diff --git a/utils.js b/utils.js
index c8aa7b3..4a9feb7 100644
--- a/utils.js
+++ b/utils.js
@@ -1,4 +1,22 @@
 import { readFile } from "fs/promises";
+
+/**
+ * @typedef {Object} PersistedData
+ * @property {StoredRepo[]} repos - An array of repos.
+ * @property {number} totalRepos - The total number of repos.
+ * @property {string} org - The name of the Github organisation the repos belong to.
+ */
+
+/**
+ * @typedef {PersistedData} RepoData
+ * @property {UiRepo[]} repos - An array of repos.
+ */
+
+/**
+ * Maps the persisted repo data from storage to a format suitable for the UI
+ * @param {PersistedData} persistedData
+ * @returns {RepoData}
+ */
 export const mapRepoFromStorageToUi = (persistedData) => {
   const mappedRepos = persistedData.repos.map((repo) => {
     const newDate = new Date(repo.updatedAt).toLocaleDateString();
@@ -13,6 +31,11 @@ export const mapRepoFromStorageToUi = (persistedData) => {
   return { ...persistedData, repos: mappedRepos, totalRepos };
 };
 
+/**
+ * Reads the persisted repo data from a JSON file
+ * @param {string} filePath - The path to the file to read from
+ * @returns {PersistedData}
+ */
 export const getReposFromJson = async (filePath) => {
   const reposJson = await readFile(filePath, { encoding: "utf-8" });
   const persistedData = JSON.parse(reposJson);
@@ -20,6 +43,45 @@ export const getReposFromJson = async (filePath) => {
   return persistedData;
 };
 
+/**
+ * @typedef {Object} ApiRepo
+ * @property {string} name - The name of the repo Eg "dalmation".
+ * @property {string} description - A brief description of the repo.
+ * @property {string} html_url - The URL to the repo on GitHub for humans.
+ * @property {string} pulls_url - The API url to get more info on pull requests for this repo.
+ * @property {string} issues_url - The API url to get more info on issues for this repo.
+ * @property {string} updated_at - The date the repo was last updated in ISO8601 format.
+ * @property {string} language - The primary language the repo is written in.
+ * @property {string[]} topics - An array of topics associated with the repo - conventially in dxw this is used to list the owners of the repo (EG govpress, delivery-plus).
+ * @property {number} open_issues - The number of open issues on the repo.
+ * @property {string[]} dependencies - An array of dependencies used by the repo.
+ */
+
+/**
+ * @typedef {Object} StoredRepo
+ * @property {string} name - The name of the repo Eg "dalmation".
+ * @property {string} description - A brief description of the repo.
+ * @property {string} htmlUrl - The URL to the repo on GitHub for humans.
+ * @property {string} apiUrl - The URL to the repo on GitHub for computers.
+ * @property {string} pullsUrl - The API url to get more info on pull requests for this repo.
+ * @property {string} issuesUrl - The API url to get more info on issues for this repo.
+ * @property {string} updatedAt - The date the repo was last updated in ISO8601 format.
+ * @property {string} language - The primary language the repo is written in.
+ * @property {string[]} topics - An array of topics associated with the repo - conventially in dxw this is used to list the owners of the repo (EG govpress, delivery-plus).
+ * @property {number} openIssues - The number of open issues on the repo.
+ * @property {string[]} dependencies - An array of dependencies used by the repo.
+ */
+
+/**
+ * @typedef {StoredRepo} UiRepo
+ * @property {Date} date - The date the repo was last updated in JS date format.
+ */
+
+/**
+ * Maps from an API repo to a StoredRepo
+ * @param {ApiRepo} repo
+ * @returns {StoredRepo}
+ */
 export const mapRepoFromApiForStorage = (repo) => ({
   name: repo.name,
   description: repo.description,