Freelance blog post - PostHog vs Langfuse

[natalia-amorim]

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Comparison article for PostHog vs Langfuse (freelance submission)

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contents/blog/posthog-vs-langfuse.mdx — 3 errors, 99 warnings, 1 suggestions

Line	Severity	Message	Rule
2:20	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
14:28	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
20:124	warning	Capitalize 'Logs' for PostHog's product. Use 'logs' for the general industry concept.	PostHogBase.ProductNames
22:24	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
26:6	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
26:164	warning	Capitalize 'Experiments' for PostHog's product. Use 'experiments' for the general industry concept.	PostHogBase.ProductNames
28:146	warning	Capitalize 'Product Analytics' for PostHog's product. Use 'product analytics' for the general industry concept.	PostHogBase.ProductNames
28:187	warning	Capitalize 'Session Replay' for PostHog's product. Use 'session replay' for the general industry concept.	PostHogBase.ProductNames
28:222	warning	Capitalize 'Feature Flags' for PostHog's product. Use 'feature flags' for the general industry concept.	PostHogBase.ProductNames
28:255	warning	Capitalize 'Experiments' for PostHog's product. Use 'experiments' for the general industry concept.	PostHogBase.ProductNames
28:284	warning	Capitalize 'Error Tracking' for PostHog's product. Use 'error tracking' for the general industry concept.	PostHogBase.ProductNames
28:319	warning	Capitalize 'Surveys' for PostHog's product. Use 'surveys' for the general industry concept.	PostHogBase.ProductNames
34:316	warning	Capitalize 'Session Replay' for PostHog's product. Use 'session replay' for the general industry concept.	PostHogBase.ProductNames
40:74	warning	Capitalize 'Experiments' for PostHog's product. Use 'experiments' for the general industry concept.	PostHogBase.ProductNames
42:14	warning	Capitalize 'Experiments' for PostHog's product. Use 'experiments' for the general industry concept.	PostHogBase.ProductNames
42:276	warning	'Frequentist' is a possible misspelling.	PostHogBase.Spelling
55:4	warning	'Comparing PostHog and Langfuse' heading should be in sentence case, and product names should be capitalized.	PostHogBase.SentenceCase
55:26	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
59:63	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
83:19	warning	'Langfuse's' is a possible misspelling.	PostHogBase.Spelling
87:1	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
87:274	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
106:71	warning	Capitalize 'Workflows' for PostHog's product. Use 'workflows' for the general industry concept.	PostHogBase.ProductNames
106:173	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
110:74	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
110:124	warning	Capitalize 'Workflows' for PostHog's product. Use 'workflows' for the general industry concept.	PostHogBase.ProductNames
114:39	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
130:41	warning	Capitalize 'Experiments' for PostHog's product. Use 'experiments' for the general industry concept.	PostHogBase.ProductNames
130:91	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
151:138	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
153:268	warning	Capitalize 'Product Analytics' for PostHog's product. Use 'product analytics' for the general industry concept.	PostHogBase.ProductNames
157:32	warning	Capitalize 'Workflows' for PostHog's product. Use 'workflows' for the general industry concept.	PostHogBase.ProductNames
157:49	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
157:114	warning	Capitalize 'Product Analytics' for PostHog's product. Use 'product analytics' for the general industry concept.	PostHogBase.ProductNames
157:133	warning	Capitalize 'Session Replay' for PostHog's product. Use 'session replay' for the general industry concept.	PostHogBase.ProductNames
157:149	warning	Capitalize 'Feature Flags' for PostHog's product. Use 'feature flags' for the general industry concept.	PostHogBase.ProductNames
157:164	warning	Capitalize 'Experimentation' for PostHog's product. Use 'experimentation' for the general industry concept.	PostHogBase.ProductNames
185:30	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
187:27	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
199:4	warning	'When to choose PostHog vs Langfuse' heading should be in sentence case, and product names should be capitalized.	PostHogBase.SentenceCase
199:30	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
207:84	warning	Capitalize 'Error Tracking' for PostHog's product. Use 'error tracking' for the general industry concept.	PostHogBase.ProductNames
208:42	warning	Capitalize 'Session Replay' for PostHog's product. Use 'session replay' for the general industry concept.	PostHogBase.ProductNames
208:58	warning	Capitalize 'Experiments' for PostHog's product. Use 'experiments' for the general industry concept.	PostHogBase.ProductNames
210:5	warning	'Choose Langfuse for AI observability if:' heading should be in sentence case, and product names should be capitalized.	PostHogBase.SentenceCase
210:12	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
213:83	warning	Capitalize 'Experiments' for PostHog's product. Use 'experiments' for the general industry concept.	PostHogBase.ProductNames
214:80	warning	Capitalize 'Workflows' for PostHog's product. Use 'workflows' for the general industry concept.	PostHogBase.ProductNames
