XML Well-Formed Validator
Fix USA RSS, sitemap, and config XML in seconds. Paste like <note><to>Ada</to></note>, get well-formed valid/invalid plus root and error detail instantly offline with no signup with tag-balance entity-encoding plus declaration checks for feeds configs and integrations across publishing data and enterprise workflows daily plus CDATA guidance and envelope patterns for publishers retailers ports labs vendors and banking message flows.
Check XML documents with this XML Well-Formed Validator, catching unclosed tags, bad attributes, and encoding problems in feeds and configs.
Calculator Inputs
About XML Check
Fix USA RSS, sitemap, and config XML in seconds. Paste like <note><to>Ada</to></note>, get well-formed valid/invalid plus root and error detail instantly offline with no signup with tag-balance entity-encoding plus declaration checks for feeds configs and integrations across publishing data and enterprise workflows daily plus CDATA guidance and envelope patterns for publishers retailers ports labs vendors and banking message flows.
Native parser strict same as fetch. Parsererror surfaced with location. Valid shows root + count.
Well-formed = parseable, not schema-correct. XSD/DTD separate. Local.
Top fail: Raw & → & or CDATA. Single root required.
Privacy: No upload.
Limits: No schema validation.
Wellformed versus valid: Wellformed means parseable; valid means matching a schema too. Austin publishers fixing $200,000 RSS feeds check wellformedness first — unparseable feeds lose subscribers hourly on 09/22/2026.
Entity encoding: Ampersands and angle brackets must escape or parsers halt. Chicago retailers validating $900,000 catalogs fix bare ampersands in product names first.
Declaration headers: Mismatched encoding declarations garble international text silently. Miami ports filing manifests declare UTF-8 explicitly for accented cargo names.
Single-root rule: Exactly one root element wraps everything. Seattle vendors syncing invoices wrap batches in envelopes rather than concatenating documents.
Banking messages: New York banks exchanging $8M ISO messages reject malformed payloads instantly. Denver labs submitting assays validate before transmission windows close.
EPUB packages: Boston ebook publishers validating $300,000 EPUB containers check OPF spine XML before distributor rejection. San Francisco podcasts serving 1M feeds validate enclosure URLs weekly on 09/22/2026.
Tariff filings: Dallas airlines filing $700,000 fare tariffs validate ATPCO XML before deadlines. Atlanta logistics EDIing $4M manifests catch segment errors pre-customs.
Court e-filing: Phoenix courts e-filing $150,000 case records reject malformed submissions instantly. Philadelphia insurers exchanging $6M claims validate batches overnight.
CDATA strategy: Wrap code samples and HTML blobs in CDATA instead of escaping every bracket — readable and safe.
Where it is used
Bloggers fixing RSS feeds, SEOs validating sitemaps, devs checking API payloads, IT verifying configs, and students learning single-root rule Austin publishers fix $200,000 RSS feeds, Chicago retailers validate $900,000 catalogs, Miami ports file manifests, Denver labs submit assays, Seattle vendors sync invoices, and New York banks exchange $8M messages Boston ebooks validate $300,000 EPUB packages, San Francisco podcasts serve 1M feeds, Dallas airlines file $700,000 tariffs, Atlanta logistics EDI $4M manifests, Phoenix courts e-file $150,000 records, and Philadelphia insurers exchange $6M claims.
How to use the XML Check
- XML Document — enter the value (e.g. <note><to>Ada</to></note>).
- Calculate — press the Calculate button to see the result instantly above.
Formula
DOMParser application/xml → parsererror? invalid : valid + root tag + element count.
Examples
Valid note
Unclosed
Ampersand
Frequently Asked Questions
- Well-formed vs valid?
- Well-formed follows XML syntax rules. Valid additionally conforms to a schema (XSD/DTD). This tool checks the former.
- Why do ampersands fail?
- Raw & starts an entity reference. Escape as & (or wrap code in CDATA) — the most common XML error by far.
- Single root required?
- Yes — XML documents have exactly one root element. Fragments with siblings need a wrapper.
- Wellformed vs valid?
- Wellformed parses; valid also matches a schema. This tool checks wellformedness — pair with schema validation for contracts.
- Common failure?
- Unescaped ampersands in text content. Escape as and-amp-semicolon or wrap in CDATA sections.
- Stored anywhere?
- No. Validation runs locally in your browser. No XML is uploaded or stored.