Ask for a regex, then attack its assumptions

Why this matters

A regex for a limited filter is not a complete email validator. Decide whether a hyphen must occur in the local part or anywhere in the address, whether subdomains count and whether matching is case-insensitive. The activity test runner uses a short-lived worker and synthetic strings, not a production data scan.

Before you start

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Your illustrated field guide

Conceptual illustration, not a provider screenshot. Artwork is AI-generated; instructional labels are authored text.

Start with fictional input

Specification: local part must contain a hyphen; domain is one simple label followed by .edu; no spaces; case-insensitive. Match: first-last@example.edu; A-B@COLLEGE.EDU. Reject: firstlast@example.edu; first-last@example.com; firstlast@my-college.edu; first-last@dept.example.edu.

Copy and adapt this prompt

Propose a bounded JavaScript regex for exactly the stated simplified filter, not RFC-complete email validation. Explain the anchors, local-part hyphen rule, simple domain and case-insensitive flag. Provide results for all supplied tests and at least two edge cases. Do not claim it verifies delivery or institutional status.

Worked reference—not proof of correctness

One limited pattern: ^[A-Z0-9._+]*-[A-Z0-9._+-]*@[A-Z0-9]+(?:-[A-Z0-9]+)*\.edu$ with i flag. Check its actual behaviour; “a-b@example.edu” is a match, while a hyphen only in the domain is insufficient. The simplified grammar intentionally excludes some valid real addresses.

Five practical steps

1. Define the policy

   Write the exact location of the hyphen and domain/subdomain rules before asking for syntax.

2. Get a draft pattern

   Request the target engine and flags; do not copy syntax intended for a different language.

3. Run the fixture

   Use the bounded test tool and compare actual results with the reference list.

4. Try edge cases

   Add spaces, an empty local part and uppercase letters; keep false positives and negatives visible.

5. State the scope

   Label the filter as a toy policy check, not email validation or proof of eligibility.

Test your result

• All six supplied strings have recorded expected and observed results.
• A hyphen only in the domain does not satisfy the local-part requirement.
• The report names JavaScript/flags and clearly limits the simplified grammar.

Mistakes to watch for

• Calling a matching string a deliverable or institution-verified email address.
• Using an unbounded pattern or huge input without a timeout.

Offline / no-key route

Mark expected matches by hand and explain the policy without executing a pattern.

Reflect

Which valid real-world address might your deliberately simplified filter reject?

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