mx-fiscal-mcp-server

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SAT Catalogue Lookup

sat_catalog_lookup

Read-onlyIdempotent

Find official SAT catalog entries for CFDI invoices—tax regimes, payment methods, CLABE banks, CURP states—by exact code or text search without network access.

Instructions

Look up the code tables a CFDI is written in, without downloading the SAT's spreadsheet. Nine catalogues, all bundled — this tool never touches the network.

regimen_fiscal (c_RegimenFiscal) — tax regime of issuer and receiver
uso_cfdi (c_UsoCFDI) — what the receiver does with the invoice
forma_pago (c_FormaPago) — cash, transfer, card, …
metodo_pago (c_MetodoPago) — PUE vs PPD
tipo_comprobante (c_TipoDeComprobante) — I/E/T/N/P
objeto_imp (c_ObjetoImp) — whether a line item is subject to tax (CFDI 4.0)
impuestos (c_Impuesto) — ISR / IVA / IEPS
bancos_clabe — Banxico participants by the first three CLABE digits
estados_curp — RENAPO's state keys for CURP positions 12-13

With no query you get the whole catalogue. With one, an exact code match wins (leading zeros are ignored, so '1' finds '01'); failing that it falls back to a case- and accent-insensitive substring search over both code and label, so 'confianza' finds 626 and 'oaxaca' finds OC.

Two honesty notes carried in the output: the bank list is a curated subset of Banxico's participant catalogue rather than the whole thing, and the CURP state keys are RENAPO's own — they do not match INEGI or ISO 3166-2:MX codes.

Args:

catalog (enum): one of regimen_fiscal, uso_cfdi, forma_pago, metodo_pago, tipo_comprobante, objeto_imp, impuestos, bancos_clabe, estados_curp.
query (string, optional): an exact code, or text to search for.
response_format ('markdown' | 'json'): output format (default 'markdown').

Returns: { catalog, official_name, authority, description, used_in, query, match_type, total_entries, match_count, entries[{code, label}], truncated, notes[] }.

Example: "What does UsoCFDI G03 mean?" -> sat_catalog_lookup(catalog="uso_cfdi", query="G03").

Input Schema

TableJSON Schema

Name	Required	Description	Default
`query`	No	An exact code ('626', 'G03', '012') or free text to search ('confianza', 'BBVA', 'Oaxaca'). Omit for the whole catalogue.
`catalog`	Yes	Which catalogue to read.
`response_format`	No	Output format: 'markdown' for a human-readable summary (default) or 'json' for the full structured payload.	markdown

Output Schema

TableJSON Schema

Name	Required	Description	Default
`notes`	Yes
`query`	Yes
`catalog`	Yes
`entries`	Yes
`used_in`	Yes
`authority`	Yes
`truncated`	Yes
`match_type`	Yes
`description`	Yes
`match_count`	Yes
`official_name`	Yes
`total_entries`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Sep 11, 2026

TDQS

A4.6/5.0

Behavior5/5

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

Annotations already declare the safe read-only, offline, idempotent profile, and the description reinforces it ('never touches the network'). It then adds genuinely valuable data-provenance caveats beyond the structured fields: the bank list is a curated Banxico subset, and CURP state keys deliberately do not match INEGI or ISO 3166-2:MX codes — exactly the kind of trap an agent needs warned about.

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-loads the core purpose, then uses a scannable bulleted list for the catalogues and a compact paragraph for query behavior. The catalogue glossary is long but each line earns its place; only the 'Two honesty notes carried in the output' framing is slightly padded.

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 bounded, offline lookup with a declared output schema, the description covers everything an agent needs: the enum of catalogues, query resolution rules, output format choice, provenance caveats, and a concrete example call. Nothing required to invoke it correctly is 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 baseline is 3, but the description adds matching semantics the schema omits: leading zeros are ignored ('1' finds '01') and the fallback is case- and accent-insensitive substring over both code and label. The match_type output field ties these rules to observable behavior.

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?

States a specific verb ('look up') and resource ('the code tables a CFDI is written in'), then enumerates all nine catalogues with a one-line gloss of each. This distinguishes it from siblings like validate_rfc or parse_cfdi, which validate or parse rather than resolve reference codes.

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

Usage Guidelines4/5

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

Clearly explains the two usage modes: no `query` returns the whole catalogue, a `query` does exact-then-substring matching, and it contrasts itself with 'downloading the SAT's spreadsheet' and 'never touches the network'. It stops short of explicitly naming when to reach for this over the validate_* siblings, so it is clear context rather than full alternatives guidance.

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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