UK SaaS observability stack 2026: Sentry vs PostHog (and what to do if you're on Highlight)

Observability used to mean three separate bills: errors, session replay, analytics. In 2026, two tools cover almost the entire ground for a UK SaaS - and a third (Highlight) just got swallowed.

This is the UK indie hacker's decision: Sentry, PostHog, or both. With GBP pricing, UK GDPR / DUA Act 2025 data residency, and the migration story for anyone still on Highlight in April 2026.

TL;DR

• PostHog if you want errors + session replay + product analytics + feature flags + surveys on one bill. Best free tier in the category.
• Sentry if you need best-in-class error triage, distributed tracing, and you already split analytics elsewhere.
• Sentry + PostHog hybrid is the pattern most UK SaaS land on past first 1,000 users: Sentry for errors, PostHog for replay + analytics + flags.
• Highlight users - LaunchDarkly acquired Highlight and the product is now LaunchDarkly Observability. If you want the original Highlight DX as a standalone, evaluate PostHog or Sentry now. Don't sit on a deprecating product.

The Highlight migration - what actually changed

If you're a UK indie who picked Highlight in 2024 or 2025 because it was the cheap Sentry-plus-replay alternative, the world shifted under you. Highlight was acquired by LaunchDarkly and the standalone product is being folded into LaunchDarkly Observability.

What that means in practice:

1. Pricing changed. LaunchDarkly's pricing model is feature-flag-first. Observability is bundled, but billing is no longer the simple per-event Highlight tiers UK indies signed up for.
2. DX shift. The product is being repositioned for teams that want flags + observability together. If you don't use LaunchDarkly for flags, the value proposition is weaker.
3. Migration window is real. Don't wait until your contract auto-renews - evaluate now while you have control.

For most UK indies on Highlight, PostHog is the closest direct replacement (one tool, errors + replay + analytics, generous free tier). For teams that want best-in-class error triage and don't mind splitting bills, Sentry + something for replay wins.

GBP pricing breakdown (April 2026)

Both providers price in USD. UK indies pay roughly USD x 0.79 (April 2026 rate, plus card FX fee).

PostHog - one bill, multiple products

Tier	What you get	Approx GBP/mo
Free	1M events/mo product analytics, 100k errors/mo, 5k session recordings/mo, 1M feature flag requests, surveys	£0
Pay-as-you-go	All free, then per-event/per-recording metering	£0 to £40 typical UK indie
Scale	Volume discounts kick in around 1M+ events	£80+

For a UK SaaS at 100 paying users, PostHog typically costs £0-£15/mo because most usage stays under free tier limits.

Sentry - error tracking-led

Tier	What you get	Approx GBP/mo
Developer	5k errors, 10k performance units, 50 replays	£0
Team	50k errors, 100k performance, 500 replays, alert rules	£20
Business	250k+ errors, distributed tracing, advanced alerts, SSO	£64+

Sentry's free tier is tighter than PostHog's on errors (5k vs 100k) but the error-triage UI and source-map support is best-in-class. If you need only error tracking and you're a single-founder UK SaaS, you'll likely sit on Developer (free) for the first 6 months.

The hybrid - both bills

Sentry Team (£20) + PostHog Free = £20/mo for top-tier error triage AND full session replay + flags + analytics. This is the pattern most UK SaaS land on by 1,000 users.

UK data residency - DUA Act 2025 and UK GDPR Chapter V

This is the bit none of the global comparisons cover. For UK SaaS, where session replay data lands matters.

What gets transferred

• Errors - stack traces, context (user agent, URL, user ID if you set one)
• Session replay - DOM snapshots, mouse moves, network events, console logs (potentially PII unless masked)
• Performance - URL, timings, custom tags

Replay is the heavy one. If you record an authenticated UK user typing into a form, you're capturing personal data subject to UK GDPR.

Where each tool stores data (April 2026)

Tool	EU/UK option	US default	Notes
Sentry	EU (Frankfurt) - paid plans	US (default)	Set via project settings, must opt in
PostHog	EU Cloud (Frankfurt)	US Cloud	Choose at signup, can't switch later without reset
LaunchDarkly Observability	US-first	--	EU options are tier-gated

What this means for UK SaaS

• Pick the EU instance at signup. UK <-> EU transfers under the EU adequacy decision are legally simple. UK <-> US transfers require IDTA / UK addendum to SCCs and a transfer impact assessment.
• Mask PII in replay. Both Sentry and PostHog support masking by CSS selector (.password-input, [data-private]). Configure this before you ship.
• Update your sub-processor list. Both Sentry and PostHog must appear in your privacy policy + sub-processor table (see our UK SaaS legal pages template).

