First draft of firestore-basics skill #9719

joehan · 2026-01-08T18:35:24Z

Slightly more polished draft of the firestore-basics skill. It covers:

Provisioning a DB and setting up your firebase.json, rules, and index filkes
Setting up SDKs on each platform, and a bunch of usage examples
A bunch of usage examples of security rules common patterns

TODOs

Add compatibility field that tells agents to instal the CLI if possible
Add more in depth examples to security rules
Add deployment section to provisioning.md
Test and iterate - can we reduce token usage by putting the most basic CUJs directly in SKILL.md?

gemini-code-assist · 2026-01-08T18:35:41Z

Summary of Changes

Hello @joehan, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces the initial draft of a new 'firestore-basics' skill. Its primary goal is to serve as a comprehensive resource for users looking to understand and implement Cloud Firestore, covering essential aspects from initial setup and configuration to securing data with rules and integrating the SDK into applications.

Highlights

New Firestore Basics Skill: Introduced a new skill named firestore-basics which serves as a comprehensive guide for Cloud Firestore.
Provisioning Guide: Added detailed documentation for setting up Cloud Firestore, covering Firebase CLI initialization, firebase.json configuration, and local emulator usage.
Security Rules Documentation: Provided explanations for Firestore Security Rules, including basic structure, common patterns (locked, test, auth required, user-specific), and deployment instructions.
SDK Usage Examples: Included guidance and code snippets for initializing and using the Firestore Web Modular SDK, connecting to the emulator, and performing basic data operations like adding, reading, and listening for real-time updates.

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gemini-code-assist

Code Review

This pull request introduces a new 'firestore-basics' skill, providing a foundational guide to Cloud Firestore. The skill is well-structured into provisioning, security rules, and SDK usage. My review includes suggestions to enhance the examples and documentation to make them more practical for users. Specifically, I've recommended improving how data is logged in the SDK examples, adding more advanced security rule patterns like data validation and separated read/write access, and including a section on deploying Firestore configurations. These suggestions align with the TODOs mentioned in the pull request description and aim to make the skill more complete.

skills/firestore-basics/references/provisioning.md

skills/firestore-basics/references/sdk_usage.md

skills/firestore-basics/references/security_rules.md

joehan · 2026-01-09T17:30:51Z

/gemini review

gemini-code-assist

Code Review

This pull request introduces a new 'firestore-basics' skill, providing comprehensive documentation and code examples for web, Android, and iOS. The content is well-structured and covers key aspects of Firestore, including provisioning, security rules, SDK usage, and indexes. My review focuses on improving the correctness and clarity of the code snippets and documentation. I've identified several issues, such as incorrect API usage in the Android SDK examples, unsafe coding practices like force-unwrapping in Swift, and formatting problems in the markdown files. I've provided specific suggestions to fix these issues, which will enhance the quality and reliability of the skill for developers.

gemini-code-assist · 2026-01-09T17:33:16Z

skills/firestore-basics/references/android_sdk_usage.md

+
+```kotlin
+db.collection("cities")
+    .orderBy("name", Query.Direction.KEY_ASCENDING)


Query.Direction.KEY_ASCENDING is not a valid enum member and will cause a compilation error. The correct values are Query.Direction.ASCENDING and Query.Direction.DESCENDING.

Suggested change

.orderBy("name", Query.Direction.KEY_ASCENDING)

.orderBy("name", Query.Direction.ASCENDING)

gemini-code-assist · 2026-01-09T17:33:16Z

skills/firestore-basics/references/security_rules.md

+```
+  match /databases/{database}/documents {
+    // Allow access based on email domain
+    match /some_collection/{document} {
+     allow read: if request.auth != null
+                 && request.auth.email_verified
+                 && request.auth.email.endsWith('@example.com')
+    }
+  }
+```


The example for allowing access to users with verified emails contains a redundant and incorrect nested match /databases/{database}/documents block. Security rules files should only have one top-level service block, and match blocks for paths are nested within that. This extra nesting will cause a syntax error.

