how to test a claude skill before you trust it.

elisabeth hitz · june 18, 2026 · 5 min read

when you build a skill, or bundle a few into a plugin, you are really building a small product other people will use. and like anything you would hand a colleague, a template, a spreadsheet model, a checklist, it is worth a test drive before it leaves your desk. the test drive is called an eval, and it is far less intimidating than the word makes it sound.

if you are new to skills and plugins, start with claude skills, explained and claude plugins, explained. this is the step that makes them safe to rely on.

why your own skill fools you

when you use a skill you built, you know how to work around its rough edges. you know exactly what to ask, what files to hand it, and what the answer should look like. a teammate has none of that. they phrase the request a little differently, hand it slightly different inputs, or hit an edge case, an unusual-but-real situation just outside what you designed for. that is exactly where skills stumble, and the person using it won't know why.

what an eval actually is

an eval is just a try-out. a realistic request goes in, you look at what comes out, and you tell claude what to fix. no code, no test scripts, just your judgment about whether the result is good enough to put your name on.

when you build a skill with skill-creator, it walks you through this. it writes two or more realistic prompts someone might use, and for each one it produces a pair of outputs:

• one where claude uses your skill
• one where claude answers the same prompt without it

that second output is the whole point. it is the comparison. it lets you see, side by side, not just "is this okay" but "is this better than what claude would have done on its own." if your skill version isn't clearly better than the baseline, the skill isn't earning its place yet.

give feedback in plain english

as you read each pair, you are answering two questions. is the skill version the one i would actually send? if yes, note what made it better so the skill keeps doing that. if not, what is missing or off, and be specific. "the tone is too formal" or "it skipped the executive summary" gives claude something to act on. "this isn't quite right" does not.

then you submit, and your feedback is the fix. claude rewrites the instructions, adjusts the examples, tightens what it asks for, and you run the same prompts again to see if the change stuck.

change one thing at a time

if the first round showed the skill was too wordy and missing a section, pick the one that matters more, fix it, re-run, then come back for the other. that way you can tell what actually moved the needle. it is a loop, not a one-time gate, and most skills are ready after one or two rounds.

the bar for shipping, to yourself or a teammate, is not perfect evals. it is that the cases you care about pass meaningfully better than the baseline, and that you have named the cases you don't yet handle. and if the outputs already look great on the first pass, you are done. evals are there for when you need confidence, not as a hoop to jump through.

the operator's version of this

here is the habit worth keeping even outside skill-creator: before you rely on any repeatable AI workflow, run it once against a real example and ask, would i send this without editing it? if the honest answer is no, you have found the thing to fix before it ever reaches a client or a teammate. that one question is the difference between an AI setup you trust and one you quietly redo by hand.