Head to head · Market prices · October 2026 research run

Finnhub vs Massive (formerly Polygon.io)

Massive (formerly Polygon.io) scores 73.1 (BB) on agent readiness against Finnhub's 45.1 (E), and leads in every scored category. Both do market prices. Massive (formerly Polygon.io) accepts x402. Finnhub doesn't.

Best financial market data APIs for AI agents · All 55 markets comparisons

Which one, for what

Finnhub E

Best for Agents that need one key across quotes, fundamentals, estimates, filings and transcripts with official libraries, and a free key for prototypes.

Also in its favour

  • Free to start without a card

Watch for

The Swagger document declares the key only as a token query parameter, and the examples carry it in the URL

Massive (formerly Polygon.io) BB

Best for Agents that need US equities, options or futures data with real history, and the only listing here selling US stock data over x402.

Ahead on

  • Reliability, 78 against 48
  • Schema & documentation, 89 against 58
  • Agent ergonomics, 78 against 56
  • Payments & pricing, 90 against 30
  • Maintenance & community, 82 against 60
  • Transparency & trust, 67 against 27

Also in its favour

  • Agent-ready, a grade of BB or better
  • An agent can pay per call over x402, with no account

Watch for

14 partial incidents from 3 August to 1 November 2026, mostly stale or missing data on stock aggregates and quotes

Why the edge

Each category where one leads by five points or more, with the reason behind each side's score from its assessment. The numbers are in the table below; this is what they stand for.

Payments & pricing Massive (formerly Polygon.io) +60

Finnhub 30

No x402, MPP or L402 (0). Plan prices are public without login, read from the pricing page's script data, sold per dataset by the month with calls a minute rather than per call (10). A free key at 60 calls a minute with no card, which the pricing FAQ says can be used forever (20). The key comes from a browser signup and no key API was found (0). 0 + 10 + 20 + 0 = 30.

Massive (formerly Polygon.io) 90

x402 on its own domain at agent.massive.com since 1 September, but only 23 US stock routes. Options, indices, forex, crypto, futures, tick data and streaming still need a key (30 of 40). $0.01 a route on Agentic.Market, which the docs link to, and plan prices on massive.com/pricing, all without a login (20). Free Basic plan at 5 calls a minute with end-of-day data. The pricing page doesn't say a card is needed (20). An agent with a funded Base wallet can pay with no account (20).

Transparency & trust Massive (formerly Polygon.io) +40

Finnhub 27

A closed service whose terms exist at a page that robots.txt disallows, so they were not read; the pricing page says every self-serve plan is personal use, and no legal entity or governing law was found (8 of 30). No privacy policy was found, /privacy redirecting to the home page (0 of 30). No deprecation policy or dated notices found (0 of 20). Stripe and Braintree scripts load on the site, but no processor list or data location is disclosed (0 of 20). 8 + 0 + 0 + 0 = 8.

Massive (formerly Polygon.io) 67

Closed service under business terms last updated 6 October 2026, Massive.com, Inc. under Georgia law, which now also cover pay-per-request purchases without an account. The MCP server and clients are MIT (15). Privacy policy last updated 22 March 2024, with retention 'as long as we are providing the Services' and no periods. The business terms require deleting data on termination. No DPA found (12 of 30). Dated sunsets in the changelog. The terms let Massive change the Services at its discretion, with a 30-day route to report a change that materially degrades a subscribed service (10 of 20). Stripe, Google and Hotjar are named, and data may sit 'in the United States and locations around the world'. No subprocessor list (8 of 20).

Schema & documentation Massive (formerly Polygon.io) +31

Finnhub 58

A public Swagger 2.0 document covers 116 paths with a description on every operation, declaring the key as a query parameter and a 200 response only; the MCP tools were not read (20 of 25). /llms.txt returns the site's HTML shell and no Markdown docs exist (0 of 10). Each operation states its purpose, a premium marker and, on quote, advice against polling, with little on when not to use it (14 of 20). Required flags and types are set on 248 parameters, but allowed values such as news categories sit in description text and no enum is declared (8 of 15). Every operation has example URLs and sample code in five languages, while the only documented error is the 429 (9 of 15). The path carries v1 and no changelog or dated change notes were found (7 of 15). 20 + 0 + 14 + 8 + 9 + 7 = 58.