Suggested change

```

match /databases/{database}/documents {

// Allow access based on email domain

match /some_collection/{document} {

allow read: if request.auth != null

&& request.auth.email_verified

&& request.auth.email.endsWith('@example.com')

}

}

```

### Allow only verified emails

Requires users to verify ownership of the email address before using it to read or write data. This snippet should be placed inside your `match /databases/{database}/documents` block.

```firestore

// Allow access based on email domain

match /some_collection/{document} {

allow read: if request.auth != null

&& request.auth.email_verified

&& request.auth.email.endsWith('@example.com');

}

gemini-code-assist · 2026-01-09T17:33:16Z

skills/firestore-basics/references/web_sdk_usage.md

+import { initializeApp } from "firebase/app";
+import { getFirestore } from "firebase/firestore";
+
+const firebaseConfig = {
+  // Your config options. Get the values by running 'firebase apps:sdkconfig <platform> <app-id>'
+};
+
+const app = initializeApp(firebaseConfig);
+const db = getFirestore(app);
+
+```


The markdown formatting in this section is broken. The import statements are outside the code block, and there is a stray ``` at the end. This makes the example incorrect and hard to read. All code, including imports, should be inside a single javascript code block. Additionally, this guide is missing an example for connecting to the Firestore emulator, which is present in the Android and iOS guides. This formatting issue is repeated for all code examples in this file.

Suggested change

import { initializeApp } from "firebase/app";

import { getFirestore } from "firebase/firestore";

const firebaseConfig = {

// Your config options. Get the values by running 'firebase apps:sdkconfig <platform> <app-id>'

};

const app = initializeApp(firebaseConfig);

const db = getFirestore(app);

```

import { initializeApp } from "firebase/app";

import { getFirestore, connectFirestoreEmulator } from "firebase/firestore";

const firebaseConfig = {

// Your config options. Get the values by running 'firebase apps:sdkconfig <platform> <app-id>'

};

const app = initializeApp(firebaseConfig);

const db = getFirestore(app);

// Connect to Emulator. This should be conditional (e.g. in a development environment).

connectFirestoreEmulator(db, 'localhost', 8080);

gemini-code-assist · 2026-01-09T17:33:16Z

skills/firestore-basics/references/android_sdk_usage.md

+
+// Merge
+db.collection("cities").document("LA")
+    .set(mapOf("population" to 3900000), SetOptions.merge())


The SetOptions.merge() call will fail without the required import. Please add import com.google.firebase.firestore.SetOptions to the imports section at the top of the file to make this code snippet runnable.

gemini-code-assist · 2026-01-09T17:33:16Z

skills/firestore-basics/references/android_sdk_usage.md

+    val snapshot = transaction.get(sfDocRef)
+
+    // Note: You can also use FieldValue.increment() for simple counters
+    val newPopulation = snapshot.getDouble("population")!! + 1


Using the not-null assertion operator (!!) is risky as it can cause a NullPointerException if the "population" field is missing or not a Double, which would crash the app. It's safer to handle this potential null case gracefully, for example by using the elvis operator ?: with a default value.

Suggested change

val newPopulation = snapshot.getDouble("population")!! + 1

val newPopulation = (snapshot.getDouble("population") ?: 0.0) + 1

gemini-code-assist · 2026-01-09T17:33:17Z

skills/firestore-basics/references/ios_sdk_usage.md

+    if let err = err {
+        print("Error adding document: \(err)")
+    } else {
+        print("Document added with ID: \(ref!.documentID)")


Force-unwrapping ref! with ! can lead to a runtime crash if ref is nil for any reason. It's safer to use optional chaining ? or optional binding if let.

