Per-customer LLM spend caps for micro-SaaS builders

What to build

A lightweight proxy/middleware service for solo AI micro-SaaS builders that sits between their app and OpenAI/Anthropic API calls, tracking per-customer token spend in real time, enforcing hard caps or auto-throttling, and sending Slack/email alerts before a single account's usage erodes the builder's margin.

Solo AI micro-SaaS builders have no easy way to see or cap per-customer LLM spend, so a single abusive or buggy account can quietly cost more than it pays in subscription revenue.

Demand

Builders running usage-based AI products on thin margins want this now because LLM costs scale per-request while pricing is flat, and a single runaway customer can wipe out a month of profit before anyone notices.

• r/microsaasDiscussion

  Reddit thread asking AI micro-SaaS founders whether any single customer has cost them more in API spend than they pay in subscription revenue, surfacing this as a shared pain point among builders calling OpenAI/Anthropic on behalf of users.

Stack

• OpenAI API
• Anthropic API
• Redis (rate limiting/counters)
• Postgres
• Stripe metered billing
• Slack API

Solo + AI difficulty

The core loop (intercepting API calls, metering tokens, enforcing caps) is a well-scoped weekend build for one person with AI help; the hard part is building trust as a man-in-the-middle for production API keys and handling edge cases like streaming responses and multi-provider token counting.

Entry threshold

A usage-tracking proxy with alerting and a simple dashboard is buildable solo with AI tooling in one to two weeks, but getting other developers to route production API traffic through a third-party layer requires trust, so initial distribution leans on build-in-public credibility rather than cold outreach.

Window

6-12 months

Where to find first users

• r/microsaas
• r/SaaS
• Indie Hackers
• Product Hunt launch

Competitors

• Helicone
• Portkey
• LiteLLM
• Cloudflare AI Gateway

Counter-signals & risks

• Established API gateway tools (Helicone, Portkey, LiteLLM, Cloudflare AI Gateway) already offer usage tracking, budgets, and rate limiting, which reduces the need for a standalone third-party proxy.

• Micro-SaaS builders are highly price-sensitive and may choose to build simple per-customer cap logic themselves rather than integrate another paid vendor.

• The signal is a single anecdotal forum question with no quantitative data on market size, willingness to pay, or how often this cost-overrun problem actually occurs.