6502 API


The purpose of the API is to serve as an instruction set reference for the MOS 6502. It returns JSON objects when queried, and returns nothing if the specified instruction or instruction/addressing mode combo cannot be found. The fact number uses a modulus and so querying for a specific fact number will always return something.

The API can be accessed at http://rlannon.heroku.com/api/v1/6502/<path here> from any domain. The API should typically be accessed with GET requests, but a few paths support POST requests as well, one for accessing data and one for updating the database. Currently, the application does not require authentication or an API key. Please use it responsibly.


Path Description
/instructions Returns a list of all instructions. Supports HTTP POST requests for fetching JSON data as well. The form that is submitted must have inputs with the names mnemonic and addressing_mode; the former is required and must be all caps, the latter is optional
/instructions/<mnemonic> Return all information for a specific instruction
/instructions/<mnemonic>/<addressing mode> Returns the opcode, instruction length, and execution time for an instruction with the given addressing mode
/flags Returns information about all processor flags
/flags/<flag> Returns information about the specified flag
/facts Returns a list of facts about the 6502
/fact Returns a random fact from our list
/fact/<number> Returns a specific fact
/facts/add Supports HTTP POST requests for adding a fact to the database. Form must have an input with the name fact or the request will be ignored


The mnemonic should be the 3-letter instruction mnemonic in caps. The available addressing modes are:

Code Addressing mode
imm Immediate addressing
zp Zero page
zp,x Zero page, X
zp,y Zero page, Y
abs Absolute
abs,x Absolute, X
abs,y Absolute, Y
ind Indirect
ind,x Indirect, X (indexed indirect)
ind,y Indirect, Y (indirect indexed)
a A register
impl Implied

The flag should be followed by a char with the flag identifier: * N - Negative * V - Overflow * B - Break * D - Decimal * I - Interrupt disable * Z - Zero * C - Carry

Returned Information

Mnemonic alone

Information returned about instructions includes:

Field Description
mnemonic The 3-letter mnemonic for the instruction
name The name of the instruction
description A brief description of the instruction
flags The flags affected by the instruction

Mnemonic with addressing mode

Information returned about specific isntructions includes:

Field Description
mnemonic The 3-letter mnemonic for the instruction
addressing_mode The addressing mode (see above for codes)
opcode The opcode for the instruction
length The length of the instruction (in bytes)
time The number of cycles it takes to execute the instruction
page_boundary_increase Whether the execution time increases when a page boundary is crossed


Fact information returns a string fact containing the fact.


Flags information returns:

Field Description
flag A char with the flag identifier
name The name of the flag
description The description of the flag and its use