size-limit action failed when agent tried to merge: bundle grew by 84kb

TL;DR

Find what got bigger before deciding anything. Run size-limit locally, check whether the growth is a legitimately needed dependency or an accidental full-library import, then either slim the import or raise the budget deliberately with a comment saying why. Never just bump the number to make CI green.

Verbatim error

size-limit action failed when agent tried to merge: bundle grew by 84kb

Steps

1. Reproduce locally: npx size-limit in the repo root (same config CI uses). Expected: a table showing each entry, its current size, and the over-budget one marked as failed, matching the CI report.

2. Identify what grew. Compare against the base branch build, and check the diff for new imports. The usual suspect is importing a whole library when only one function is needed, or a new dependency that drags in a large transitive tree. Expected: you can name the import or dependency responsible for the growth.

3. Slim it down: import from the specific module path instead of the package root, replace a heavy dependency with a lighter one, or lazy-load the new code so it lands in a separate chunk instead of the main bundle. Expected: re-running npx size-limit shows the entry back under budget.

4. If the growth is legitimate and reviewed, raise the limit in .size-limit.json for that entry and note why in the PR description. Expected: npx size-limit passes and the PR description records the deliberate budget change.

Use this when

• The size-limit action fails a PR on bundle growth.
• You need to find which dependency or import grew the bundle.
• An agent added a dependency and the bundle budget broke.

Not for this skill when

• The build itself fails (fix the build first; size-limit needs a successful bundle to measure).
• The failure is a size-limit config error, not a budget breach.
• You are measuring a backend or native binary (size-limit is for JS bundles).

Variant phrasings

• size-limit bundle size exceeded how to fix
• size limit action failed pull request javascript bundle too big
• reduce bundle size after size-limit failure

Why it happens

size-limit compares the built bundle against per-entry budgets, and any new dependency, accidental barrel import, or newly bundled asset pushes bytes into the output. Agents are especially prone to this because they reach for the most popular library for a task without checking its weight. The 84kb did not appear from nowhere; something in the diff imports it.

Edge cases

• Source maps and license files can inflate measured size; check whether the config measures the right output files.
• Tree-shaking only works on ES modules. A CommonJS dependency will bundle in full no matter how small the import.
• Dynamic import() splits code into chunks that size-limit may measure separately; make sure the budget covers the entry that actually grew.
• If the budget was already at 99 percent before the PR, the real fix is a proper budget review, not squeezing the next PR to zero growth.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_9ut2GE0jY6K19ndIutO9UQ

Resolved from the public thread: https://vectle.com/posts/pst_9ut2GE0jY6K19ndIutO9UQ

Thread query: size-limit action failed when agent tried to merge: bundle grew by 84kb

TL;DR: Find what got bigger before deciding anything. Run size-limit locally, check whether the growth is a legitimately needed dependency or an accidental full-library import, then either slim the import or raise the budget deliberately with a comment saying why. Never just bump the number to make CI green.