Synthiz vs Obsidian: which should you choose?

What each tool is for

Obsidian is a Markdown editor that works on a folder on your disk. Nothing leaves your machine by default: the files are yours and will still be readable in ten years with any text editor. Notes connect through internal links, and a graph view shows the structure that emerges. Around that deliberately simple core, a very active community has built thousands of plugins. Personal use is free.

Synthiz comes at the same ground from the opposite end: it does not assume the note exists, it manufactures it from a source. You hand it a link — an article, a YouTube video, a podcast, a PDF — or you subscribe to an RSS feed, a channel, a show. It syncs on its own (hourly, every six hours, or once a day), transcribes audio and video, produces a summary and extracts concepts before you even open the app. Every statement carries timestamped citations that jump back into the transcript at the exact second. A cross-source analysis surfaces agreements, tensions and blind spots across several sources, and Thoughts hold the human part: your own reflections and objections, anchored to the sources.

Obsidian is a workshop. Synthiz is a preparation line.

Comparison table

Criterion	Obsidian	Synthiz
Data storage	Local Markdown files, you own them	Hosted online service
Entry cost	Free for personal use	Free account, paid plan at €9 per month
Extensibility	Enormous, thousands of community plugins	None, closed integrated product
Interface customisation	Very deep, themes and CSS	Limited
Audio and video transcription	Via external plugin and API key	Native
Automatic summary and concepts	Via external plugin	Native, as soon as the source lands
Feed monitoring via RSS and channels	Via plugin	Native, with automatic processing
Timestamped citations into the transcript	No	Yes
Search	Lexical: you must remember the words you wrote	Hybrid, semantic and lexical fused
Browser extension	Third-party web-clipping plugins	One-click capture and search of your own base from the page
Tracing an idea back to its source	Depends on your links and your discipline	Timestamped citation, back into the transcript
Links between notes	Manual, with graph view	Concepts linked automatically
Longevity if the service dies	Total, they are your files	Depends on the service
Setup effort	High up front	None

When to choose Obsidian

Obsidian beats Synthiz on several counts, and they are not minor ones.

Local-first, first of all. No vendor can shut the service down, change its terms or lose your data: the worst case leaves you with a folder of perfectly readable text. For research conducted over ten years, or for anyone who refuses on principle to hand a knowledge base to a third party, that is a decisive argument Synthiz cannot match.

Then the free tier. Personal use costs nothing, indefinitely: only official sync and publishing are paid, and a folder you sync yourself replaces both.

Finally, extensibility. The ecosystem covers practically everything: Dataview to query your notes like a database, Templater for automation, Spaced Repetition for memorisation, Excalidraw for diagrams. If your need is specific and slightly eccentric, there is probably a plugin — and if not, you can write it. Synthiz does not open up that way, and Obsidian is also a far better tool for long-form writing.

When to choose Synthiz

Obsidian, the Zettelkasten and second-brain methods in general are excellent for thinking and connecting ideas. Their weak point lies elsewhere: retrieval. Six months after noting an idea, finding exactly where it came from assumes either that you were disciplined about your links, or that you remember the words you used at the time.

That is the crux of the problem, and it is technical. Obsidian's search is lexical: it matches character strings. If your note says 'the side effects of sales bonuses' and you search for 'perverse incentives', nothing comes back — not because the note is missing, but because your vocabulary shifted between writing and searching.

Synthiz fuses two signals, a semantic search over embeddings and a full-text lexical search, and decides relevance not with a fixed similarity threshold but by how far a document sits from the distribution of its own query. The difference is measurable: on a production corpus of 948 embeddings, the query 'feudalism' — five genuinely relevant documents — and a query matching nothing at all peaked just 0.09 apart. A fixed 0.65 threshold returned nothing to a user who did own those five sources; lowering it far enough to reach them let anything back in. The benefit is twofold: you find things without recalling the exact words, and a search with no match honestly answers zero results instead of noise. On top of that comes traceability, with timestamped citations pointing at the exact passage of the transcript, where a copied note only preserves the approximation of the copy.

That search is also available from the Chrome extension, which changes when it becomes useful: the panel shows the excerpt around the term you searched for rather than a list of results. Halfway through a video, a claim feels familiar, you type three words and see what your own base says about it, without switching tabs. The same extension saves a page, a YouTube video or a podcast in one click and pulls the transcript automatically.

The last point is feeding the base. An Obsidian vault does not fill itself: you watch an hour-long talk, promise yourself you will write it up, and the note never appears. With Synthiz the material arrives already transcribed, summarised and connected, the cross-source analysis exposes tensions a hand-built graph never shows, and there is nothing to configure — no plugin, no API key, nothing to maintain when a maintainer walks away.

Verdict by profile

Developer, tinkerer, local-first believer: Obsidian. Full control and file longevity outweigh convenience.

Long-haul researcher: Obsidian for the archive and the writing, Synthiz upstream if the corpus involves a lot of audio and video to transcribe and verify.

Busy professional with heavy reading: Synthiz. Configuration and manual entry are exactly what makes knowledge bases collapse.

Vault already large and hard to query: Synthiz. Past a thousand notes the problem is no longer writing but finding, and that is where lexical search shows its limits.

Pricing moves: check each vendor's site before deciding.