Don't launch your app without these 20 tools
Launch without these and you find out your app is broken when a user emails you, or you never find out. They go from must-haves to depends on your app, and you can start all of them for free; Stripe only takes a fee on each payment. Free plans were checked on each tool's website on November 5, 2026.
If you only have time for three, in this order: Sentry, to hear about errors; UptimeRobot, to know when it goes down; and Search Console, so Google finds it. And if you add Analytics or collect emails, CookieYes and iubenda stop being optional in the EU.
S tier: must-haves
- 001
Google Search Console
Shows how Google sees your site: which searches bring you visits, where you rank and which pages it can't index. Completely free, with 16 months of data.
search.google.com/search-console - 002
Google Analytics
Counts how many people visit, where they come from (Google, Instagram, a link) and what they do on your site. Free, and standard reports don't expire; user-level detail, used by funnels, is kept for 2 or 14 months. It uses cookies, so it needs the banner. If you want something cookieless, Umami is free up to 100,000 events a month on one site; Plausible has no free plan, only a 30-day trial.
analytics.google.com - 003
Sentry
Alerts you when your app breaks for a user, with the exact error and line of code. The free plan is for 1 person: 5,000 errors, 50 session replays, 1 uptime monitor, 1 cron monitor and 30 days of history. Alerts come by email only, and a single error repeating in a loop can burn through the month's 5,000 in a day. Turn on the built-in filters (localhost, browser extensions, bots) so you don't spend them on noise.
sentry.io - 004
PostHog
Records your users' sessions so you see where they click, where they get stuck and which screen they leave on. It also has product analytics, feature flags and surveys. Free every month: 1 million events, 5,000 replays and 1,500 survey responses, with unlimited teammates and a year of events (replays last 30 days). It's a single project, so testing and production share the allowance. It stops at the limit, so there are no surprise charges.
posthog.com - 005
UptimeRobot
Checks that your site loads and alerts you if it goes down. Free: 50 monitors checking every 5 minutes, a status page and 3 months of history. It alerts by email and up to 5 integrations; SMS and calls are paid. Commercial projects are allowed: many articles say otherwise because they restricted it in December 2024, but their current terms allow it again.
uptimerobot.com - 006
CookieYes
The cookie banner, which you need in the EU as soon as you add Analytics or an ad pixel, plus a log of who consented. Free up to 5,000 pageviews a month on one domain, with Google Consent Mode v2. The banner carries their branding and you can't change its colours. Set it up the way Spain's data protection agency (AEPD) asks: a reject-all button as visible as accept, no pre-ticked boxes, and Analytics, Clarity and the pixels blocked until the visitor accepts.
cookieyes.com - 007
iubenda
Generates your privacy policy and cookie policy, which Spanish law requires as soon as you collect an email or set cookies. Free: both policies in one language (Spanish works), with up to 3 services (say Analytics, Stripe and Resend) and their branding. Keep CookieYes for the banner, since iubenda's switches off at 5,000 pageviews. It doesn't write the legal notice (aviso legal): that's a page you write yourself with your name, tax ID, address and email.
iubenda.com/es
A tier: highly recommended
- 008
PageSpeed Insights
Measures how long your site takes to load on mobile and desktop and tells you what slows it down, like oversized images or render-blocking scripts. It's by Google, free and needs no install: paste the URL and you're done. You pass if the main content loads in 2.5 seconds or less (LCP), the page responds to a tap in 200 ms or less (INP) and nothing jumps while loading (CLS of 0.1 or less).
pagespeed.web.dev - 009
Microsoft Clarity
Heatmaps and session recordings, free forever with no traffic limits. It records up to 100,000 sessions a day per project and keeps them 30 days. Since October 31, 2025, it needs cookie consent for European visitors: without it, every page counts as a new visit. The usual split is Clarity on the public site and PostHog inside the app; if you already record sessions with PostHog, you don't need Clarity.
clarity.microsoft.com - 010
Tally
Forms and surveys you build as if you were writing a doc: waitlists, contact, feedback. Free: unlimited forms and responses, conditional logic, payments, webhooks and Notion or Google Sheets integrations. Forms carry their branding, uploads are capped at 10 MB per file, and «unlimited» means fair use: consistently over 50,000 responses a month and they'll get in touch.
tally.so - 011
Resend
Sends your app's automatic emails: welcome, password reset, receipts. Free: 3,000 emails a month and 3 domains, but capped at 100 a day, which is the limit that bites on launch day if lots of people sign up. Before your first send, add the SPF, DKIM and DMARC records it gives you to your domain's DNS: without them, Gmail can send your emails to spam or reject them.
resend.com - 012
Cloudflare
Sits in front of your site so it loads faster and to stop attacks. The free plan includes DNS, an HTTPS certificate, a CDN, unmetered DDoS protection and a firewall with basic rules. If your app is on Vercel, use it for DNS only (the grey cloud): Vercel already handles HTTPS and the CDN, and with Cloudflare's proxy in front you can get redirect loops and a cache that isn't cleared on deploy.
cloudflare.com - 013
Bing Webmaster Tools
Bing's Search Console. Its index powers Copilot, and Microsoft says it feeds ChatGPT too (also allow OAI-SearchBot in your robots.txt). You import your site and sitemaps from Search Console in one click, and IndexNow announces each new page to Bing, Yandex, Naver, Seznam and Yep at once; Google isn't one of them. There are no paid plans.
bing.com/webmasters
B tier: depends on your app
- 014
Stripe
If you charge money, it moves to S tier. Card payments and subscriptions. No monthly fee: you pay per charge, 1.5% + €0.25 on standard European cards, 2.8% + €0.25 on premium ones and 3.15% + €0.25 on non-European cards. If you sell a digital product across the EU and don't want to deal with each country's VAT, Stripe Managed Payments handles it for an extra 3.5% per sale. Stripe takes the payment, but you issue the invoice from your own invoicing software.
stripe.com/es - 015
Meta Pixel
Tells Meta who bought or signed up after seeing your Instagram or Facebook ad, so it shows the ad to similar people. You only need it if you run ads, and it costs nothing. Meta recommends pairing it with the Conversions API, which sends the same events from your server.
facebook.com/business/tools/meta-pixel - 016
Google Tag Manager
Only worth it once you have three or more tools to add, or if you run ads. It's a dashboard where you add Analytics, pixels and any other tracking code without touching your app. You paste it once and add everything else from there. Free. If you use it, remove Analytics from your code: with both, every visit counts twice.
tagmanager.google.com - 017
Crisp
A chat bubble so visitors can message you, with a shared inbox and mobile apps. Free forever for 2 teammates, with up to 100 customer profiles, which is the limit you'll actually hit.
crisp.chat - 018
Cal.com
A page where people book a call in your free slots, like Calendly. Free for 1 person, with unlimited links and calendars and payments through Stripe or PayPal. Their branding can't be removed on the free plan.
cal.com - 019
Brevo
Newsletters and marketing emails to your user list. Free: up to 100,000 contacts and 300 emails a day (newsletters and automatic emails combined), with a «Sent with Brevo» footer on every send. You can only send once Brevo approves your account.
brevo.com - 020
Ahrefs Webmaster Tools
An SEO audit of your site and the list of who links to you. Free on sites you verify you own: 5,000 pages audited a month per project and up to 1,000 backlinks and 1,000 keywords shown.
ahrefs.com/webmaster-tools
Before launch, trigger an error on purpose and take the site down for a minute: if the Sentry and UptimeRobot alerts don't reach you, they aren't set up right. And check that your database is backed up before the first user signs up.