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InvoiceIn

by io.github.peculiar-systems
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Validate invoice

validate_invoice
Read-onlyIdempotent

Validate one European or UAE (PINT AE) e-invoice against the official rule sets (XSD, EN 16931, XRechnung, Peppol BIS, PINT AE, FatturaPA, KSeF, arithmetic) and return the verdict without the invoice body. Use it for pass/fail and the list of errors and warnings; use read_invoice when you also need lines, totals and payment data. Input: XML (UBL, CII, XRechnung, Peppol BIS 3, UAE PINT AE, FatturaPA, KSeF FA(2)/FA(3)) or a ZUGFeRD/Factur-X hybrid PDF up to 25 MB; plain or scanned PDFs without embedded XML are rejected (no OCR). Returns the validation report (valid flag, counts, rule sets with versions, failed rules with rule id, severity, fix hint in lang, affected field and who must act), the detected source and the document header; an unreadable file returns ok=false with error.code/message/hint instead of raising. For a Polish KSeF invoice, a KSeF number passed in ksef is checked too: shape, NIP check digit, and agreement with the invoice it came with. Costs one invoice credit per call; without an API key the anonymous quota is 20 invoices per day per IP. Nothing is stored.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
ksefNoPoland only: the KSeF number the National e-Invoice System gave this invoice — 35 characters, NNNNNNNNNN-RRRRMMDD-FFFFFFFFFFFF-FF — or the collective identifier covering it (NNNNNNNNNN-IZRRRRMM-FFFFFFFFFFFF-FF). KSeF assigns it on acceptance, so it is never inside the FA(2)/FA(3) XML: it arrives beside the invoice in the KSeF API response, the UPO or the QR code on a visualisation. Pass it and it is checked against the invoice and returned on payment.ksef_number, the reference a Polish buyer must quote in the bank transfer title from 2027-01-01. Leave empty for invoices from any other country.
langNoLanguage of the fix hints in the validation report and of the labels in HTML output. Default en.en
pathNoAbsolute path of the invoice file on the machine running the server, used instead of file_base64. Only honoured over stdio (`python -m invoicein.mcp_server`); the hosted server at invoicein-api.peculiar.systems ignores it and answers with an error asking for file_base64.
file_base64NoInvoice file content, base64-encoded (standard alphabet). Accepted content: XML in UBL 2.1, CII D16B, XRechnung, Peppol BIS Billing 3, FatturaPA 1.2 or KSeF FA(2)/FA(3) syntax, or a ZUGFeRD 1.0/2.x or Factur-X hybrid PDF (the embedded XML is used). Max 25 MB decoded. Required unless `path` is given.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
okYesFalse when the file could not be read; then only `error` is set
errorNoPresent when ok is false: code, message, hint
sourceNoDetected syntax, format, profile and container
documentNoInvoice header: id, issue_date, type_code, currency, due_date …
validationNo

