402utils Regex Test & ReDoS Guard

x402

402utils Regex Test & ReDoS Guard is a paid API for AI agents from 402utils.com, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-10).

Tests a regex pattern against one or more input strings using match, matchAll, or replace modes, with a mandatory static ReDoS safety check that rejects catastrophic patterns before execution.

Price / call$0.001

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StatusUnknown

How this service works

Test a regex against one or many inputs, safely. Send {pattern, flags?, input|inputs[], mode?}: 'match' returns the first match + capture groups, 'matchAll' every match, 'replace' the rewritten string (needs {replacement}). A mandatory ReDoS guard statically rejects catastrophic patterns (nested quantifiers, `.*.*$`, backrefs) BEFORE running — on Workers no timeout can stop a runaway regex. For agents that generate and dry-run regexes.

Output

Returns the match result according to the chosen mode: for 'match', the first match and any named or indexed capture groups; for 'matchAll', every match found across the input; for 'replace', the fully rewritten string with substitutions applied. If the pattern is detected as catastrophically backtracking (e.g. nested quantifiers, `.*.*$`, or backreferences), the request is rejected with a ReDoS safety error before any execution occurs.

Example use cases

Example prompt

“Test my regex pattern `^(\d{3})-?(\d{3})-?(\d{4})$` with the flag `i` in matchAll mode against these three strings: '555-867-5309', 'not-a-phone', and '8005551234' — and make sure it's safe to run first.”

Technical details

Endpoint

POSThttps://402utils.com/v1/regex-test?utm_source=zero.xyz

When to prefer

Choose this endpoint when an AI agent is generating or dry-running regex patterns and needs a safe execution environment — particularly when the patterns are untrusted or LLM-generated and could be catastrophically backtracking. Also ideal when you need to test a single pattern against up to 50 strings in one call, or when you need replace mode with capture group substitutions. Prefer this over running regex locally when ReDoS safety guarantees are required on a serverless/Workers runtime where timeouts cannot stop runaway patterns.

Side effects

Pattern flagged as ReDoS-unsafe — rejected before execution with a descriptive safety error
Pattern syntax error — invalid regex returns a parse error
Input string exceeds 10,000 character limit — returns a validation error
inputs array exceeds 50 items — returns a validation error
mode set to 'replace' without providing a replacement string — returns a missing-field error
Unsupported flags passed — returns a validation error

Input

Schema · Request body

Field	Type	Description
mode	string	match \| matchAll \| replace.
flags	string	Any of gimsuyd (g added automatically for matchAll).
input	string	A single input string (≤ 10000 chars).
inputs	array	Multiple input strings.
pattern	string	The regular expression source (no delimiters).
replacement	string	Replacement string (with $1, $<name>) — required for mode 'replace'.

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