TL;DR: There is no single "best" market data API for AI, only the best for your job. Want raw real-time prices? Look at dedicated market-data vendors. Want fundamentals? Different tools shine. Want an agent to query in plain language with every number traced to its source? That is where an MCP-native, provenance-first layer fits. Here is how the landscape breaks down.

First, decide what you actually need

Real-time prices / quotes / options — high-frequency, low-latency feeds.
Fundamentals — income statements, balance sheets, ratios.
Ownership & filings — who holds what (13F, insider trades).
Agent-native access — an MCP server so Claude/ChatGPT can call it directly.
Provenance — every datapoint traced to a primary source (matters when an agent is citing numbers).

The landscape (honest, by use case)

Tool	Strongest for	Notes
Polygon.io	real-time + historical US stocks/options/crypto	developer-focused price data; you wire the REST/websocket yourself
Alpha Vantage	free-tier prices, FX, crypto, simple indicators	generous free tier; great for prototypes, rate-limited
Financial Modeling Prep	fundamentals & financial statements	good for company financials and ratios
Arkolith	agent-native real-world + ownership data, MCP-native	one key for markets, filings (13F live), the physical economy; provenance on every datapoint

(Characterizations are general; check each vendor's current docs for specifics.)

The axis most comparisons miss: agent-native + provenance

Most market-data APIs were built for code, not agents. If you're putting data in front of an LLM, two things matter that price-feed benchmarks ignore:

Can the agent call it directly? An MCP server means the agent discovers tools and queries in plain language, no glue code. (See MCP vs REST API.)
Can it cite the number? If every datapoint carries its source and timestamp, the agent answers with evidence instead of a confident guess. (See How to stop your AI hallucinating numbers.)

That's the gap Arkolith is built for: not the cheapest tick data, but the easiest, most-sourced way for an agent to reach real-world financial data.

How to choose

Building a trading dashboard in code? A dedicated price-feed vendor.
Need company fundamentals? A fundamentals API.
Want your agent to answer real-world-economy questions with sourced data, via one key? That's the MCP-native lane.

Frequently asked questions

Which market data API is best for an AI agent specifically?

The one your agent can call directly (MCP-native) and whose data it can cite (provenance). Raw latency matters less when an LLM is the consumer.

Can I use more than one?

Yes, many teams combine a price feed with an ownership/filings source. The value is in the joins.

Arkolith is the MCP-native, provenance-first option. Get a key or read the docs.