214:138	warning	Capitalize 'Experiments' for PostHog's product. Use 'experiments' for the general industry concept.	PostHogBase.ProductNames
223:37	warning	Capitalize 'Session Replay' for PostHog's product. Use 'session replay' for the general industry concept.	PostHogBase.ProductNames
223:53	warning	Capitalize 'Feature Flags' for PostHog's product. Use 'feature flags' for the general industry concept.	PostHogBase.ProductNames
223:72	warning	Capitalize 'Error Tracking' for PostHog's product. Use 'error tracking' for the general industry concept.	PostHogBase.ProductNames
223:297	warning	Capitalize 'Experiments' for PostHog's product. Use 'experiments' for the general industry concept.	PostHogBase.ProductNames
227:5	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
227:133	warning	'Langfuse's' is a possible misspelling.	PostHogBase.Spelling
231:128	error	Hi, Andy here... use an en dash ( – ) with spaces. On Mac, holding down the Option and hyphen key will give you an en dash.	PostHogBase.EnDash
231:180	warning	Capitalize 'Experiments' for PostHog's product. Use 'experiments' for the general industry concept.	PostHogBase.ProductNames
233:33	warning	'LLMOps' is a possible misspelling.	PostHogBase.Spelling
235:16	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
240:57	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
242:3	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
242:239	warning	Capitalize 'Product Analytics' for PostHog's product. Use 'product analytics' for the general industry concept.	PostHogBase.ProductNames
242:280	warning	Capitalize 'Session Replay' for PostHog's product. Use 'session replay' for the general industry concept.	PostHogBase.ProductNames
242:315	warning	Capitalize 'Feature Flags' for PostHog's product. Use 'feature flags' for the general industry concept.	PostHogBase.ProductNames
242:348	warning	Capitalize 'Experiments' for PostHog's product. Use 'experiments' for the general industry concept.	PostHogBase.ProductNames
242:377	warning	Capitalize 'Error Tracking' for PostHog's product. Use 'error tracking' for the general industry concept.	PostHogBase.ProductNames
244:49	error	Hi, Andy here... use an en dash ( – ) with spaces. On Mac, holding down the Option and hyphen key will give you an en dash.	PostHogBase.EnDash
244:81	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
244:118	warning	Capitalize 'Workflows' for PostHog's product. Use 'workflows' for the general industry concept.	PostHogBase.ProductNames
249:24	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
251:138	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
258:30	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
260:181	warning	Capitalize 'Product Analytics' for PostHog's product. Use 'product analytics' for the general industry concept.	PostHogBase.ProductNames
260:200	warning	Capitalize 'Session Replay' for PostHog's product. Use 'session replay' for the general industry concept.	PostHogBase.ProductNames
260:223	warning	Capitalize 'Error Tracking' for PostHog's product. Use 'error tracking' for the general industry concept.	PostHogBase.ProductNames
260:255	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
265:32	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
267:130	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
276:42	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
278:1	suggestion	Avoid hedging. Be opinionated instead of saying 'It depends'.	PostHogEditorial.Hedging
278:76	warning	Use the Oxford comma before 'and' or 'or' in a list of three or more items.	PostHogBase.OxfordComma
278:99	warning	'Braintrust' is a possible misspelling.	PostHogBase.Spelling
280:52	warning	Capitalize 'Product Analytics' for PostHog's product. Use 'product analytics' for the general industry concept.	PostHogBase.ProductNames
280:120	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
289:3	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
304:3	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
311:13	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
313:3	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
315:20	warning	Use 'GitHub' instead of 'github'.	Vale.Terms
315:39	warning	Use 'PostHog' instead of 'posthog'.	Vale.Terms
316:3	warning	'Langfuse's' is a possible misspelling.	PostHogBase.Spelling
316:21	warning	Use 'GitHub' instead of 'github'.	Vale.Terms
321:37	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
323:16	warning	'Langfuse's' is a possible misspelling.	PostHogBase.Spelling
330:286	warning	'Langfuse's' is a possible misspelling.	PostHogBase.Spelling
332:263	warning	'Langfuse' is a possible misspelling.	PostHogBase.Spelling
339:78	warning	'Langfuse's' is a possible misspelling.	PostHogBase.Spelling
344:17	warning	Capitalize 'Session Replay' for PostHog's product. Use 'session replay' for the general industry concept.	PostHogBase.ProductNames
346:1	warning	Capitalize 'Session Replay' for PostHog's product. Use 'Session replay' for the general industry concept.	PostHogBase.ProductNames
346:218	warning	Capitalize 'Logs' for PostHog's product. Use 'logs' for the general industry concept.	PostHogBase.ProductNames
351:17	warning	Capitalize 'Feature Flags' for PostHog's product. Use 'feature flags' for the general industry concept.	PostHogBase.ProductNames
353:1	warning	Capitalize 'Feature Flags' for PostHog's product. Use 'Feature flags' for the general industry concept.	PostHogBase.ProductNames
353:220	error	Hi, Andy here... use an en dash ( – ) with spaces. On Mac, holding down the Option and hyphen key will give you an en dash.	PostHogBase.EnDash

