Describe

iso8583sim.core.describe These helpers need no LLM. They power iso8583sim explain --no-llm and the MCP server’s explain_message tool.

Functions

`field_name()`

def field_name(
    field_number: int,
    network: CardNetwork | None,
    version: ISO8583Version,
) -> str

Return a field’s description, or “Unknown” if it is not defined.

`field_entries()`

def field_entries(message: ISO8583Message) -> list[dict[str, Any]]

List a message’s fields (excluding the MTI) as number, name and value entries.

`mask_pan()`

def mask_pan(pan: str) -> str

Mask a PAN, keeping the first six and last four digits.

`format_amount()`

def format_amount(amount: str, currency: str | None) -> str

Format a minor-unit amount (field 4) using the currency’s exponent, e.g. “10.00 USD”.

`decode_emv_tags()`

def decode_emv_tags(data: str) -> list[dict[str, Any]]

Decode EMV TLV data into named tags, explaining the TVR (95) and CID (9F27).

`describe_mti()`

def describe_mti(mti: str) -> dict[str, str]

Describe an MTI’s message class, function and origin.

`describe_message()`

def describe_message(message: ISO8583Message) -> dict[str, Any]

Describe a message in plain language without an LLM. Parameters

ISO8583Message

required

Parsed message

dict[str, Any]

Dictionary with a one-paragraph “summary”, the MTI breakdown, named fields

dict[str, Any]

and, when field 55 is present, decoded EMV tags

Core

Security

Wire formats

Networking

LLM

Servers

Demo

Functions

`field_name()`

`field_entries()`

`mask_pan()`

`format_amount()`

`decode_emv_tags()`

`describe_mti()`

`describe_message()`

​Functions

​field_name()

​field_entries()

​mask_pan()

​format_amount()

​decode_emv_tags()

​describe_mti()

​describe_message()

Functions

`field_name()`

`field_entries()`

`mask_pan()`

`format_amount()`

`decode_emv_tags()`

`describe_mti()`

`describe_message()`