@actions/tool-cache");
+const fs = require("fs");
+const retry = require("async-retry");
+
+const NEXTFLOW_REPO = { owner: "nextflow-io", repo: "nextflow" };
+
+async function all_nf_releases(ok) {
+  const { data: releases } = await ok.rest.repos.listReleases(NEXTFLOW_REPO);
+
+  return releases;
+}
+
+async function latest_stable_release_data(ok) {
+  const { data: stable_release } = await ok.rest.repos.getLatestRelease(
+    NEXTFLOW_REPO
+  );
+
+  return stable_release;
+}
+
+async function release_data(version, ok) {
+  // Setup tag-based filtering
+  filter = (r) => {
+    return semver.satisfies(r.tag_name, version, true);
+  };
+
+  // Check if the user passed a 'latest*' tag, and override filtering
+  // accordingly
+  if (version.includes("latest")) {
+    if (version.includes("-everything")) {
+      // No filtering
+      filter = (r) => {
+        return true;
+      };
+    } else if (version.includes("-edge")) {
+      filter = (r) => {
+        return r.tag_name.endsWith("-edge");
+      };
+    } else {
+      // This is special: passing 'latest' or 'latest-stable' allows us to use
+      // the latest stable GitHub release direct from the API
+      stable_release = await latest_stable_release_data(ok);
+      return stable_release;
+    }
+  }
+
+  // Get all the releases
+  const all_releases = await all_nf_releases(ok);
+
+  matching_releases = all_releases.filter(filter);
+
+  matching_releases.sort(function (x, y) {
+    semver.compare(x.tag_name, y.tag_name, true);
+  });
+
+  return matching_releases[0];
+}
+
+function nextflow_bin_url(release, get_all) {
+  const release_assets = release.assets;
+  const all_asset = release_assets.filter((a) => {
+    return a.browser_download_url.endsWith("-all");
+  })[0];
+  const regular_asset = release_assets.filter((a) => {
+    return a.name == "nextflow";
+  })[0];
+
+  const dl_asset = get_all ? all_asset : regular_asset;
+
+  return dl_asset.browser_download_url;
+}
+
+async function run() {
+  // Setup the API
+  let octokit = {};
+  try {
+    const token = core.getInput("token");
+    octokit = github.getOctokit(token);
+  } catch (e) {
+    core.setFailed(
+      `Could not authenticate to GitHub Releases API with provided token\n${e.message}`
+    );
+  }
+
+  // Get the release info for the desired release
+  let release = {};
+  try {
+    const version = core.getInput("version");
+    release = release_data(version, octokit);
+  } catch (e) {
+    core.setFailed(
+      `Could not retrieve Nextflow release matching ${version}.\n${e.message}`
+    );
+  }
+
+  // Get the download url for the desired release
+  let url = "";
+  try {
+    const get_all = core.getBooleanInput("all");
+    url = nextflow_bin_url(release, get_all);
+  } catch (e) {
+    core.setFailed(`Could not parse the download URL\n${e.message}`);
+  }
+
+  // Download Nextflow and add it to path
+  let nf_path = "";
+  try {
+    const temp_install_dir = fs.mkdtempSync(`nextflow`);
+    nf_path = await retry(
+      async (bail) => {
+        return await tc.downloadTool(url, `${temp_install_dir}/nextflow`);
+      },
+      {
+        onRetry: (err) => {
+          core.debug(`Download of ${url} failed, trying again. Error: ${err}`);
+        },
+      }
+    );
+
+    core.addPath(nf_path);
+  } catch (e) {
+    core.setFailed(e.message);
+  }
+}
+
+run();