Build planner

Make a character, from its archetype and the Rose to its skill gems and gear, and read off its damage, defences and mana against any monster, computed by the game's own code.

The planner is the game's Path of Building: a place to try a build before you play it. Pick a level and a main skill, put an item in each slot, and the sidebar shows what that character does. A character here is everything a build is made of: its archetype and attributes, the places it has lit on the Rose, its skill gems and their supports, and its gear. The rules for all of it are in the game's simulation, but the game has no screens for the Rose and gems yet, so for now the planner is the only place to try them.

The numbers are the game's. Path of Building rewrites Path of Exile's rules in its own code and reads each item's text back into numbers, and both have to be fixed by hand every time the game changes. The planner does neither: its engine is the sim's own Rust (crates/planner, built on sim::calc and sim::items) compiled to WebAssembly and loaded in the page. Items are stored as the game stores them, not as text. A change to a rule in the game changes the planner on the next build of the site. The sim's tests check that the hits it rolls average to what the planner expects.

What it shows.

The character. Its level and archetype, with the archetype's Strength, Dexterity and Intelligence. Gear and gems require attributes; with Gear needs its attributes on, as the game will have it, an item or gem whose requirements aren't met does nothing.
The Rose. The passive tree, one point every two levels. Click a place to light it and the shortest road to it; point at one to see every number change. The Rose's notables and keystones are listed on the wiki.
Gear. Eight slots. Each item has its base, item level, rarity and modifiers, with every tier and its roll range. An item can be rolled the way a drop of its base, rarity and item level would be, by the game's own generator. Under Add a modifier is every affix the item can still roll, sorted by what it adds to your main skill. Point at one and every number in the sidebar shows the change. Each slot says what you would lose by taking that item off.
Skills. Six skill slots, each a skill gem with three support slots and a gem level (Auto follows your character), with the supports that would add most to that skill. Then every skill against the enemy: damage per second, average hit, uses per second, crit, mana, ignite and shock, and how long the enemy lasts. The support gems are on the wiki.
Enemy. The monster every number is measured against: its kind, level (the depth it is met at), rarity, modifiers, and whether it is shocked. There is also how hard each monster at that level hits you through your armour and resistances, and how many hits you can take.
Breakdown. Where each number comes from, from the Rose and item by item, then one use of the main skill step by step from its damage ranges to its damage per second.

How it counts. All damage is the average against one target. Crits are counted at their chance, and so are the enemy's armour and resistances. Shocked: from your hits counts the share of the time your own hits keep the enemy shocked. An ignite counts at the share of the time you keep it burning. Mana lasts as long as your full mana pool can pay for using the skill nonstop, with regeneration taken into account. Chaining and areas are listed, but the damage is always for one target.

Sharing. The address always holds the build, so a link opens it. Copy link puts the link on your clipboard. Items in a link are named by base and affix, so a link keeps working when the game adds new ones. Pin to compare keeps the current build, and every number then shows its difference from it.