InvoiceIn

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

Name	Required	Description	Default
`ksef`	No	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.
`lang`	No	Language of the fix hints in the validation report and of the labels in HTML output. Default en.	en
`path`	No	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.
`file_base64`	No	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.

Output Schema

TableJSON Schema

Name	Required	Description
`ok`	Yes	False when the file could not be read; then only `error` is set
`error`	No	Present when ok is false: code, message, hint
`source`	No	Detected syntax, format, profile and container
`document`	No	Invoice header: id, issue_date, type_code, currency, due_date …
`validation`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 17, 2026

addedOutput schema / $defs / Validation / properties / coverage

Added value: +{
+  "anyOf": [
+    {
+      "type": "string"
+    },
+    {
+      "type": "null"
+    }
+  ],
+  "default": "rules",
+  "description": "'rules' when the business-rule sets ran and `valid` is a verdict; 'schema' when only XSD and arithmetic could run (profile below EN 16931, ZUGFeRD 1.0, FatturaPA, KSeF, unsupported PINT jurisdiction, or Schematron skipped for size) — then valid=true means 'nothing we could check failed', not 'conforms'",
+  "title": "Coverage"
+}

Changed1 schema field changedSep 11, 2026

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"
+}

Changed21 schema fields changedSep 8, 2026

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"

First observedSep 7, 2026

TDQS

A4.6/5.0

Behavior5/5

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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds material context beyond them: one invoice credit per call, anonymous quota of 20 per day per IP, 'nothing is stored', the 25 MB cap, and the error contract (ok=false with error.code/message/hint instead of raising). That is exactly the operational detail an agent needs for a read-only tool with quota costs.

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?

Front-loaded with purpose, then routing to the alternative, then inputs, return shape, and cost model — a sensible ordering with little waste. It is dense though: the return-value sentence packs a long parenthetical list of report fields that could be tightened.

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?

With annotations covering the safety profile and an output schema plus a full-coverage input schema, the description only needs to add routing, limits, and failure semantics — and it does all three. Nothing an agent needs in order to call this correctly is missing.

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

Parameters3/5

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

Schema description coverage is 100%, so each of the four parameters is already fully documented in the schema, including the ksef identifier format and the stdio-only behaviour of `path`. The description restates the accepted input formats and the ksef cross-check but adds no syntax or constraint beyond the schema, so the baseline 3 applies.

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?

Names a specific verb (validate) and resource (one European or UAE PINT AE e-invoice) and enumerates the actual rule sets applied (XSD, EN 16931, XRechnung, Peppol BIS, PINT AE, FatturaPA, KSeF, arithmetic). It also explicitly distinguishes itself from the sibling read_invoice, so an agent can route without opening either schema.

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?

Gives an explicit when-to-use ('use it for pass/fail and the list of errors and warnings') and names the alternative with the selecting condition ('use read_invoice when you also need lines, totals and payment data'). It also states a negative case (plain or scanned PDFs without embedded XML are rejected, no OCR), covering when the tool will refuse.

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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