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

Slash-tokens 1.6.5, a 4.8 KB WASM library that estimates LLM token counts and costs before API calls leave the machine, is now available on npm. The tool intercepts fetch() calls to Anthropic, OpenAI, xAI, and Google endpoints, providing sub-millisecond preflight checks and routing decisions. It supports models like claude-opus-5 at $5.00/M input and gpt-5.6-luna at $0.20/M input, with an optional hosted dashboard at $39/mo.

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.