The DUA Act 2025 changes the cookie consent picture (analytics-only first-party cookies are now exempt) but does not change cross-border transfer rules. You still need IDTA cover for US replay storage.

DX comparison - the boring stuff that matters

Error grouping

• Sentry - the gold standard. Source maps work first time, stack-trace fingerprinting groups duplicates correctly, integrations with GitHub, Linear, Jira are mature.
• PostHog - good, but newer. Source map upload requires a manual step in CI. Grouping is decent but you'll occasionally see what should be one error split across three issues.

If you're shipping a Next.js app on Vercel, both have a near-zero-config integration. Sentry has the edge on auto-source-maps via @sentry/nextjs.

Session replay quality

• PostHog - replay is a flagship product. Network requests, console logs, DOM, scroll position, all rolled up. Auto-capture means you don't have to tag events.
• Sentry - replay is solid but Sentry-style: errors first, replay as a back-pointer when an error fires. Less useful for product UX investigation.

Distributed tracing

• Sentry - mature. If you have a Next.js app calling a Hono API on a Hetzner sidecar (see our Vercel + VPS sidecar guide), Sentry will stitch the traces.
• PostHog - tracing is in beta. For complex backends you'll want Sentry.

Time to first useful signal

• Sentry - 15 minutes from signup to first error captured in a Next.js app.
• PostHog - 20 minutes (auto-capture is great but you'll spend time configuring masks).

Decision matrix by stage

Pre-revenue (0 paying users)

Pick PostHog. One free product covers errors, replay, analytics, and flags. You will not exceed the free tier. Optimise for fewer dashboards, not best-in-class error triage.

If you must have Sentry-quality errors from day one (e.g., you ship complex backend logic), use Sentry Developer (free) for errors only and skip replay until you have users.

First 100 paying users

Pick PostHog OR Sentry + PostHog hybrid. At this stage you're still on free tiers for both. Decision driver: do you spend more time triaging errors or understanding user behaviour?

• More time on errors -> Sentry Team (£20) + PostHog Free for replay/analytics
• More time on UX/product -> PostHog only

First 1,000 paying users

Almost always the hybrid. Sentry Team (£20) + PostHog Pay-as-you-go (£20-£40 for typical UK SaaS at this scale) = £40-£60/mo. Worth every penny.

10,000+ users

You're past the indie hacker threshold and need to think about cost optimisation, sampling, and possibly self-hosting (PostHog has a self-host option, Sentry has both). At this point hire someone to think about observability properly.

The Sentry + PostHog hybrid - concrete wiring

Most mature UK SaaS land here. The setup is two SDKs, ten lines each.

Next.js 16 + Vercel + Sentry

npm install @sentry/nextjs
npx @sentry/wizard@latest -i nextjs

That generates sentry.client.config.ts, sentry.server.config.ts, and a Webpack plugin for source maps. Set SENTRY_DSN in Vercel env. Done.

Next.js 16 + Vercel + PostHog

npm install posthog-js posthog-node

// app/providers.tsx
'use client'
import posthog from 'posthog-js'
import { PostHogProvider } from 'posthog-js/react'
import { useEffect } from 'react'

if (typeof window !== 'undefined') {
  posthog.init(process.env.NEXT_PUBLIC_POSTHOG_KEY!, {
    api_host: 'https://eu.i.posthog.com', // EU residency
    person_profiles: 'identified_only',
    capture_pageview: false, // we'll do this manually for App Router
    session_recording: {
      maskAllInputs: true,
      maskTextSelector: '.private', // mask anything with class="private"
    },
  })
}

export function Providers({ children }: { children: React.ReactNode }) {
  return <PostHogProvider client={posthog}>{children}</PostHogProvider>
}

Wrap <Providers> in app/layout.tsx. Set NEXT_PUBLIC_POSTHOG_KEY in Vercel env.

Cross-tool linking

In sentry.client.config.ts, add:

import * as Sentry from '@sentry/nextjs'
import posthog from 'posthog-js'

Sentry.init({
  dsn: process.env.NEXT_PUBLIC_SENTRY_DSN,
  beforeSend(event) {
    const sessionId = posthog.get_session_id?.()
    if (sessionId) {
      event.extra = { ...event.extra, posthog_session: sessionId }
    }
    return event
  },
})

Now every Sentry error has a clickable link back to the PostHog session replay. This is the killer feature of the hybrid - error in Sentry, replay in PostHog, one click.

