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

Data Types

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

Logical Type	dataTypes value	Example value	How to convert
String	`STRING`	`"Canada-Dollar"`	No conversion needed
Number	`NUMBER`	`"36123456789012.34"`	`float(value)`
Date	`DATE`	`"2024-03-31"`	`pd.to_datetime(value)`
Currency	`CURRENCY`	`"1234567.89"`	`float(value)`
Integer	`INTEGER`	`"42"`	`int(value)`
Percentage	`PERCENTAGE`	`"4.25"`	`float(value)`

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

Data Registry

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

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