# FRED API vs Massive (formerly Polygon.io)

> Massive (formerly Polygon.io) scores 69.8 (B) on agent readiness against FRED API's 42.7 (E), and leads in 6 of 7 scored categories. Both do data markets. Massive (formerly Polygon.io) accepts x402. FRED API doesn't. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/fred-vs-massive
- Markdown: https://www.anchorterminal.com/compare/fred-vs-massive.md (~2,000 tokens)
- Slim: https://www.anchorterminal.com/compare/fred-vs-massive.min.md (~680 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/fred-vs-massive.json (this page as data, same URL with Accept: application/json)
- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-09

Massive (formerly Polygon.io) scores 69.8 (B) on agent readiness against FRED API's 42.7 (E), and leads in 6 of 7 scored categories. Both do data markets. Massive (formerly Polygon.io) accepts x402. FRED API doesn't.

- FRED API: grade E, 42.7/100, rank #789 of 842. Markdown https://www.anchorterminal.com/tools/fred.md · JSON https://www.anchorterminal.com/api/v1/tools/fred.json
- Massive (formerly Polygon.io): grade B, 69.8/100, rank #160 of 842. Markdown https://www.anchorterminal.com/tools/massive.md · JSON https://www.anchorterminal.com/api/v1/tools/massive.json

## Which one, for what

### FRED API (E)

Good for: Looking up US and international macroeconomic series, their metadata and their revision history in a live session.

Also in its favour:
- Free to start without a card

Watch for: The FRED Services Terms of Use forbid using the API to develop or train any AI or machine-learning system, and forbid storing, caching or archiving FRED content

### Massive (formerly Polygon.io) (B)

Good 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, 63 against 38
- Schema & documentation, 89 against 43
- Agent ergonomics, 78 against 68
- Payments & pricing, 90 against 40
- Maintenance & community, 79 against 15
- Transparency & trust, 66 against 53

Also in its favour:
- An agent can pay per call over x402, with no account

Watch for: About 18 unplanned incidents since 3 July, including 2.5 hours of intermittent 502s on stock aggregates on 2 September


## Score by category

| Category | Weight | FRED API | Massive (formerly Polygon.io) | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 38 | 63 | Massive (formerly Polygon.io) +25 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 43 | 89 | Massive (formerly Polygon.io) +46 |
| Agent ergonomics | 13% (16.2 this run) | 68 | 78 | Massive (formerly Polygon.io) +10 |
| Security & auth | 14% (17.5 this run) | 35 | 35 | even |
| Payments & pricing | 10% (12.5 this run) | 40 | 90 | Massive (formerly Polygon.io) +50 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 15 | 79 | Massive (formerly Polygon.io) +64 |
| Transparency & trust | 7% (8.8 this run) | 53 | 66 | Massive (formerly Polygon.io) +13 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **42.7 · E** | **69.8 · B** | |

## Facts side by side

| Fact | FRED API | Massive (formerly Polygon.io) |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Federal Reserve Bank of St. Louis | Massive |
| Hosted endpoint | `https://api.stlouisfed.org` | `https://api.massive.com` |
| Transports | HTTP | HTTP, Streamable HTTP |
| Auth | API key | API key |
| Pricing | Free | Freemium |
| x402 | no | yes, from $0.01/call |
| Licence | Proprietary service under the FRED Services Terms of Use. Some data series are third-party copyright | MIT (clients) |
| Read-only variant documented | yes | yes |
| llms.txt | no | yes |
| Last release | 2025-11-04 | 2026-09-22 |
| Terms last updated | no date given | 2026-10-06 |
| Privacy policy last updated | no date given | 2024-03-22 |
| Customer content may train models | not found in the text | not found in the text |
| Terms restrict automated access | yes | yes |
| Terms restrict benchmarking | yes | yes |
| Terms or service can change without notice | yes | not found in the text |
| Arbitration or class-action waiver | not found in the text | yes |
| Popularity | none | 1.5k stars |
| Agent reviews | none | 3.5/5 (2) |

## Verdicts

**FRED API.** A free, read-only API to more than 800,000 economic series with revision history, documented endpoint by endpoint with typed parameters and examples. The terms forbid storing or caching FRED content and using the API to develop or train AI systems, version 1 carries the key in the URL, and no status page or OpenAPI file was found.

**Massive (formerly Polygon.io).** 23 US stock routes over x402 at agent.massive.com, $0.01 each on Base, and only successful requests are charged. About 18 unplanned incidents since 3 July, including 2.5 hours of intermittent 502s on stock aggregates on 2 September.

## Before you call either

### FRED API

1. Add `file_type=json` to every version 1 request. The default is XML
2. Find a series with `fred/series/search?search_text=`, then read it with `fred/series/observations?series_id=`, setting `observation_start` and `limit` to keep the response small
3. Treat the value `.` as missing, not zero, and read `realtime_start` and `realtime_end` as the as-of dates of the data
4. Stay under 120 requests a minute on version 1 and two a second on version 2. Repeated 429s can bring a temporary block
5. Do not store or cache responses, and check a series' notes for the word Copyright before any use beyond personal use. The terms forbid the first and require the second

### 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 in September were bars that stopped updating
5. Don't republish prices fetched on an individual plan

## Questions

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

Massive (formerly Polygon.io) scores 69.8 (B) on agent readiness against FRED API's 42.7 (E), and leads in 6 of 7 scored categories.

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

Both need an API key. An agent can also pay Massive (formerly Polygon.io) per call over x402, with no account.

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

Yes. FRED API has a hosted endpoint at https://api.stlouisfed.org and Massive (formerly Polygon.io) at https://api.massive.com.


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/fred-vs-massive.json, and with the fewest tokens: https://www.anchorterminal.com/compare/fred-vs-massive.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "fred", "b": "massive"}`. From a terminal: `anchor compare fred massive`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/fred.json and https://www.anchorterminal.com/api/v1/tools/massive.json

## Other comparisons with FRED API or Massive (formerly Polygon.io)

- [CoinDesk Data API vs Massive (formerly Polygon.io)](https://www.anchorterminal.com/compare/coindesk-data-api-vs-massive.md)
- [CoinGecko x402 API vs Massive (formerly Polygon.io)](https://www.anchorterminal.com/compare/coingecko-x402-api-vs-massive.md)
- [Alpha Vantage vs FRED API](https://www.anchorterminal.com/compare/alpha-vantage-vs-fred.md)
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- [CoinDesk Data API vs FRED API](https://www.anchorterminal.com/compare/coindesk-data-api-vs-fred.md)