Suggested change

print("Document added with ID: \(ref!.documentID)")

print("Document added with ID: \(ref?.documentID ?? "N/A")")

gemini-code-assist · 2026-01-09T17:33:17Z

skills/firestore-basics/references/ios_sdk_usage.md

+        let dataDescription = document.data().map(String.init(describing:)) ?? "nil"
+        print("Document data: \(dataDescription)")


Using String(describing:) on the document.data() dictionary is not very illustrative for developers. It would be more helpful to show an example of how to access individual fields from the data dictionary, for instance, by casting a value to its expected type.

Example:

if let data = document.data() { let name = data["name"] as? String ?? "N/A" print("City name: \(name)") }

gemini-code-assist · 2026-01-09T17:33:17Z

skills/firestore-basics/references/ios_sdk_usage.md

+    if let err = err {
+        print("Error getting documents: \(err)")
+    } else {
+        for document in querySnapshot!.documents {


Force-unwrapping querySnapshot! is unsafe. If an error occurs that is not caught by if let err = err, but querySnapshot is still nil, this will cause a crash. It's safer to use optional binding or the nil-coalescing operator.

Suggested change

for document in querySnapshot!.documents {

for document in querySnapshot?.documents ?? [] {

gemini-code-assist · 2026-01-09T17:33:17Z

skills/firestore-basics/references/provisioning.md

+## Deploy rules and indexes
+To deploy all rules and indexes
+```
+firebase deploy --only firestore
+```
+To deploy just rules
+```
+firebase deploy --only firestore:rules
+```
+To deploy just indexes
+```
+firebase deploy --only firestore:indexes
+```


The deployment commands are currently formatted as separate lines of inline code, which is hard to read and copy. It would be better to group them into a single bash code block for clarity and ease of use.

Suggested change

## Deploy rules and indexes

To deploy all rules and indexes

```

firebase deploy --only firestore

```

To deploy just rules

```

firebase deploy --only firestore:rules

```

To deploy just indexes

```

firebase deploy --only firestore:indexes

```

## Deploy rules and indexes

To deploy all rules and indexes:

```bash

firebase deploy --only firestore

To deploy just rules:

firebase deploy --only firestore:rules

To deploy just indexes:

firebase deploy --only firestore:indexes

gemini-code-assist · 2026-01-09T17:33:17Z

skills/firestore-basics/references/web_sdk_usage.md

+  await runTransaction(db, async (transaction) => {
+    const sfDoc = await transaction.get(sfDocRef);
+    if (!sfDoc.exists()) {
+      throw "Document does not exist!";


It's better practice to throw Error objects instead of string literals. Error objects capture stack traces and can be more easily distinguished from other thrown values, which improves debugging.

Suggested change

throw "Document does not exist!";

throw new Error("Document does not exist!");

First draft of firestore-basics skill

1890f07

gemini-code-assist bot reviewed Jan 8, 2026

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joehan added 4 commits January 8, 2026 10:44

Merge remote-tracking branch 'origin/main' into jh-skills

fc43ff9

Second pass, with more detail

869d13f

More skill improvements

1535b51

Merge branch 'main' into jh-skills

2a821b6

joehan marked this pull request as ready for review January 9, 2026 17:30

gemini-code-assist bot reviewed Jan 9, 2026

View reviewed changes

joehan added 2 commits January 9, 2026 09:37

Omit skills from prettier

c5937b4

PR fixes

766970a

	.orderBy("name", Query.Direction.KEY_ASCENDING)
	.orderBy("name", Query.Direction.ASCENDING)

	val newPopulation = snapshot.getDouble("population")!! + 1
	val newPopulation = (snapshot.getDouble("population") ?: 0.0) + 1

	print("Document added with ID: \(ref!.documentID)")
	print("Document added with ID: \(ref?.documentID ?? "N/A")")

		let dataDescription = document.data().map(String.init(describing:)) ?? "nil"
		print("Document data: \(dataDescription)")

	for document in querySnapshot!.documents {
	for document in querySnapshot?.documents ?? [] {

	throw "Document does not exist!";
	throw new Error("Document does not exist!");

First draft of firestore-basics skill #9719

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First draft of firestore-basics skill #9719

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joehan commented Jan 8, 2026 •

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