S-Calc

S-Calc adds a code block to Obsidian that does quick math without leaving the note. Write expressions in an s-calc block and each line's answer appears on the right of that line, in your theme accent colour, live as you type and in reading view. It works like Soulver or Numi, but native to Obsidian. It handles arithmetic with parentheses, variables and labels you can reuse later, running totals with sum and prev, percentages including reverse ones, unit conversion, live currency for every currency the rate feed returns, and plain-language dates like next friday + 2 weeks.

Notes are full of small calculations: a price minus a discount, a unit conversion, a currency amount, a date a few weeks out. The usual flow is to alt-tab to a calculator, work it out, and copy the number back. That breaks the writing and loses the context the number belongs to. Obsidian had no built-in way to do the math in the note itself.

The plugin is split into small, testable pieces. A pure evaluate(lines) engine runs each line against a shared scope, so labels and the sum/prev keywords carry down the block. It preprocesses the parts a math library can't read directly (percentage phrases, in conversions, date arithmetic), evaluates with mathjs, falls back to chrono-node for dates, and formats the output. A currency module fetches USD-based rates once per session from a free no-key endpoint (open.er-api.com) and registers every returned currency as a mathjs unit, with name aliases so 4 GBP in euro resolves. A CodeMirror 6 view plugin finds s-calc fences and paints a right-aligned result per line, which is the live-while-typing part, plus a reading-view processor for the rendered note. Results read Obsidian's own theme variables, so they use the accent colour and match light and dark mode with no rebuild. It started from a Svelte plugin template; Svelte, Tailwind, and shadcn were stripped out because a code-block processor needs none of them, leaving two runtime dependencies.