API Basics — U.S. Treasury Fiscal Data

Overview

• RESTful API — accepts HTTP GET requests only
• Returns JSON by default (also CSV, XML)
• No API key, no authentication, no registration required
• Open data, free for commercial and non-commercial use
• Current versions: v1 and v2 (check each dataset's page for which version applies)

URL Structure

BASE URL + ENDPOINT + PARAMETERS

Base URL:  https://api.fiscaldata.treasury.gov/services/api/fiscal_service
Endpoint:  /v2/accounting/od/debt_to_penny
Params:    ?fields=record_date,tot_pub_debt_out_amt&sort=-record_date&page[size]=5

Full URL:
https://api.fiscaldata.treasury.gov/services/api/fiscal_service/v2/accounting/od/debt_to_penny?fields=record_date,tot_pub_debt_out_amt&sort=-record_date&page[size]=5

• Endpoint components use lowercase + underscores
• Endpoint names are singular

API Versioning

• v1: Earlier datasets (DTS, MTS, some debt tables)
• v2: Newer or updated datasets (Debt to Penny, TROR, avg interest rates)
• Check the specific dataset page at fiscaldata.treasury.gov/datasets/ to confirm the version

Verifying Endpoint Paths

Endpoint paths change when datasets are restructured. Always confirm the current path on the dataset's API Quick Guide before querying.

Authoritative sources (in order):

1. Dataset detail page at https://fiscaldata.treasury.gov/datasets/{slug}/
2. Gatsby page data: https://fiscaldata.treasury.gov/page-data/datasets/{slug}/page-data.json (look for "endpoint" fields)
3. API endpoint table

Data Types

All field values in responses are strings (quoted), regardless of their logical type.

Null values appear as the string "null" (not Python None or JSON null).

# Safe numeric conversion handling nulls
def safe_float(val):
    return float(val) if val and val != "null" else None

HTTP Methods

• Only GET is supported
• POST, PUT, DELETE return HTTP 405

Rate Limiting

• HTTP 429 is returned when rate limited
• No documented fixed rate limit; implement retry with backoff for bulk requests

import time
import requests

def get_with_retry(url, params, retries=3):
    for attempt in range(retries):
        resp = requests.get(url, params=params)
        if resp.status_code == 429:
            time.sleep(2 ** attempt)
            continue
        resp.raise_for_status()
        return resp.json()
    raise Exception("Rate limited after retries")

Caching

• HTTP 304 (Not Modified) can be returned for cached responses
• Safe to cache responses; most datasets update daily, monthly, or quarterly

Pagination Headers

Responses include pagination in two places:

• links object in the JSON body (self, first, prev, next, last)
• Link HTTP header with RFC 5988 relations (rel="first", rel="next", etc.)

Either can be used to navigate pages programmatically. See response-format.md for details.

Data Registry

The Fiscal Service Data Registry contains field definitions, authoritative sources, data types, and formats across federal government data.