# Instacalc

> Instacalc is a plain-text calculator designed for readability and inspection
> — like Markdown for math, looking like what you would jot down on a napkin.
> Every calc is plain text (.ic) encoded statelessly in a URL — no login, no
> database, no API call required. Write `bill=50;tip=bill*0.20`, get a
> shareable, embeddable, live-editable calculator that anyone can inspect, fork,
> and re-share. Calcs can also load external data from GitHub or URLs via import().

## Skill / agent setup

- [Instacalc for AI](/ai) — install the skill (Claude Code, Claude app), or
  the one-line prompt for any other assistant.
- [/claude/SKILL.md](/claude/SKILL.md) — the skill itself: how to model a
  problem as a calc, size it, and mint a share link. Fetch and follow it.
- [/claude/ic-format.md](/claude/ic-format.md) — every decorator, control and
  chart, plus the failure modes that render a silently wrong number.
- [/claude/ic-link.mjs](/claude/ic-link.mjs) — zero-dependency Node script:
  `.ic` in, share links out, and `--decode` to verify one round-trips.

## Syntax & URL reference

- [Full syntax + URL encoding reference](/llms-full.txt) — variables, units,
  sliders, graphs, calculus, goal-seek, and exactly how to encode a calc into
  a shareable URL, with worked examples.

## Examples

- [Gallery](/gallery) — hundreds of live example calcs across finance,
  health, engineering, and everyday math.

## Fetching a calc as Markdown

Append `.md` to any calc URL, or send `Accept: text/markdown`, to get that
calc's source (title + rows) back as clean Markdown instead of the full HTML
page — useful for pulling an existing calc's formulas into context before
modifying it.