# Show HN: Slash-tokens – know LLM cost before the call leaves your machine

> Source: <https://github.com/Wolfe-Jam/slash-tokens>
> Published: 2026-08-25 22:48:31+00:00

Token Optimization for Context Engineers. For anyone building with LLMs. 4.8 KB WASM. Sub-millisecond. Zero dependencies.

Know the cost before the call leaves your machine.

Models change. Windows grow. Slash adapts — you keep building. Cheaper tokens haven't shrunk the bill — usage has.

Current: [slash-tokens@1.6.5](https://www.npmjs.com/package/slash-tokens) · [release notes](https://github.com/Wolfe-Jam/slash-tokens/releases/tag/v1.6.5)

```
bunx slash-tokens
# or: npx --yes slash-tokens
```

Run it in a project that already calls an LLM. An empty folder prints that nothing was found — that's normal.

See it work in a chat: [live demo](https://slash-nextjs-wofejams-projects.vercel.app)

```
npm install slash-tokens
bun add slash-tokens
```

One import. Every LLM call checked pre-call.

```
import 'slash-tokens/auto'
```

Intercepts `fetch()`

to Anthropic, OpenAI, xAI, and Google endpoints. Estimates tokens before the call leaves your machine. Sub-millisecond. Non-blocking.

```
[slash] Anthropic claude-sonnet-5 | 47,000 tokens | $0.0940 | OK
[slash] xAI grok-4.6 | 12,300 tokens | $0.0246 | OK
```

`preflight`

is analysis (every cheaper model, all providers). `preflightRoute`

is the routing decision — same provider only. They answer different questions.

``` js
import { preflight, preflightRoute } from 'slash-tokens'

const prompt = 'Your prompt here...'

const check = preflight(prompt, 'claude-opus-5')
check.tokens       // estimated tokens
check.cost         // USD at the input rate
check.fits         // under this model's context window?
check.options      // cheaper models across providers — not a route

const route = preflightRoute(prompt, 'claude-opus-5')
// cheapest same-provider alternative, or null
// e.g. { model: 'claude-haiku', cost, salvaged, salvagePercent }
```

Fully typed. Do not use `check.options[0]`

as the route — that list is cross-provider on purpose.

The engine underneath. 4.8 KB Zig-compiled WASM, calibrated against real provider tokenizers — not a flat chars/4 guess.

``` js
import { slash, slashBytes } from 'slash-tokens'

slash('Hello world')            // 2
slash(longDocument)             // 47283
slashBytes(new Uint8Array(buf)) // skip TextEncoder
```

Safe pre-check, not a perfect count. Pre-call, you only need go/no-go.

Live ladder as of 2026-08-25. Generic aliases (`claude-opus`

, `gpt-5.4`

, `grok-4.20`

, …) still resolve. Don't see yours? [Open an issue.](https://github.com/Wolfe-Jam/slash-tokens/issues)

| Model | $/M input | $/M output | Context |
|---|---|---|---|
| claude-opus-5 | 5.00 | 25.00 | 1M |
| claude-sonnet-5 | 2.00 | 10.00 | 1M |
| claude-haiku-4.5 | 1.00 | 5.00 | 200K |
| grok-4.6 | 2.00 | 6.00 | 500K |
| grok-4.3 | 1.25 | 2.50 | 1M |
| gemini-3.1-pro | 2.00 | 12.00 | 1M |
| gemini-3.5-flash-lite | 0.30 | 2.50 | 1M |
| gpt-5.6-sol | 4.00 | 20.00 | 1.05M |
| gpt-5.6-terra | 2.00 | 12.00 | 1.05M |
| gpt-5.6-luna | 0.20 | 1.20 | 1.05M |

``` js
import { listModels, MODELS } from 'slash-tokens'

listModels()
MODELS['grok-4.6']  // { input: 2, output: 6, context: 500000, ... }
```

Optional. `bunx`

is the try path — no account.

``` js
import { init, report } from 'slash-tokens'

init({ key: 'mcp_slash_xxx' })

const result = await report({
  tokens_estimated: 47000,
  tokens_saved: 47000,
  model: 'claude-opus',
  action: 'skipped',        // 'skipped' | 'reduced' | 'routed'
  cost_saved_usd: 0.235
})
```

Hosted dashboard is ordinary SaaS: $39/mo or $390/yr for the data, not a cut of savings. One-person key: [mcpaas.live/slash/setup](https://mcpaas.live/slash/setup)

Node.js, Bun, Deno, Cloudflare Workers, Vercel Edge, Browser.

TypeScript SDK tests via `cd npm && bun test`

. Zig coverage includes adversarial cases (CJK, emoji, binary, base64, thresholds).

**Code: MIT.** Fork it, ship it, change it, show it, share it, sell it.

**Brand: reserved.** The slash-tokens name, ⚡ mark, and red/gold colors stay with the project. If you're building on top of the SDK, ship under your own name and colors — don't represent your app as Slash. See [NOTICE](/Wolfe-Jam/slash-tokens/blob/main/NOTICE).

🏎️ *Don't go to the Corner Shop in a Ferrari.*