Free Index Data API
Sources, Limits & Python

Define the exact index series before choosing an API

The request must identify the exact index family, version, currency, and return convention. A price index, gross total-return index, net total-return index, hedged version, and real-time calculated variant can share a familiar name while producing different levels and histories. Store the publisher's stable identifier and methodology version, not only a display symbol.

A practical integration usually starts with a documented S&P 500 or global index identifier, then retrieves a latest level or historical OHLC series in consistent JSON or CSV for a dashboard, research notebook, or agent. The endpoint must expose enough reference metadata to prove that the requested and returned series are the same index variant.

Coverage a stock index data API should provide

Free market index API sources to evaluate

Use a fixed benchmark set rather than a single famous symbol: one domestic equity price index, its total-return sibling, an international index, a currency-converted or hedged version, and one rebalance date. Compare identifiers, level and OHLC definitions, calendars, return treatment, delay, status, revision, constituent availability, and license.

Use the table as a verification checklist rather than an endorsement. Endpoint access, symbol coverage, delay, and licensing can change, so confirm every required series against the provider's current documentation and a known observation date.

Validate index returns, rebalances, and corporate actions

Worked return example: price and total-return indices answer different questions

Assume a price index starts at 1,000 and finishes the year at 1,080. Its price return is 8%. If constituent distributions add 25 index points when reinvested under the methodology, a comparable gross total-return index would end near 1,105, or 10.5% above the start. A net total-return version may finish lower after its stated withholding-tax assumptions.

The levels are illustrative, but the rule is operational: never splice a price series to a total-return series, and never infer dividend income by subtracting two indices unless publisher, base date, currency, calendar, tax convention, and methodology are compatible. Store the exact series identifier with every observation.

Worked rebalance timeline: announcement is not effective membership

Suppose a provider announces an addition on June 5, determines reference weights using June 14 data, publishes final weights on June 19, and makes the change effective after the June 21 close. A point-in-time constituent query for June 10 should keep the old membership while separately exposing the pending announcement. A portfolio tracking the index normally applies the new membership at the methodology's stated effective moment—not retroactively on June 5.

Keep announcement, reference, publication, implementation, and first-trading dates as separate fields. Historical research should use the information available by the simulated decision time and include deletions, suspended securities, and identifier changes. Using today's constituent list for earlier dates creates both look-ahead and survivorship bias.

Corporate actions can preserve economics while changing raw fields

Index data API Python example and validation

Normalize the provider response first, then validate the exact series identity together with its values. This example rejects a response that silently changes publisher, index variant, currency, or return treatment even when the display symbol looks unchanged.

from datetime import datetime
from decimal import Decimal, InvalidOperation


def parse_time(value: str) -> datetime:
    parsed = datetime.fromisoformat(value.replace("Z", "+00:00"))
    if parsed.tzinfo is None:
        raise ValueError("index timestamp must include a timezone")
    return parsed


def validate_index_history(payload: dict, expected: dict) -> list[dict]:
    identity = ("publisher", "index_id", "variant", "currency", "return_type")
    mismatched = [key for key in identity if payload.get(key) != expected.get(key)]
    if mismatched:
        raise ValueError(f"unexpected index series: {mismatched}")
    if payload.get("status") not in {"official", "corrected"}:
        raise ValueError("history is not an official or corrected series")

    rows = []
    previous_time = None
    for raw in payload.get("values", []):
        timestamp = parse_time(raw["timestamp"])
        try:
            opening = Decimal(str(raw["open"]))
            high = Decimal(str(raw["high"]))
            low = Decimal(str(raw["low"]))
            close = Decimal(str(raw["close"]))
        except (KeyError, InvalidOperation) as exc:
            raise ValueError("invalid index OHLC row") from exc
        if min(opening, high, low, close) <= 0:
            raise ValueError("index levels must be positive")
        if high < max(opening, close) or low > min(opening, close) or high < low:
            raise ValueError(f"impossible OHLC at {timestamp.isoformat()}")
        if previous_time is not None and timestamp <= previous_time:
            raise ValueError("index history must be strictly increasing")
        rows.append({"timestamp": timestamp, "open": opening,
                     "high": high, "low": low, "close": close})
        previous_time = timestamp
    if not rows:
        raise ValueError("response contains no index observations")
    return rows

How QVeris helps connect index data capabilities

• Search separately for index levels, historical series, constituents, weights, and methodology or reference data.
• Require publisher, exact index variant, currency, return treatment, interval, date range, freshness, status, and entitlement in the capability request.
• Preserve provider IDs, source timestamps, revision state, methodology version, and license with every downstream result.

• Open the QVeris provider details for relevant financial-data capabilities.
• Inspect inputs, outputs, authentication, provider documentation, and supported index identifiers before connecting.
• Keep provider, effective date, retrieval time, and license notes with each result; QVeris connectivity is not investment advice.

Free index data API FAQ

Authoritative references