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skill-improve is a skill from the Summer skill library: a guide your AI agent reads when the task matches, so it builds the good version on the first try. Upgrade an underperforming Summer skill — run it against a behavioral spec with and without changes via a parallel-eval harness; ship the winner.

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When your agent uses it

  • A contributor wants to upgrade a Summer skill that is underperforming or to fix a regression
  • Comparing a skill with and without a change against a behavioral spec before shipping the winner

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Install

summer setup installs every skill for your agent. To add only this one:
Swap claude-code for your agent, such as codex or cursor. See Skills for every option.

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The skill

Adapted from the skill-creator skill in anthropics/skills. Use when a skill’s behavioral spec fails assertions or the skill produces low-quality output.

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When to use this vs. /skill-test

  • /skill-test spec reasons over text. Cheap and fast, but lossy.
  • /skill-improve runs the skill in parallel subagents, with and without the proposed changes. Slower and more expensive, but accurate.
Run this when /skill-test spec flags issues you can’t fix by reading the skill alone.

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Steps

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1. Pick the skill + the spec

Ask the user:
  • Skill slug. Resolves to library/skills/<slug>/SKILL.md.
  • Test cases to focus on. Default: all ## Case blocks in evals/skills/specs/<slug>.md.

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2. Establish a baseline

For each Case:
  1. Spawn a subagent (Task tool, general-purpose) with the current skill body in context.
  2. Give it the Case’s Input + Fixture.
  3. Capture the tool calls it makes and the diff it produces.
  4. Score against the Case’s Assertions.
Save outputs to tests/runs/<skill-name>/baseline/case-<N>/.

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3. Propose changes

Read the failing Cases. Identify the gap between what the skill says and what the agent did. Common gaps:
  • Skill names a tool but the agent picked a different one (clarify the trigger).
  • Skill assumes a fixture detail the agent missed (add explicit step to confirm).
  • Skill’s “May I” wording is too generic for the agent to infer the right ask.
Draft a revised SKILL.md. May I write it to tests/runs/<skill-name>/proposed/SKILL.md?

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4. Run the proposed version

Repeat step 2 with the proposed SKILL.md. Save to tests/runs/<skill-name>/proposed/case-<N>/.

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5. Compare and decide

For each Case, score:
  • Assertions passed (proposed vs. baseline).
  • Tool-call efficiency (fewer tools = better, all else equal).
  • Hallucination / unwanted ops (penalize).
Output:
If proposed wins on net, prompt the user:
Proposed version wins 2 cases, ties 1, loses 0. May I overwrite library/skills/<slug>/SKILL.md with the proposed version?

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6. Ship

On user yes:
  • Overwrite SKILL.md and bump version in resource.yaml.
  • Commit with message feat(skill): improve <name> — <one-line summary of change>.

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Collaborative protocol

This skill writes files at multiple steps. Always ask before each write.

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See also

  • skill-test
  • tests/runner.md
  • evals/skills/specs/
  • skill-test: Lint a Summer skill before commit, audit the whole library, or check a behavioral spec assertion — static structural rules plus behavioral specs.
Source: library/skills/skill-improve/SKILL.md, rendered from summer-engine@4.3.0 on npm.