A free standalone micro-tool that feeds sign-ups to the main product

A free micro-tool is a small, separate product that does one useful job with no login, then passes the result into your main product. Eraser says its DiagramGPT sidecar is now its biggest growth driver, at 30% of new sign-ups. ProfitWell gave away a full metrics product and built paid tools on its data, but published no link from free usage to revenue.

How it works

The tool is a feeder. It wins attention on its own terms, then routes the people who want more into the product you charge for. Treat it as a growth loop with one exit: the handoff.

1. Pick one narrow job next to your core product. Eraser is a docs and diagrams tool for engineering teams, founded in November 2020. In May 2023 it shipped DiagramGPT, which generates diagrams from plain language or code snippets.
2. Build it outside the core product. Eraser chose a sidecar so the new tool would not have to meet the polish standard of its core features, which let it ship fast.
3. Give it its own name. Eraser made a deliberate call to brand the tool as DiagramGPT, apart from the Eraser brand.
4. Drop the gate. The tool is ungated, and Eraser had already experimented with an ungated product experience before this.
5. Make the handoff one click. The DiagramGPT page offers a "Save and Edit Diagram" path that moves the output into Eraser for further editing. The same page also points teams with custom diagram workflows toward a sales conversation.

Eraser's founder explains the sidecar and branding choices in a Growth Unhinged write-up of the sidecar, and our summary sits on the Eraser case page.

ProfitWell ran a heavier version. Its free product was a complete revenue reporting tool for subscription and SaaS companies, described on the ProfitWell Metrics product page as completely free. In a Business of Software talk, the founder said the company made money by studying that data and building paid products for churn reduction and price optimization. See the ProfitWell case page.

What it takes

Our estimate: about 80 hours of work, and about 30 days before you can read a signal. Most of the hours go into the tool itself, a simple landing page, and the handoff that carries the user's output into your product without retyping it. Tracking the source of each sign-up takes less time but is the part teams skip. A month gives search and word of mouth time to bring in enough users that the handoff rate stops swinging week to week.

What to measure

Share of sign-ups from the tool tells you whether it matters at all. Read it as a trend, not a single month.

Handoff rate is the core of the tactic. High tool usage with a low handoff rate means you built a popular free product that does not feed your business. A rising handoff rate after you change the button or the saved output is the clearest win you can get.

Activation and paid conversion of tool-sourced accounts tell you whether these users are your buyers. Compare them against other channels using a shared definition of activation and the same cohort window. If tool users activate well but rarely pay, the tool is attracting the wrong audience.

Tool sessions sit upstream. If they fall, fix distribution before touching the handoff.

When it backfires

• No handoff. Without a step like Eraser's save and edit path, users take the output and leave.
• The free tool becomes the whole product. ProfitWell gave away a full product and earned money from separate paid products built on its data. If your paid offer is not clearly bigger, free can cannibalize it.
• A separate brand hides the parent. Eraser split the brand on purpose, which means the handoff page has to explain who you are, or the brand gap costs you sign-ups.
• Running costs on ungated use. DiagramGPT runs on OpenAI's models. If your tool calls a paid model, every anonymous use costs money, so set rate limits before launch.
• Crediting the tool for all growth. Eraser's sign-ups grew 20x in a year, but the source does not tie that to DiagramGPT.

Run it as an experiment

We recommend this hypothesis: a one-click handoff from the free tool will raise tool-sourced sign-ups without lowering their activation rate compared with other channels.

For the first version, use a before and after comparison with a fixed 30-day window, measuring tool-sourced sign-ups against your baseline mix. Once traffic is steady, split the handoff: half of tool users see the save into product button, half see only a plain link. Size the split with the sample size calculator.

Log the tool session, whether the user clicked the handoff, sign-up source, activation within your normal window, and paid conversion. Our suggested decision rule: keep and invest if the handoff variant lifts sign-ups and tool-sourced activation is at least on par with other channels. Kill or rework it if usage grows but handoff stays flat for two windows. The growth experiment guide has a write-up template, and the growth model template has a loop row for the tool.

How strong the evidence is

The grade is case with numbers: at least one company documented the tactic and published the result as numbers, quoted by name. Eraser carries the grade, with its founder stating that DiagramGPT accounts for 30% of sign-ups at the time of writing. That figure is a share, with no baseline and no paid conversion attached, so it shows reach, not revenue. ProfitWell adds a usage count of about 35,000 companies, a later figure. Neither number is tied to paid sign-ups, so ProfitWell shows that a free product can win wide use, not that the use paid.