Quick answer: Uncapped Poetics tomestones — which most veterans have thousands of — buy items you can resell on the market board. Capped tomestones are usually better spent on gear, but converting them to sellable materials is worth it when the gil price beats the gear value. Check current exchange rates against live prices to find the best conversion.
Tomestones are the currency you earn whether you want them or not. Roulettes pay them, so does every dungeon and raid you run for other reasons, and for most players they pile up with nothing left to buy. A good chunk of what they purchase is tradeable — which makes tomestones a gil faucet that costs you nothing extra to run.
Poetics are uncapped. There's no weekly limit, they accumulate forever, and long-time players tend to be sitting on a mountain of them with every relevant reward already bought. Anything you convert is pure profit on a currency you had no other use for. Poetics buy the widest range of marketable goods by far — 87 tradeable items in our exchange data.
Capped tomestones are weekly-limited. You get a fixed allowance per week, so every stone you spend on gil is a stone not spent on gearing. Here the question isn't "is this profitable" but "is this the best use of a scarce weekly resource" — and the answer is usually no until you're geared. The current capped tome buys a much narrower list: 18 tradeable items, almost all current-tier crafting materials.
The tradeable Poetics stock falls into four rough groups:
Current-tier tomestones are simpler: they buy the crafting materials of the moment, which sell quickly while the tier is live and decay in value once the next patch lands.
That's the whole ranking. Because the same item is sometimes offered at different rates by different vendors, always take the cheaper exchange — our data has several items listed at two costs, and the difference is free money.
The Tomestone Exchange tool runs that math across every tradeable exchange (117 in total, across Poetics and the current capped tome), prices them live against your world, and sorts by gil per tomestone.
Same warning as every other conversion on this site: the best gil-per-tomestone result is frequently an item with one optimistic listing and no buyers. A slightly worse rate on something that sells daily beats a spectacular rate on something that sits in your retainer until the next expansion. Check sales velocity, not just price.
There's also a timing element. Materials for the current crafting tier are worth the most early in a patch cycle, when everyone is levelling crafters and building gear. Old-expansion materials are steadier but flatter. If you're sitting on a large Poetics balance, spreading conversions over weeks gets you a better average than dumping everything into the board at once — you are, after all, competing with yourself when you list forty of the same thing.
Put this into practice with live market-board prices for your world:
Rank tomestone exchanges → Passive & AFK gil →
XIV Profitability is a free, fan-made tool. Not affiliated with Square Enix. Prices via Universalis. FINAL FANTASY XIV © SQUARE ENIX CO., LTD.