A bond yield fluctuation API returns how a 10Y (or other tenor) moved between two dates: start_yield, end_yield, change, change_pct, plus min/max. On Bonds-API that is GET https://bonds-api.com/api/v1/fluctuation with query api_key. Official docs sample is dated 2026-04-14.
Starter is $19/mo (1,000 requests) with a 7-day trial. Pro is $49 / 10k. This is not Fed Funds / SOFR (Interest Rates API). Docs: bonds-api.com/docs (fluctuation).
Request: 10Y over a range
curl "https://bonds-api.com/api/v1/fluctuation?api_key=YOUR_API_KEY&countries=US,TR,EG&maturity=10Y&start=2026-04-01&end=2026-04-14"
Docs example query uses countries=US,TR,EG. The printed JSON body shows IT and GR — copy the live object for the countries you send.
Response: official fluctuation sample
{
"success": true,
"maturity": "10Y",
"fluctuations": {
"IT": {
"start_yield": 3.52,
"end_yield": 3.68,
"change": 0.16,
"change_pct": 4.55,
"min": 3.21,
"max": 3.95
},
"GR": {
"start_yield": 3.15,
"end_yield": 3.31,
"change": 0.16,
"change_pct": 5.08,
"min": 2.98,
"max": 3.62
}
},
"meta": {
"request_id": "3efeeaa7-d4ab-4cde-8104-78fd402052a9",
"timestamp": "2026-04-14T09:00:00Z"
}
}
Same key
GET /api/v1/latest?countries=IT&maturities=10Y— spotIT_10Y.GET /api/v1/spread?country=IT&benchmark=DE&maturity=10Y— Italy–Germany spread.GET /api/v1/curve?country=US— full Treasury curve.
MCP: mcp.bonds-api.com.