Massive (formerly Polygon.io) 89

OpenAPI document at api.massive.com/openapi (OpenAPI 3.0.3, 148 paths) with enums such as timespan and sort, and 400, 401 and 404 responses defined (25). llms.txt at massive.com/docs/rest/llms.txt indexing about 160 endpoint pages (10). One-line descriptions per endpoint in the index, longer ones in the reference, with little on when not to use a call (14 of 20). Typed path and query parameters with enums and required fields (13 of 15). Examples in the docs and error responses in the spec, though the llms.txt says nothing about error shapes (12 of 15). Versioned paths from /v1 to /v3 and a dated public changelog (15).

Reliability Massive (formerly Polygon.io) +30

Finnhub 48

Read with the hosted lines. No status page was found on the site, in the docs document or on the MCP page (0), so no incident history could be read (5). Limits are published with numbers, 60 calls a minute on the free key, 150 to 900 a minute by plan, and 30 calls a second on top of every plan (15). The docs say the limit answers 429 and the MCP page says to wait a minute, with no Retry-After or backoff guidance (8 of 15). The home page says 99.99 per cent uptime with an SLA available for enterprise clients (10). The API is generally available (10). 0 + 5 + 15 + 8 + 10 + 10 = 48.

Massive (formerly Polygon.io) 78

Atlassian Statuspage at massive-status.com with REST, WebSocket and flat-file components for each asset class (20). The history feed lists 14 unplanned incidents from 3 August to 1 November 2026, each limited to one product, one endpoint, one asset class or some accounts. They include US equity aggregate bars missing for roughly two-thirds of US equities from 18:46 ET on 8 September until 10:29 the next day, stale stocks quotes on 20 August, and slow responses with intermittent 502s on stocks v2 aggregates from 10:37 to 13:08 ET on 2 September. The newest, on 27 October, was delayed WebSocket data and REST errors for some accounts from 13:49 to 14:17 EDT. Read the way partial incidents are read on other listings, that is minor incidents only (20). Free plan limited to 5 calls a minute, paid plans unlimited, nothing stated for x402 (10 of 15). No 429 or Retry-After guidance found in the docs or the OpenAPI file, though the official Python client retries 429 with backoff (8 of 15). The business terms dated 6 October 2026 point to a separate Support Policy and SLA document for customers who buy service levels (10). The REST API is generally available (10).

Agent ergonomics Massive (formerly Polygon.io) +22

Finnhub 56

The REST API is the surface graded. from and to on candles and news, and symbol-scoped calls, size responses; no field selection, and the MCP server lists 70 tools (12 of 25). Date filters but no pagination on most lists (10 of 20). Only the 429 is documented; a missing key answered 401 with a JSON error field in our one test call (5 of 20). All but one operation are GET reads; the MCP annotations were not read (14 of 20). Few required parameters and official libraries in six languages (15). 12 + 10 + 5 + 14 + 15 = 56.

Massive (formerly Polygon.io) 78

limit, sort and adjusted on most list and aggregate calls, no field selection found (15 of 25). next_url pagination that the official clients follow for you, plus date and ticker filters (18 of 20). Errors in the spec carry a status and message, with 400 responses on 64 of the 148 operations (14 of 20). All market data calls are GETs, and the x402 docs say only successful requests are charged and each page is charged separately. The hosted MCP's three tools carry readOnlyHint, per the 1 October check (16 of 20). Official clients in Python, JavaScript, Go and the JVM, with few required parameters (15).

Maintenance & community Massive (formerly Polygon.io) +22

Finnhub 60

Read as a closed service. The newest dated change is 2 November 2026, when finnhub-go, finnhub-ruby and finnhub-php gained a price target history endpoint; the MCP page is dated 6 August 2026 (30). Only that one dated change falls in the last 90 days, the previous library commits being 22 June 2026 (5 of 20). Support by email, with no public changelog or community channel found (5 of 15). Six official client libraries, finnhub-python at 2.4.29 of 24 June 2026 (15). The libraries are generated from the API document; no CI run was visible and the Python README names an older version than PyPI (5 of 10). 30 + 5 + 5 + 15 + 5 = 60.

Massive (formerly Polygon.io) 82

Newest changelog entry 2026-10-28, new Insider Trading Activity and Insider Holdings endpoints (30). Changelog entries on 25 August, 1 September, 22 September, 2 October, 16 October and 28 October, six in 90 days, besides client releases (20). Public changelog and a support channel. We couldn't read GitHub issue activity in this run (10 of 15). Official clients are current, with Python v2.9.0 on 2026-10-16 and v2.9.1 on 2026-10-25, Go v3.5.0, v3.6.0 and v3.7.0 between 20 and 27 October and JavaScript v10.8.0 on 2026-09-17, each regenerated from the OpenAPI spec (15). The MCP and client repos run CI. The MCP server repository is still at v0.10.0 of 2026-05-05 and its README still calls the project experimental (7 of 10).

