# Source citation standards [#source-citation-standards]

Use this page when you add or review tax facts, rules, parameter tables,
calculators or incorrect-result fixes.

## Required citation details [#required-citation-details]

Each source citation should include:

* publisher or authority
* document title
* section, schedule, table or page range
* URL or stable reference
* access date
* effective period or tax year
* the rule, parameter or fact that uses the source

Prefer official sources. If you use a secondary source for context, explain
which official source proves the implemented behaviour.

## Parameter periods [#parameter-periods]

Parameter descriptors must include source references and effective periods.
When a table supports a tax year, the descriptor should make overlap and
period review possible.

```txt
source citation
  -> parameter descriptor
  -> effective period
  -> rule descriptor
  -> trace and graph metadata
```

## Pull request notes [#pull-request-notes]

In your PR, group source citations beside the changed facts, rules,
calculators or tax years. Add a short note when a source changes public API,
SDK, report, trace or ledger behaviour.

For deeper rules, read
[Rules and parameters](https://github.com/crcorbett/taxkit/blob/a151e51e8a30247526fa93412df046955846eca4/docs/architecture/rules-and-parameters.md)
and
[Graph, trace and ledgers](https://github.com/crcorbett/taxkit/blob/a151e51e8a30247526fa93412df046955846eca4/docs/architecture/graph-trace-ledgers.md).