Rexact
NPM · REXACT-MCP
Verify, explain and audit regexes (ReDoS, engine compatibility) offline.
Available components
Last scanned (5 hours ago)
Scores higher than 39% of npm servers
Category Developer Tools
How this component scores in each security and reliability category. Every signal is checked automatically from public evidence about the published package, including repeated runs of it in an isolated sandbox, and we only credit what we can confirm. How we score → Why this is hard to score →
Supply Chain Security98
- No malware found by supply-chain analysis.Pass
- No known CVEs affecting this package version or its production dependencies.Pass
- No install/post-install scripts declared.Pass
- 31 of 103 dependencies flagged as unhealthy. View diagnostics → Partial
Provenance & Transparency45
- Source repository is publicly reachable at the declared URL. View diagnostics → Pass
- Provenance check failed: no build-provenance attestation is published. See how to fix → View diagnostics → Fail
- Clear OSI-approved license (MIT).Pass
- Actively maintained (last published 1 days ago).Pass
- Disclosure check failed: no security disclosure policy was found in the source repository. See how to fix → Fail
Schema Quality & AI Usability74
- AI-judged instruction clarity (good).Pass
- Tool/resource definitions use about 502 tokens (~100/item across 5 items; 5 tools + 0 resources), lean.Pass
- Usage-examples check failed: none of the tools include examples. See how to fix → Fail
Stability & Change Management0
- Stability not yet verified: not enough scan history yet (needs a 30-day window).Unverified
Tool Coverage100
- 100% of tools have a non-trivial description (not blank, and not just the tool's name).Pass
- 100% of tool parameters carry a description.Pass
- Structured output schemas are declared (100% of tools); any adoption earns full credit.Pass
Tool Safety100
- No prompt-injection markers were found in the server instructions, tool names or descriptions we captured.Pass
- We read all 5 captured tool definition(s), and no name or description among them implies an irreversible operation.Pass
- An AI judge read all 5 captured unit(s) of tool text and found none that tries to manipulate the model reading it.Pass
Capabilities100
- Implements a supported MCP spec version (2025-11-25); the latest is 2026-07-28.Pass
Unverified: 1 category
A category scored 0 because we could not verify it: a data source with nothing on this package, evidence we could not reach, or a check we could not run. We only credit what we can confirm.
Every change we have recorded for this component, newest first. Security-relevant changes are always shown. ▲ marks a change for the better, ▼ a change for the worse; unmarked changes are neutral.
- 16 Oct 26 +15
- Malware scan: unverified → pass ▲ security
- 15 Oct 26 55
First indexed and scored.
Diagnostic detail from the automated scan of this channel: what the scanner observed at each step, so you can see exactly where a check passed or failed. It is informational only and never changes the trust score.
Captured 17 Oct 2026 · Analysed npm/rexact-mcp@0.1.2
Provenance No attestation
The registry publishes no build provenance for this version, so there is nothing to verify.
| Result | No attestation |
|---|---|
| Ecosystem | npm |
Background: How many MCP packages publish verified provenance →
Dependencies 103 packages
| Packages resolved | 103 |
|---|---|
| Stale | 31 |
| Tree resolution | Complete |
Background: SBOMs and build attestations, explained →
The tools this component advertises to a client, with an estimated token cost for each. Expand a tool to see its parameters and schema. The per-tool counts are indicative and are not scored directly; the schema's total context footprint is one signal in Schema Quality & AI Usability. A tool's description is untrusted text the model reads on every call, which is what makes this list a security surface and not just an inventory: how tool poisoning works →
check_compat Check cross-engine regex compatibility ~141
Reports syntax and semantic differences when a pattern is ported from its source flavor to one or more target engines (PCRE, RE2, Python, Java, .NET, POSIX grep). Offline, no API key required.
| Name | Type | Req | Description |
|---|---|---|---|
| flags | string | – | JavaScript regex flags, e.g. "gi". |
| pattern | string | yes | The regex source, without delimiters. |
| sourceFlavor | string | – | The flavor the pattern was authored for. Not in SPEC-TECHNIQUE.md's input list for this tool — added because checkCompat() requires it; defaults to "js". |
| targets | array | yes | Engines to check compatibility against. |
| Name | Type | Req | Description |
|---|---|---|---|
| issues | array | yes | – |
No examples provided.
