cost-band

Preview · a replayed session in a sandbox

claude · ~/work/app · cost-band

› fix the failing auth test and add an audit log call ⏺ Read(src/auth.ts) ⎿ Read 6 lines ⏺ Update(src/auth.ts) ⎿ Added 2 lines, removed 1 line ⏺ Bash(bun test) ⎿ 3 pass, 1 fail ● Done. refresh now rejects expired claims and logs an audit event. ✻ Worked for 42s · done 4:20 PM Last turn $0.420 · Session $0.420 · list-price estimate, not a bill ────────────────────────────────────────────────────────────────────────────────────────────────────────────────────── › ? for shortcuts

Draws

Band

Last turn $0.420 · Session $0.420 · list-price estimate, not a bill

README

mateai-mods

Small Claude Code mods from the MateAI channel.

A band above the prompt that shows what the last turn and the whole session would cost at API list prices:

Last turn $0.042 · Session $0.318 · list-price estimate, not a bill

The mod reads the session cost Claude Code already computes (the same number as "Total cost" in /usage). It contains no price table, so there are no hard-coded rates to go stale.

Requirements

Claude Code 2.1.287 or later, or the Desktop app 2.1.286 or later (mods do not exist in older versions).
Not available in Desktop WSL sessions.

Check your version with claude --version (terminal) or /status (Desktop, local session).

Install

From a terminal:

claude plugin marketplace add mategog/mateai-mods
claude plugin install cost-band@mateai-mods

Or inside a Claude Code session:

/plugin marketplace add mategog/mateai-mods
/plugin install cost-band@mateai-mods

Then restart the session. The band appears above the prompt after the first completed turn.

Update and remove

claude plugin marketplace update mateai-mods
claude plugin disable cost-band@mateai-mods
claude plugin marketplace remove mateai-mods

Read it before you install it

Mods are not sandboxed. A mod runs inside Claude Code with your permissions, so it could read your files and environment variables, start programs and use the network. Only install mods from people you trust, and read the code first. This one is short:

File	What it does
`plugins/cost-band/hooks/register.tsx`	On `turn.complete` it reads `session.usage()`; on `ui.render` it draws the band.
`plugins/cost-band/hooks/cost.ts`	Pure functions: last-turn math and `$` formatting.
`plugins/cost-band/hooks/hooks.json`	Registers the module.

It makes no network calls and starts no processes. You can also check what any mod registers without running it:

claude plugin validate plugins/cost-band

What the number is, and is not

It is a list-price estimate computed locally from token counts. It is not your bill. The Claude Code docs say it is not relevant for billing on Pro and Max plans.
It shows how much work you asked the model to do. It says nothing about what any company earns or spends.
If the session reports no cost, the band says Cost estimate unavailable in this session.
After /clear the session total starts over, and so does the last-turn figure.

Layout

.claude-plugin/marketplace.json      marketplace "mateai-mods"
plugins/cost-band/                   the plugin
  .claude-plugin/plugin.json
  hooks/{hooks.json,register.tsx,cost.ts}
  hooks/*.test.ts                    unit tests for the cost math and registration
  types/index.d.ts

License

MIT. See LICENSE.

Source 3 files

hooks/register.tsx 36 lines

1import { atom, read, update } from 'claude-code'
2import type { Register } from 'claude-code'
3
4import { formatUsd, nextCost, START } from './cost'
5
6const cost = atom({ plugin: 'cost-band', key: 'cost' } as const, START)
7
8export const register: Register = on => {
9  on('turn.complete', async ($, e, next) => {
10    const usage = await $.session.usage()
11    await update($, cost, prev => nextCost(prev, usage.cost?.usd))
12
13    return next(e)
14  })
15
16  on('ui.render', { component: 'AbovePrompt' }, async ($, e, next) => {
17    const { turns, total, last } = await read($, cost)
18
19    if (e.props.hasSurvey || turns === 0) {
20      return next(e)
21    }
22
23    const { Box, Text } = $.ui.resolve(e)
24
25    return (
26      <Box>
27        <Text dimColor>
28          {total === null || last === null
29            ? 'Cost estimate unavailable in this session'
30            : `Last turn ${formatUsd(last)} · Session ${formatUsd(total)} · list-price estimate, not a bill`}
31        </Text>
32      </Box>
33    )
34  })
35}
36

hooks/cost.ts 17 lines

1import type { Cost } from '../types'
2
3export const START: Cost = { turns: 0, total: null, last: null }
4
5// `usd` is the session's running total; a total below the previous one means /clear started over.
6export function nextCost(prev: Cost, usd: number | undefined): Cost {
7  if (usd === undefined) return { turns: prev.turns + 1, total: null, last: null }
8
9  const before = prev.total === null || usd < prev.total ? 0 : prev.total
10
11  return { turns: prev.turns + 1, total: usd, last: usd - before }
12}
13
14export function formatUsd(n: number): string {
15  return '$' + n.toFixed(n < 1 ? 3 : 2)
16}
17

types/index.d.ts 8 lines

1export type Cost = { turns: number; total: number | null; last: number | null }
2
3declare module 'claude-code' {
4  interface PluginState {
5    'cost-band': { cost: Cost }
6  }
7}
8