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changed
    • addedInput schema / properties / ksef
      Added value: +{
+  "default": "",
+  "description": "Poland only: the KSeF number the National e-Invoice System gave this invoice — 35 characters, NNNNNNNNNN-RRRRMMDD-FFFFFFFFFFFF-FF — or the collective identifier covering it (NNNNNNNNNN-IZRRRRMM-FFFFFFFFFFFF-FF). KSeF assigns it on acceptance, so it is never inside the FA(2)/FA(3) XML: it arrives beside the invoice in the KSeF API response, the UPO or the QR code on a visualisation. Pass it and it is checked against the invoice and returned on payment.ksef_number, the reference a Polish buyer must quote in the bank transfer title from 2027-01-01. Leave empty for invoices from any other country.",
+  "title": "Ksef",
+  "type": "string"
+}
  2. Changed21 schema fields changed
    • removedInput schema / properties / file_base64 / anyOf
      Removed value: -[
-  {
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]
    • changedInput schema / properties / file_base64 / default
      Previous value: -nullNew value: +""
    • changedInput schema / properties / file_base64 / description
      Previous value: -"The invoice file, base64-encoded: XML (UBL, CII, XRechnung, Peppol, FatturaPA, KSeF FA(3)) or a ZUGFeRD/Factur-X hybrid PDF. Up to 25 MB decoded."New value: +"Invoice file content, base64-encoded (standard alphabet). Accepted content: XML in UBL 2.1, CII D16B, XRechnung, Peppol BIS Billing 3, FatturaPA 1.2 or KSeF FA(2)/FA(3) syntax, or a ZUGFeRD 1.0/2.x or Factur-X hybrid PDF (the embedded XML is used). Max 25 MB decoded. Required unless `path` is given."
    • addedInput schema / properties / file_base64 / type
      Added value: +"string"
    • changedInput schema / properties / lang / description
      Previous value: -"Language of the fix hints and rendering labels: en, de, pl, it or fr."New value: +"Language of the fix hints in the validation report and of the labels in HTML output. Default en."
    • addedInput schema / properties / lang / enum
      Added value: +[
+  "en",
+  "de",
+  "pl",
+  "it",
+  "fr"
+]
    • removedInput schema / properties / lang / pattern
      Removed value: -"^(en|de|pl|it|fr)$"
    • removedInput schema / properties / path / anyOf
      Removed value: -[
-  {
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]
    • changedInput schema / properties / path / default
      Previous value: -nullNew value: +""
    • changedInput schema / properties / path / description
      Previous value: -"Local file path instead of file_base64; only honoured when the server runs over stdio on the same machine."New value: +"Absolute path of the invoice file on the machine running the server, used instead of file_base64. Only honoured over stdio (`python -m invoicein.mcp_server`); the hosted server at invoicein-api.peculiar.systems ignores it and answers with an error asking for file_base64."
    • addedInput schema / properties / path / type
      Added value: +"string"
    • addedOutput schema / $defs / Validation / properties / errors / description
      Added value: +"Number of failed rules with severity error"
    • addedOutput schema / $defs / Validation / properties / issues / description
      Added value: +"Failed rules, each with a fix hint"
    • addedOutput schema / $defs / Validation / properties / notes / description
      Added value: +"Informational notes about the validation run"
    • changedOutput schema / $defs / Validation / properties / rule_sets / description
      Previous value: -"Rule sets applied, with versions"New value: +"Rule sets applied, with versions (XSD, EN 16931, XRechnung, Peppol, FatturaPA, KSeF, arithmetic)"
    • addedOutput schema / $defs / Validation / properties / valid / description
      Added value: +"True when no rule of severity error failed"
    • addedOutput schema / $defs / Validation / properties / warnings / description
      Added value: +"Number of failed rules with severity warning"
    • changedOutput schema / properties / document / description
      Previous value: -"Invoice header: id, issue_date, currency, due_date …"New value: +"Invoice header: id, issue_date, type_code, currency, due_date …"
    • addedOutput schema / properties / error / description
      Added value: +"Present when ok is false: code, message, hint"
    • addedOutput schema / properties / ok / description
      Added value: +"False when the file could not be read; then only `error` is set"
    • addedOutput schema / properties / source / description
      Added value: +"Detected syntax, format, profile and container"
  3. First observed

TDQS

A4.8/5.0
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The annotations already indicate read-only, idempotent, non-destructive behavior. The description adds meaningful context beyond those hints: unreadable files return ok=false instead of raising an exception, nothing is stored, one invoice credit is consumed per call, and the anonymous quota is 20 invoices per day per IP. No contradictions with annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is long but well-organized, front-loading purpose and usage, then covering return values, input constraints, KSeF specifics, and operational details like credits and storage. Some redundancy with the extensive schema descriptions exists, but every sentence contributes useful context for a complex validation tool.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a complex tool with an output schema, the description covers all essential operational aspects: accepted inputs, file size limit, error behavior, KSeF handling, cost/quota, storage, and when to choose a sibling tool. Nothing needed for correct invocation appears to be missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3. The description adds real value by explaining how the ksef parameter is validated against the invoice and returned on payment.ksef_number, and by clarifying that path is only honoured over stdio while the hosted server ignores it. This goes beyond the schema's already-detailed field descriptions.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource: 'Validate one European or UAE (PINT AE) e-invoice against the official rule sets' and 'return the verdict without the invoice body.' It distinguishes itself from read_invoice by explicitly noting that read_invoice is for when lines, totals and payment data are also needed.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides explicit when-to-use guidance: 'Use it for pass/fail and the list of errors and warnings; use read_invoice when you also need lines, totals and payment data.' It also clarifies input boundaries, including accepted XML/PDF formats and rejection of plain or scanned PDFs without embedded XML.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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