SAP for AI Agents

StringCost: Think SAP for AI Agents.

A revenue-first framework that creates a double-entry ledger for every agent operation. Stop building on shallow proxies. Start building on a true system of record for your AI business.

Revenue-firstAudit-readyAgent-native

Andreessen Horowitz just declared:

“AI is driving a shift towards outcome-based pricing. Software is becoming labor.”

But where is the infrastructure for outcome-based billing & accounting?

This not a payments problem, but an accounting problem that leads to catastrophic failure. The future is outcome based...but the tools to build it don't exist.
Until now.

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The Root Cause: A New Cost Paradigm

Why is monetizing AI agents so difficult? Because the financial models that powered the last decade of SaaS are fundamentally broken in the world of Generative AI.

OLD

SaaS APIs

Predictable, Per-Call Cost

API calls have a fixed, amortizable compute cost. The size of the JSON payload has a negligible impact on the price.

Billed by the Request

The billable event is the API call itself.

NEW

Agentic APIs

Variable, Computational Cost

An agent's cost is directly tied to the “work” it performs. It's a metered, computational resource, not a fixed endpoint.

Billed by the Computation

The billable events are the input tokens, output tokens, the number of thoughts, and every downstream tool call the agent makes.

This creates a massive accounting problem that traditional billing systems cannot solve. Trying to price a variable, multi-step agentic workflow like a simple API call forces you to either guess—and consistently underbill or overcharge your customers—or build a complex, brittle accounting system from scratch.

The Double-Entry Ledger for AI Agent Operations

Simple token counters and API proxies are failing. They see the token count and total bill from your model provider, but they can't tell you the profitability of a single agent run.

Deep Framework Integration

StringCost isn't a language-level library; it's a compile-time harness for your framework. We integrate directly into the build and deployment lifecycle. For our first target, Next.js, we use deep framework-level tools like the Vercel Build Output API to package your agents and their instrumentation together, ensuring perfect compatibility and control over the deployment environment.

Every Step is a Ledger Entry

Our step primitive is the core of this ledger. It forces every discrete computational action to be recorded as a distinct line item with two sides:

Cost Side (Debits): The tokens you paid, the price of the tool call, and the compute time.
Revenue Side (Credits): The billable event for your customer based on your pricing model.

The result is a perfect, auditable, real-time P&L for every single agent run. You can finally answer critical business questions: “Which agents are most profitable?”, “Which tools are driving the most cost?”, and “What is the true margin on our AI features?”

An End-to-End System for Profitable AI Operations

StringCost provides a cohesive set of primitives that transforms your agent's logic into a fully instrumented, deployable, and billable asset.

Design for Revenue with Billable Primitives

Our Inngest-like developer experience keeps your team shipping. Every `step` wraps logic and turns it into a traceable, auditable, billable event.

// Every step is a line item on a future invoice.
const thought = await step({
  name: "Analyze User Intent",
  actionType: "llm_call",
  unitCost: 0.001
}, ...);

const dbResult = await step({
  name: "Query Customer DB",
  actionType: "tool_use",
  unitCost: 0.005
}, ...);

Deploy with Confidence on Vercel

Stop choosing between flexibility and scalability. Leverage Vercel's Build Output API to ship custom runtimes with serverless performance.

// vercel.json — full control of the build.
{
  "buildCommand": "node build.js",
  "outputDirectory": ".vercel/output",
  "framework": null
}

// build.js — package tools as optimized functions.
class VercelCustomBuilder {
  async build() {
    await this.buildMCPFunctions(); // API wrappers
    await this.buildAgentFunctions(); // Agent logic
  }
}

Integrate Seamlessly with Your Financial Stack

Native Stripe utilities power real-time usage tracking, subscription gating, and invoice automation—tying every agent action straight into revenue.

// lib/framework.ts — automatically track usage.
import { trackUsage } from '@/lib/stringcost/server';

class BillingManager {
  async record(event) {
    await trackUsage({
      userId: this.userId,
      featureId: event.actionType,
      usage: Math.round(event.cost * 1000) || 1,
    });
  }
}

// middleware.ts — protect premium features.
import { checkEntitlement } from '@/lib/stringcost/server';

export async function middleware(request: NextRequest) {
  if (request.nextUrl.pathname.startsWith('/premium-agents')) {
    const { hasAccess } = await checkEntitlement({ /* ... */ });
    if (!hasAccess) {
      return NextResponse.redirect(new URL('/pricing', request.url));
    }
  }
}

Built for Every Team in Your Organization

Every team gets the visibility and control they need without rebuilding billing infrastructure from scratch.

Product

For Product Teams

Go to market with complex, usage-based pricing models in days, not quarters. Experiment with billing per-action, per-thought, or per-tool.

Engineering

For Engineering Teams

Build any agent imaginable with a Next.js-native DX while the framework handles billing, observability, and compliance-grade audit trails.

Finance & Ops

For Finance & Ops

Eliminate billing errors with a perfect record of every billable action. Sync usage to Stripe for invoices your customers—and auditors—can trust.

Flexible Accounting for Any AI Business Model

This double-entry approach unlocks any pricing strategy you can imagine.

01 · Tiered

Tiered & Hybrid Billing

Assign different costs and prices to different actions. Charge more for premium tools or more powerful models.

// Agent Code
await step({
  name: "Basic Analysis",
  actionType: "llm_call",
  unitCost: 0.001
}, ...);

await step({
  name: "Premium Data Tool",
  actionType: "tool_use",
  unitCost: 0.050
}, ...);

// Resulting Ledger
// DEBIT: Cost of gpt-4-turbo tokens
// CREDIT: $0.0010 revenue
// DEBIT: Cost of Premium Data API
// CREDIT: $0.0500 revenue

02 · Dynamic

Dynamic & Performance-Based Billing

The price of a step can be calculated at runtime. Charge based on execution time, ensuring your margins are always protected.

// Registering a tool with
// a dynamic cost function
McpRegistry.register(
  'dataApi',
  '...',
  (metrics) => {
    // Base fee + time-based markup
    const timeCost = Math.floor(
      metrics.durationMs / 100
    ) * 0.005;
    return 0.01 + timeCost;
  }
);

03 · Outcome-Based

Outcome-Based Billing: Only Pay for Results

Build ultimate trust with your customers. Since every step captures execution outcome, you can design billing models that only create a revenue entry for successful actions.

// Your billing logic
function processBillingEvent(event) {
  // The COGS (debit) is always
  // recorded, but the revenue
  // (credit) is conditional
  if (event.outcome === 'success') {
    chargeCustomer(
      event.userId,
      event.cost
    );
  }
}

Stop Building on Proxies. Start Building on a System of Record.

Schedule a demo to see how StringCost's double-entry ledger can give you the financial control to ship profitable AI agents with confidence.

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