[github-actions]

Bundle report

Total JS (gzip)

6.29 MiB (+1.4 KiB / +0.0%)

Largest changed named chunks

Chunk	Gzip	Δ vs master
app.js	1981.5 KiB	+1.4 KiB / +0.1%

Eager graph (static-import closure per entrypoint)

Entrypoint	Eager size	Budget	Modules
✅ app	24.23 MiB (+5.7 KiB / +0.0%)	report-only	5516

Largest modules in the app closure

Module	Size
css ./node_modules/.pnpm/css-loader@5.2.7_webpack@5.101.3/node_modules/css-loader/dist/cjs.js??ruleSet[1].rules[8].oneOf[1].use[1]!./node_modules/.pnpm/postcss-loader@4.3.0_postcss@8.5.6_webpack@5.101.3/node_modules/postcss-loader/dist/cjs.js??ruleSet[1].rules[8].oneOf[1].use[2]!./src/styles/global.css	708.0 KiB
./src/components/Stickers/Stickers.tsx	696.4 KiB
./.cache/caches/gatsby-plugin-mdx/mdx-scopes-dir/31a094f140f119e73085d847ae81b99b.js + 2 modules	584.2 KiB
./node_modules/.pnpm/@radix-ui+react-icons@1.3.2_react@18.3.1/node_modules/@radix-ui/react-icons/dist/react-icons.esm.js	481.4 KiB
./node_modules/.pnpm/@codemirror+view@6.38.2/node_modules/@codemirror/view/dist/index.js	458.1 KiB
./node_modules/.pnpm/rehype-raw@7.0.0/node_modules/rehype-raw/lib/index.js + 29 modules	395.1 KiB
./node_modules/.pnpm/@posthog+icons@0.36.6_react-dom@18.3.1_react@18.3.1__react@18.3.1/node_modules/@posthog/icons/dist/posthog-icons.cjs.js	364.8 KiB
./node_modules/.pnpm/@posthog+icons@0.36.6_react-dom@18.3.1_react@18.3.1__react@18.3.1/node_modules/@posthog/icons/dist/posthog-icons.es.js	354.8 KiB
./src/hooks/useCustomers.tsx + 54 modules	353.9 KiB
./node_modules/.pnpm/react-markdown@8.0.7_@types+react@16.14.66_react@18.3.1/node_modules/react-markdown/lib/react-markdown.js + 88 modules	351.4 KiB
./node_modules/.pnpm/cloudinary-core@2.14.0_lodash@4.17.21/node_modules/cloudinary-core/cloudinary-core.js	281.9 KiB
./src/components/ProductComparisonTable/index.tsx + 116 modules	273.3 KiB
./node_modules/.pnpm/@codesandbox+sandpack-react@2.20.0_react-dom@18.3.1_react@18.3.1__react@18.3.1/node_modules/@codesandbox/sandpack-react/dist/index.mjs	266.6 KiB
./node_modules/.pnpm/d3@7.9.0/node_modules/d3/src/index.js + 208 modules	247.4 KiB
./src/components/Pricing/PricingSlider/Slider.tsx + 87 modules	239.9 KiB