check_redos Check a regex for catastrophic backtracking (ReDoS) ~70
Statically and dynamically analyzes a pattern for ReDoS risk — never executes it against user-supplied input. Offline, no API key required.
| Name | Type | Req | Description |
|---|---|---|---|
| flags | string | – | JavaScript regex flags, e.g. "gi". |
| pattern | string | yes | The regex source, without delimiters. |
| Name | Type | Req | Description |
|---|---|---|---|
| attackString | string | – | – |
| complexity | string | – | – |
| hotspot | array | – | – |
| maxSteps | number | – | – |
| status | string | yes | – |
No examples provided.
explain_regex Explain a regex token by token ~86
Breaks a pattern down into an ordered list of tokens (anchors, groups, quantifiers...) with a plain-language explanation for each. Offline, no API key required.
| Name | Type | Req | Description |
|---|---|---|---|
| flags | string | – | JavaScript regex flags, e.g. "gi". |
| locale | string | – | Language for the plain-text explanation. |
| pattern | string | yes | The regex source, without delimiters. |
| Name | Type | Req | Description |
|---|---|---|---|
| tokens | array | yes | – |
No examples provided.
generate_regex Generate a regex from a natural-language description ~115
Asks an LLM to draft a pattern from a description and test cases, then deterministically verifies it (compile, corpus, ReDoS) before returning it — never returns unverified model output. Requires ANTHROPIC_API_KEY in the MCP server's own environment (your own key, your own cost).
| Name | Type | Req | Description |
|---|---|---|---|
| cases | array | yes | Test cases the generated pattern must satisfy. |
| description | string | yes | Natural-language description of the pattern to generate. |
| flavor | string | yes | Target regex flavor for the generated pattern. |
| Name | Type | Req | Description |
|---|---|---|---|
| attempts | number | yes | – |
| explanation | array | yes | – |
| flags | string | yes | – |
| flavor | string | yes | – |
| pattern | string | yes | – |
| redos | object | yes | – |
| report | object | yes | – |
No examples provided.
verify_regex Verify a regex against test cases ~90
Runs a regular expression against a set of test cases in a sandboxed worker (never on the calling process) and returns a pass/fail report. Offline, no API key required.
| Name | Type | Req | Description |
|---|---|---|---|
| cases | array | yes | Test cases to run the pattern against. |
| flags | string | – | JavaScript regex flags, e.g. "gi". |
| pattern | string | yes | The regex source, without delimiters. |
| Name | Type | Req | Description |
|---|---|---|---|
| durationMs | number | yes | – |
| passed | number | yes | – |
| results | array | yes | – |
| total | number | yes | – |
No examples provided.
How do I install the Rexact MCP server?
Rexact runs locally as an npm package, launched with npx -y rexact-mcp. Ready-made configuration for Claude, Cursor, VS Code, Codex and 5 more is on this page, copied from each client's own documentation.
npm · rexact-mcp
claude mcp add nicolasmar91-rexact-mcp -- npx -y rexact-mcp
What is the Rexact MCP server?
Rexact is an MCP server listed in the public MCP registry as io.github.Nicolasmar91/rexact-mcp. Verify, explain and audit regexes (ReDoS, engine compatibility) offline. This page covers its npm package (rexact-mcp).
Is the Rexact MCP server safe to use?
Rexact scores 70 out of 100 on VerifyMCP. We found no known CVEs affecting it as of 17 October 2026. It declares no install or post-install scripts. That is a record of what we were able to check automatically, not an endorsement. The category breakdown on this page shows every signal behind the number, including the ones we could not confirm.
What tools does the Rexact MCP server expose?
Rexact exposes 5 tools: verify_regex, check_redos, explain_regex, check_compat, generate_regex. Their descriptions and schemas cost roughly 502 tokens of context every time the server is loaded.
Is the Rexact MCP server still maintained?
Rexact is still listed as active in the MCP registry. We last reached this channel on 17 October 2026. Those dates come from our own scans of the registry and the channel itself, not from anything the publisher announced.
What licence is the Rexact MCP server under?
Rexact declares the MIT licence, which is OSI-approved. That covers the source only, and says nothing about the cost of any service it calls.