Does this run entirely in my browser?

The query is composed locally but resolved by a public DNS-over-HTTPS endpoint (Cloudflare). trydevtools does not see or store your queries.

Why does an IP have no PTR record?

Reverse DNS is configured by the IP's owner, not the user. Many residential and cloud IPs have no PTR, or have a generic provider-assigned one.

How is the .arpa name built?

IPv4: reverse the octets and append .in-addr.arpa (1.2.3.4 -> 4.3.2.1.in-addr.arpa). IPv6: expand fully, reverse the nibbles, and append .ip6.arpa.

Can I trust a PTR record for identity?

Only after forward-confirming: resolve the PTR's hostname back to A/AAAA and check the original IP appears. This pattern is required for legitimate mail server verification.

ptr · rdns · doh · cloudflare · live

Reverse DNS PTR lookup

Resolve an IPv4 or IPv6 address back to its hostname via Cloudflare DNS-over-HTTPS. Everything runs in your browser.

Reverse DNS Lookup

1.1.1.1

ipv4

PTR records

answers

Status

idle

doh

ARPA

1.1.1.1.in-addr.ar…

domain

input · ip address

A reverse DNS lookup queries the PTR record of an IP's in-addr.arpa (IPv4) or ip6.arpa (IPv6) name.

ARPA form:

1.1.1.1.in-addr.arpa

Resolved via Cloudflare DNS-over-HTTPS (https://cloudflare-dns.com/dns-query).

output · ptr records

No PTR records found.

Quick Start

How a reverse DNS lookup works

An IP becomes a reversed domain under in-addr.arpa or ip6.arpa, and the PTR record at that name holds the hostname.

01
Enter an IP
IPv4 like 1.1.1.1 or IPv6 like 2606:4700::1111.
Lookups reference the IANA registries (MIME, HTTP status, TLDs) bundled at build time — no live network calls, no rate limits, no leaked queries.
inputIANAregistryofflinelive
input · queryip · IANA
```
1.1.1.1
```
loaded · IANA bundlespec · ready
02
Reverse to ARPA
Octets/nibbles are reversed and joined under in-addr.arpa or ip6.arpa.
Builders emit canonical syntax per the relevant RFC (9110 for HTTP, 5322 for headers, 3986 for URLs) so the output passes spec-compliant parsers.
arpaRFC 9110canonicalspec-compliantlive
arpa · optionsptr · live
```
1.1.1.1.in-addr.arpa
```
options applied · livecanonical
03
Query DoH
Cloudflare's DNS-over-HTTPS returns the PTR record.
Validation flags common pitfalls — uppercase header names, smart quotes inside Content-Type, missing ;charset=utf-8 — before they bite production.
dohvalidationlintpitfallslive
fetch · looked updoh · ready
```
type=PTR
```
result · livevalidated
04
Read hostname
One or more hostnames may resolve back from a single IP.
Copy writes the snippet directly into your clipboard; downloads emit the right extension and MIME so curl/httpie pick them up correctly.
resultclipboardMIME-correctblobcurl-ready
ok · copiedready · done
```
one.one.one.one
```
shipped · ready to shipsuccess

Pro tips

Web-spec details that bite later

Idempotency saves retries

POST/PUT/DELETE should be safely retried. Use idempotency keys and return the same response on duplicate requests.

Match RFC 9110 status codes

Don’t invent codes. 422 for validation errors, 409 for conflicts, 429 for rate limits. Standard codes work with off-the-shelf clients.

Set <code>Cache-Control</code> deliberately

Default browser caching is conservative. Use max-age + stale-while-revalidate for hot endpoints.

Validate Open Graph in dev

OG tags break silently. Use a previewer like OG Generator + Facebook’s debugger before launch.

CORS is a server concern

The browser sends the preflight; the server decides. Wildcard origins disable credentials — be explicit.

MIME drives behaviour

Servers must send the right Content-Type. Browsers sniff but the spec says they shouldn’t — be explicit to avoid surprises.

Use Cases

When to do reverse DNS

Spam triage, log enrichment, mail server hygiene.

Mail server hygiene

Verify your outbound IP has matching forward/reverse DNS. Bundled from IANA registries at build time — no live network call, no rate limit, no leaked queries. The MIME, TLD, and status-code tables are baked in so the tool works offline once loaded.

spec-compliant

Spam triage

Identify what's behind a hostile IP. Output is canonical per the relevant RFC (9110 for HTTP, 5322 for headers, 3986 for URLs), so spec-compliant parsers accept it as-is. Cross-browser and cross-library behaviour stays consistent.

offline

Log enrichment

Turn IPs in access logs into human-readable hostnames. Pairs with the curl-to-fetch converter for end-to-end test stubs — copy the curl from DevTools, paste, get an idiomatic fetch() body. Drop into Playwright/Vitest fixtures without manual translation.

IANA-backed

CDN debugging

Confirm an IP belongs to Cloudflare, Fastly, or your edge. Catches common pitfalls (uppercase header names, smart quotes inside Content-Type, missing ;charset=utf-8) before they bite production. Validation flags rather than auto-corrects so you stay in control.

RFC-aligned

Audit security

Spot odd hostnames that don't match expected providers. Validation runs as you type — copy only when the output is shaped correctly. The output drops directly into nginx, Apache, or CDN configs without re-formatting or re-quoting.

production-grade

Geo / ASN clues

PTR records often hint at the cloud provider and region. Same input plus same options always produces identical canonical output, so the tool is safe to embed in CI scripts that diff against expected configs.

curl-ready

FAQ

Frequently asked questions

Why are there no PTR records?

Many IPs have no PTR — it's optional. Residential and dynamic IPs often skip it; servers usually have one.

What does it mean if reverse doesn't match forward?

Forward-confirmed reverse DNS (FCrDNS) is required by many mail servers. A mismatch can cause email rejection.

Does it work for IPv6?

Yes — IPv6 addresses are expanded, nibble-reversed, and queried under ip6.arpa.

Where is the query sent?

To Cloudflare's public DoH endpoint at cloudflare-dns.com — no PII is included.

Does it run locally?

The IP-to-ARPA computation runs locally; only the DoH query leaves your browser.

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