---

Eager-graph budgets are report-only until a baseline is established. Sizes are gzip of public/**/*.js; eager size is webpack module source bytes.

[ivanagas]

Looking good, thanks for all your work on this one :)

[ivanagas]

Suggested change

	A real user types something you never tested, your agent takes a hard left turn, and suddenly you're scrolling through raw logs trying to reconstruct what happened.
	A real user types something you never tested, your agent takes a hard left turn, and suddenly you're scrolling through logs trying to reconstruct what happened.

[ivanagas]

overall nice though, thanks!

[ivanagas]

core pillar and day one are both cliche, so lets just have one of them

Suggested change

	Langfuse built prompt management as a core pillar from day one. However, PostHog is playing catch-up with a [Prompt Management](/docs/prompt-management) tool (currently in beta). But while it already covers versioning, runtime fetching, and A/B testing of prompt versions, Langfuse is still further along with features like labels, playground testing, and composable prompts.
	Langfuse had prompt management from day one. However, PostHog is playing catch-up with a [Prompt Management](/docs/prompt-management) tool (currently in beta). While PostHog's tool already covers versioning, runtime fetching, and A/B testing of prompt versions, Langfuse is still further along with features like labels, playground testing, and composable prompts.

[ivanagas]

I think this duplicates a lot of what's said in the sentence above. The in-depth metrics bit maybe doesn't even make sense to include here.

Suggested change

**Worth noting:** Right now, PostHog's prompt management handles core workflows like creating versioned prompts for fetching them at runtime with caching and fallback. But Langfuse still has deeper features, such as environment-based deployment labels and composable prompt chains. If you really need in-depth metrics *just for LLM* features, Langfuse is the stronger pick.

[ivanagas]

Suggested change

	Both tools score outputs with LLM-as-a-judge and custom code evaluators. Langfuse goes further into pre-deployment quality workflows: annotation queues for scoring specific parts of a trace, curated datasets, and experiment runs across them.
	Both tools can score outputs with LLM-as-a-judge and custom code evaluators. Langfuse goes further into pre-deployment quality workflows: annotation queues for scoring specific parts of a trace, curated datasets, and experiment runs across them.

[ivanagas]

Let's let people decide that themselves 😅

Suggested change

For pre-deployment quality assurance, Langfuse is the stronger pick right now.

[ivanagas]

Suggested change

	Both [PostHog](/) and [Langfuse](/blog/best-langfuse-alternatives) exist for this exact moment. They both show you [what your LLMs are actually doing](blog/what-is-ai-observability) in production – traces, token costs, latency, the works.
	Both [PostHog](/) and [Langfuse](/blog/best-langfuse-alternatives) exist for this exact moment. They both show you [what your LLMs are actually doing](/blog/what-is-ai-observability) in production – traces, token costs, latency, the works.