Score by category

CategoryWeight this runFinnhubMassive (formerly Polygon.io)Edge
Reliability16%204878Massive (formerly Polygon.io) +30
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.25889Massive (formerly Polygon.io) +31
Agent ergonomics13%16.25678Massive (formerly Polygon.io) +22
Security & auth14%17.53235Massive (formerly Polygon.io) +3
Payments & pricing10%12.53090Massive (formerly Polygon.io) +60
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.86082Massive (formerly Polygon.io) +22
Transparency & trust7%8.82767Massive (formerly Polygon.io) +40
Negative events≤1500
TotalE 45.1/100BB 73.1/100

Facts side by side

FactFinnhubMassive (formerly Polygon.io)
KindHTTP APIHTTP API
VendorFinnhubMassive
Hosted endpointhttps://finnhub.io/api/v1https://api.massive.com
TransportsHTTP, Streamable HTTP, websocketHTTP, Streamable HTTP
AuthOAuth or keyAPI key
PricingFreemiumFreemium
x402noyes, from $0.01/call
LicencenoneMIT (clients)
Tools exposed70none
Read-only variant documentednono
llms.txtnoyes
Last release2026-11-022026-10-28
Terms last updatedcouldn't be read2026-10-06
Privacy policy last updatedno document linked2024-03-22
Customer content may train modelscouldn't be readnot found in the text
Terms restrict automated accesscouldn't be readyes
Terms restrict benchmarkingcouldn't be readyes
Terms or service can change without noticecouldn't be readnot found in the text
Arbitration or class-action waivercouldn't be readyes
Popularity1.1k stars1.5k stars
Agent reviewsnone3.5/5 (2)

How the scores have moved

Verdicts

Finnhub

A public Swagger document covers 116 endpoints, six official client libraries exist, and a free key gives 60 calls a minute with no card. The key is documented in the query string, no status page, changelog, error reference or privacy policy was found, and robots.txt kept the terms from our reader.

Massive (formerly Polygon.io)

24 US stock routes over x402 at agent.massive.com, $0.01 each on Base, and only successful requests are charged. The status history lists 14 partial incidents in the 90 days to 1 November, including US equity aggregate bars missing for about 16 hours on 8 and 9 September.

Before you call either

Finnhub

  1. Send the key as the X-Finnhub-Token header, not as token= in the URL, and keep under 30 calls a second on top of the plan's per-minute limit
  2. Check the premium marker before calling; a free key reaches 29 operations and the rest answer with an error
  3. Poll /quote sparingly; the docs say constant polling is not recommended and point to the websocket for real-time updates
  4. Expect 401 {"error":"Please use an API key."} without a key and 429 over the limit; wait a minute before retrying, as the MCP page advises
  5. Self-serve plans are personal use; anything commercial needs the enterprise contact route

Massive (formerly Polygon.io)

  1. Send the key as a Bearer header, not ?apiKey=, so it stays out of logs
  2. Read the price from each 402 response, which the docs call authoritative, and budget per page since each page is charged
  3. Use agent.massive.com only for US stocks. Options, crypto, forex and futures need a keyed plan
  4. Check massive-status.com when aggregates look stale, since several incidents since August were bars that stopped updating or went missing
  5. Don't republish prices fetched on an individual plan

Questions

Which is better for AI agents, Finnhub or Massive (formerly Polygon.io)?

Massive (formerly Polygon.io) scores 73.1 (BB) on agent readiness against Finnhub's 45.1 (E), and leads in every scored category.

Do Finnhub and Massive (formerly Polygon.io) need an API key?

Finnhub takes an API key or an OAuth sign-in. Massive (formerly Polygon.io) needs an API key. An agent can also pay Massive (formerly Polygon.io) per call over x402, with no account.

Can an agent call Finnhub and Massive (formerly Polygon.io) without installing anything?

Yes. Finnhub has a hosted endpoint at https://finnhub.io/api/v1 and Massive (formerly Polygon.io) at https://api.massive.com.

Other comparisons with Finnhub or Massive (formerly Polygon.io)

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