Five UK SaaS observability failure modes

1. Picking the US instance because the signup flow defaults to it. UK <-> US transfers need IDTA cover. Pick EU at signup. Both Sentry and PostHog have EU clouds, you just have to choose them.
2. Recording PII in replay. Forms, internal tooling, password managers - all leak. Mask aggressively. Test in staging by recording your own session and watching the replay.
3. Forgetting to upload source maps. Stack traces in Sentry without source maps are useless. The wizard sets up CI; verify after your first production deploy.
4. Alert fatigue. Both tools will spam Slack on day one. Set a rate-limit (max 1 alert per error per hour) and ignore non-actionable issues for the first week to find your real signal.
5. Not putting either tool in your privacy policy. UK GDPR requires you to list third-party data processors. Sentry and PostHog both qualify. Update before you go live (template at our UK SaaS legal pages guide).

30-minute ship-it - PostHog only

Best for pre-revenue UK indies.

1. Sign up at posthog.com, pick EU Cloud.
2. Create a project, copy the project key.
3. npm install posthog-js posthog-node.
4. Add the provider snippet above to app/providers.tsx.
5. Set NEXT_PUBLIC_POSTHOG_KEY and NEXT_PUBLIC_POSTHOG_HOST=https://eu.i.posthog.com in Vercel env.
6. Deploy. Visit your live site, do some clicks.
7. Confirm the session replay shows up under PostHog -> Recordings within 1-2 minutes.
8. Add a privacy mask to any auth form: <input className="ph-no-capture" />.
9. Update your privacy policy sub-processors table.
10. Set one error alert and one product analytics dashboard.

30-minute ship-it - Sentry + PostHog hybrid

Best for UK SaaS with paying users.

1. Sign up for both. Pick EU instances on both.
2. Run the Sentry wizard (npx @sentry/wizard@latest -i nextjs).
3. Add the PostHog provider as above.
4. Add the Sentry-PostHog session linking snippet.
5. Configure source map upload in CI (Sentry wizard does this automatically for Vercel).
6. Mask PII selectors in PostHog replay config.
7. Set Sentry alert rules (error rate > 5/min, new issue type).
8. Set PostHog event funnels for your three core conversions (signup, activation, paid).
9. Update your privacy policy with both processors.
10. Ship a test error in production. Click through Sentry -> PostHog. Verify the replay loads.

Frequently asked questions

Is Highlight dead for UK indies?

Standalone Highlight is being absorbed into LaunchDarkly Observability. If you don't use LaunchDarkly for feature flags, the product no longer fits the UK indie hacker brief. Migrate to PostHog (closest direct replacement) or Sentry + PostHog hybrid before your next renewal cycle.

Can I self-host PostHog or Sentry to keep data in the UK?

Both support self-hosting. PostHog has a Helm chart and a Docker Compose option. Sentry self-hosting is more involved (Kafka, Postgres, Redis, ClickHouse). For UK SaaS under 100k users, self-hosting costs more in operational time than the £40-£60/mo hybrid bill saves you. Revisit at 10k+ users or in regulated sectors (financial services, health).

What about Datadog, New Relic, or Better Stack?

Datadog and New Relic are enterprise-priced. Better Stack is genuinely competitive on logging and uptime monitoring but doesn't compete with PostHog on replay or product analytics. For a UK indie hacker SaaS, the Sentry + PostHog hybrid covers more ground for less money.

Does DUA Act 2025 mean I don't need a cookie banner for PostHog?

Partially. DUA Act 2025 exempts first-party analytics-only cookies from consent. PostHog's session recording is borderline - it's first-party (proxied through your domain) but it captures interactions, not just page views. Conservative reading: keep consent for replay, drop the banner for analytics-only events. See our DUA Act cookie exemption walkthrough for the decision tree.

Can I run Sentry and PostHog without slowing down my Next.js app?

Yes. Both ship lazy-loaded clients (~25KB and ~40KB gzipped respectively). Use posthog.init({ disable_session_recording: true }) until a user is identified to defer the heavy replay payload. For Sentry, tracesSampleRate: 0.1 keeps the perf overhead under 1% on most pages.

Key takeaways

1. PostHog is the closest direct replacement for Highlight - one bill, errors + replay + analytics + flags, generous free tier.
2. Sentry remains best-in-class for error triage and distributed tracing - pair it with PostHog for full coverage.
3. The Sentry + PostHog hybrid at GBP 40-60/mo is the standard pattern for UK SaaS past 1,000 users.
4. Pick EU Cloud on both at signup to avoid UK GDPR Chapter V transfer headaches under DUA Act 2025.
5. Mask PII in session replay, upload source maps in CI, and list both processors in your privacy policy before going live.

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