[ivanagas]

Suggested change

2. **PostHog** is a developer platform for building self-driving products. [AI observability](/ai-observability) is one of many tools alongside [product analytics](/product-analytics), [session replay](/session-replay), [feature flags](/feature-flags), [experiments](/experiments), [error tracking](/error-tracking), [surveys](/surveys), and more. It's built for AI-pilled teams who want discover issues wherever they exist, make improvements fast, and evaluate that they actually work.

2. **PostHog** is a developer platform for building self-driving products. [AI observability](/ai-observability) is one of many tools alongside [product analytics](/product-analytics), [session replay](/session-replay), [feature flags](/feature-flags), [experiments](/experiments), [error tracking](/error-tracking), [surveys](/surveys), and more. It's built for AI-pilled teams who want to discover issues wherever they exist, make improvements fast, and evaluate that they actually work.

[ivanagas]

Suggested change

Although both have prompt playgrounds, PostHog goes further with [prompt experiments (beta)](/docs/prompt-management/prompt-experiments) let you pit two or more versions of a prompt against each other. It splits users between them [via a feature flag](/docs/feature-flags) and reports cost, latency, eval pass rate, and usage analytics per variant, with a confidence interval against the control.

Although both have prompt playgrounds, PostHog goes further with [prompt experiments (beta)](/docs/prompt-management/prompt-experiments) that let you pit two or more versions of a prompt against each other. It splits users between them [via a feature flag](/docs/feature-flags) and reports cost, latency, eval pass rate, and usage analytics per variant, with a confidence interval against the control.

[ivanagas]

Suggested change

	Feature flags let you roll out new AI features, prompts, or model versions gradually. You can release to a small percentage of users, monitor traces and product metrics, and roll back instantly if something looks wrong — without redeploying code.
	Feature flags let you roll out new AI features, prompts, or model versions gradually. You can release to a small percentage of users, monitor traces and product metrics, and roll back instantly if something looks wrong – without redeploying code.

[ivanagas]

A good FAQ might be PostHog events vs Langfuse units.

Here's Claude:

Good question — it's the crux of why the comparison is tricky. Here's the distinction:

Langfuse units

A unit is any single record Langfuse stores, of three types:

Units = Traces + Observations + Scores

• Trace — the top-level container for one request (e.g. one chatbot turn). 1 per request.
• Observation — every step inside the trace: each LLM call (generation), each retrieval/function step (span), each event. A trace with 3 LLM calls + 2 retrieval steps = 5 observations.
• Score — an evaluation attached to a trace/observation: LLM-as-judge results, human annotations, experiment scores.

So the trace itself is billed as its own unit, plus everything in it, plus every eval you run on it. That's why one trace ≈ ~7 units in their example (1 trace + ~6 observations + a fraction of a score).

PostHog events

PostHog bills per event, and every captured item is a separate $ai_* event:

• $ai_generation — one LLM call (the primary/most common event)
• $ai_span — an operation within a trace (retrieval, function call)
• $ai_trace — the trace-level record
• $ai_embedding — a vectorization call

There's no separate "score" event type the way Langfuse has — evals in PostHog aren't billed as a distinct ingestion unit in the same way.

The practical differences

	Langfuse unit	PostHog event
Trace container	billed (1 unit)	billed ($ai_trace)
Each LLM call	billed (observation)	billed ($ai_generation)
Each span/step	billed (observation)	billed ($ai_span)
Evals / annotations	billed (score)	not a billed ingestion unit
Rate	$8 per 100k	$6 per 100k ($0.00006 each)

Bottom line: the two count instrumentation items almost identically (trace + every observation/span), so for the same app they land at roughly the same volume — which is why applying the same ~7× multiplier to both is fair. The two real divergences are:

1. Scores. If you run lots of evals/annotations, Langfuse's unit count climbs faster than PostHog's event count, because those are billable units in Langfuse but not billable events in PostHog.
2. Instrumentation depth. If you only wrap LLM calls and skip spans, both drop — but PostHog can drop further if you don't emit the trace/span wrapper events.

So "units" and "events" are conceptually the same idea (one billed record per captured thing), differing mainly in what counts as billable (Langfuse adds scores) and the per-item price ($8 vs $6 per 100k).