The Two-Tool Problem: ESLint, Prettier, and the Case for a Unified Toolchain

Deep dive · Tooling · ~18 min read · ESLint · Prettier · Biome · TypeScript Most JavaScript projects ship with both ESLint and Prettier without anyone really understanding why two separate tools are needed — or why combining them into one is harder than it looks. This is the post that should have existed when I first set up a new project and stared at four config files doing roughly the same thing. Table of Contents The right mental model, first ESLint: what it actually does under the hood Prettier: why it reprints instead of fixing The overlap zone: where things get messy Configuring both properly in 2026 Why one tool couldn't do this for so long Biome: the serious attempt at unification A real comparison across a codebase What Biome still cannot do Verdict and migration strategy The right mental model, first The confusion starts because both tools ship as dev dependencies, both produce errors in your terminal, both integrate with your editor, and both run in CI. They touch the same f