Spellcrafting

Spellcrafting is the work of shaping new spells and setting spells down in writing. Every spell in the spell compendium was invented by someone, and the Aethyrweave can still be woven into patterns nobody has tried. Spells long forgotten can be found again, and new ones discovered, by casters with enough power and wisdom.

Spell Discovery

The main way to invent a spell is the Spell Discovery technique advancement, open to Spellcasters. When you gain it, you design a new spell, from scratch or by reworking an existing one, with your GM’s approval:

Order. You choose the spell’s level, from 1st to 9th Order, which sets its minimum slot and its dice potency.
Domain. The spell belongs to your spellcasting domain, Arcane, Divine or Natural, which limits its damage types, how its healing works and the schools it fits.
Components. Somatic, verbal and material components, including costly materials, change the spell’s potency.
Free casting. The spell doesn’t count against your spells known or prepared, and you can cast it without a slot: three times a day at 3rd level for a 1st- to 3rd-Order spell, twice at 6th level for a 4th- to 6th-Order spell, or once at 9th level for a 7th- to 9th-Order spell.

The feature’s own page has the full design guidance.

The Spellcrafting Check

Outside Spell Discovery, spellcrafting calls for a spellcrafting check: an Intelligence (Arcana) check for an arcane spell, or a Wisdom (Religion) or Wisdom (Nature) check for a divine or natural one. The DC is 10 plus twice the spell’s level. If you fail by 5 or more, the half-woven spell breaks loose: the GM calls for a surge check with a Surge Charge equal to the spell’s level.

Use it for work like this:

Researching a spell. With the GM’s agreement, a spellcaster can recreate a lost spell or invent one they could otherwise only gain through Spell Discovery. Treat this as Researching downtime: the GM sets how long it takes and where the knowledge can be found, and the work ends with a spellcrafting check. On a failure, the research continues for another week before you can try again.
Adapting a spell on the fly. Changing one detail of a spell as you cast it, such as its damage type or the shape of its area, takes a spellcrafting check before the spell is cast. On a failure, the spell is cast as normal. Features like Awakened Spellbook let their owners make some of these changes without a check.

Recording Spells

Spellbooks and ritual books. Copying a spell into a book you cast from takes 2 hours and 50 gp per level of the spell, as the Ritual Caster feature describes for ritual books.
Spell scrolls use the SRD rules below.

From the SRD 5.2.1: scribing spell scrolls

A spellcaster can transfer a spell to a scroll and create a Spell Scroll, using the rules below.

Time and Cost

Scribing a scroll takes an amount of time and money based on the level of the spell, as shown in the Spell Scroll Costs table. For each day of inscription, you must work for 8 hours. If a scroll requires multiple days, those days needn’t be consecutive.

Prerequisites for the Scribe

To scribe a scroll, you must have proficiency in the Arcana skill or with Calligraphy Tools and have the spell prepared on each day of the inscription. You must also have at hand any Material components required by the spell; if the spell consumes its Material components, they are consumed only when you complete the scroll. The scroll’s spell uses your spell save DC and spell attack bonus.

Cantrips

If the scribed spell is a cantrip, the version on the scroll works as if the caster were your level.

Spell Scroll Costs

Spell Level	Time	Cost
Cantrip	1 day	15 gp
1	1 day	25 gp
2	3 days	100 gp
3	5 days	150 gp
4	10 days	1,000 gp
5	25 days	1,500 gp
6	40 days	10,000 gp
7	50 days	12,500 gp
8	60 days	15,000 gp
9	120 days	50,000 gp