Stock Quote API for AI Agents: 6 Best Compared (2026)面向 AI Agent 的股票报价 API：6 大方案对比（2026）
A technical comparison of 6 stock quote API providers — Polygon.io, Alpaca, Finnhub, Twelve Data, Alpha Vantage, and Marketstack — benchmarked on quote fields, latency, free tier limits, and AI agent integration patterns.
What is a Stock Quote API for AI Agents?
A stock quote API returns structured price data for publicly traded securities — including last price, bid/ask spread, volume, day high/low, and intraday range. For AI agents, the critical differentiators are which quote fields are available, whether data is real-time or delayed, and whether extended-hours data (pre-market and after-hours) is included.
Unlike a real-time stock price API that focuses on streaming price updates, a stock quote API provides a complete snapshot of the current market state for a given symbol — the full picture of supply (ask), demand (bid), and recent activity (last price, volume, VWAP). This snapshot data is what AI agents need for execution quality assessment, spread analysis, and pre/post-market monitoring.
The challenge for AI agent developers: not all quote APIs return the same fields. Some provide bid/ask spread but not VWAP. Others include pre-market prices but not after-hours. An AI agent that assumes a field is always present will silently degrade when a provider omits it. This guide benchmarks 6 providers on exactly which fields they return — so you know before you integrate.
The 8 Quote Fields That Matter for AI Agents
These eight fields define what a stock quote API can tell your agent. Missing fields are not just gaps — they are capabilities your agent loses.
| Field | What It Is | Why AI Agents Need It |
|---|---|---|
| Last Price | Most recent trade price | Core price signal — the baseline for every agent workflow |
| Bid Price | Highest buy offer on the order book | Best available exit price; essential for execution quality assessment |
| Ask Price | Lowest sell offer on the order book | Best available entry price; combined with bid = spread signal |
| VWAP | Volume-weighted average price (intraday) | Institutional benchmark — tells your agent if a trade was above or below the market average |
| Volume | Total shares traded today | Momentum and liquidity confirmation — price moves without volume may be noise |
| Day High/Low | Intraday price range | Range-based condition triggers — breakout detection, support/resistance proximity |
| Pre-Market Price | Price before regular market open | Early signal for overnight news, earnings reactions, and gap-up/gap-down detection |
| After-Hours Price | Price after regular market close | Earnings announcements typically come after close — agents need this to monitor post-release reactions |
6 Stock Quote APIs Compared
Quote field availability is the primary differentiator. Latency, free tier generosity, and AI agent SDK support follow.
| PROVIDER提供商 | Bid/Ask | VWAP | Extended Hours | Pre/Post Market | Free Tier | Latency | Starting Price |
|---|---|---|---|---|---|---|---|
| Polygon.io | ✓ | ✓ | ✓ | ✓ | Delayed only | <10ms | $29/mo |
| Alpaca | ✓ | ✓ | ✓ | ✓ | Real-time free | <100ms | Free |
| Finnhub | ✓ | ✗ | ✗ | ✗ | 300 calls/day | Sub-second | Free |
| Twelve Data | ✓ | ✓ | ✗ | ✗ | 800 req/day | Sub-second | Free |
| Alpha Vantage | ✓ | ✗ | ✗ | ✗ | 25 req/day | 1-5s | Free |
| Marketstack | ✗ | ✗ | ✗ | ✗ | 100 req/day EOD | 15min delayed | $9.99/mo |
Provider Deep Dives
1. Polygon.io — Most Complete Quote Fields
- Strengths: All 8 quote fields available, WebSocket real-time streaming, broad multi-asset coverage (stocks, options, forex, crypto), <10ms latency on paid plans
- Limitations: Free tier is delayed data only — real-time requires $29/mo minimum; no genuine free tier for development
- AI Agent Fit: Production agents that need complete quote snapshots with sub-10ms latency
2. Alpaca — Best Free Tier for Complete Quotes
- Strengths: All 8 quote fields available on the free tier, real-time data with no daily call cap, WebSocket streaming included, Python and JS SDKs
- Limitations: Primarily US equity coverage — international and multi-asset coverage is limited compared to Polygon.io or Twelve Data
- AI Agent Fit: The go-to choice for US stock monitoring agents on a budget
3. Finnhub — Simple Quote, Real-Time Free
- Strengths: Real-time bid/ask and last price on the free tier, WebSocket support included, 300 calls/day with 60 calls/min rate limit
- Limitations: No VWAP — a significant gap for execution-quality agents; no extended hours or pre/post-market data
- AI Agent Fit: Good for basic price monitoring; insufficient for agents that need execution benchmarks
4. Twelve Data — Best Balance of Fields and Free Tier
- Strengths: Bid/ask and VWAP included on the free tier, 800 requests/day — the highest daily REST limit among free quote APIs, 50+ exchanges covered
- Limitations: Free tier data is delayed; no extended hours pricing on any tier below paid plans; WebSocket requires paid
- AI Agent Fit: Best option for agents needing VWAP with a meaningful free daily allowance
5. Alpha Vantage — Accessible but Severely Limited
- Strengths: Simple REST API with clear documentation, bid/ask included, covers stocks, forex, and crypto in one API key
- Limitations: Only 25 requests/day — the most restrictive free tier; no VWAP; 15-minute delayed data; no WebSocket support
- AI Agent Fit: Useful for initial prototyping only. Any automated agent workflow will exhaust the daily quota in minutes
6. Marketstack — EOD Only, Not for Real-Time Agents
- Strengths: Broad global coverage with 80,000+ tickers, 100 requests/day on free tier for EOD data, affordable paid tier at $9.99/month
- Limitations: No bid/ask on any tier; EOD data only on free tier (15-minute delayed); no VWAP, extended hours, or real-time streaming
- AI Agent Fit: Suitable for historical analysis agents. Not suitable for any real-time monitoring workflow
Free Tier Comparison for AI Agent Development
| PROVIDER提供商 | Free Tier Type | Daily Limit | Real-Time? | Credit Card? | Commercial Use? | Best For |
|---|---|---|---|---|---|---|
| Alpaca | Genuinely Free | No hard cap (fair use) | Yes | No | Dev use free | Production US equity agents |
| Finnhub | Limited Free | 300 calls/day | Yes (limited) | No | Restricted | Development + low-volume prod |
| Twelve Data | Limited Free | 800 req/day | Delayed (free) | No | Non-commercial | Multi-asset research agents |
| Alpha Vantage | Limited Free | 25 req/day | Delayed 15min | No | Non-commercial | Prototyping only |
| Polygon.io | Delayed Only | None (paid) | Paid only | Required | Yes (paid) | Production (paid plans) |
| Marketstack | EOD Only | 100 req/day (EOD) | 15min delayed | Required | Yes (paid) | Historical/EOD analysis |
Key takeaway: Alpaca is the only provider offering genuinely free real-time quotes with all 8 fields — no daily cap, no credit card, and commercial dev use permitted. For agents that need VWAP on a free tier, Twelve Data provides the best balance (800 req/day, VWAP included, but delayed). For production agents requiring institutional latency and every quote field, Polygon.io is the standard — but it starts at $29/month with no free real-time tier.
Pre-Market and After-Hours Quotes for AI Agents
Extended hours data is not a luxury — it is operational necessity for several AI agent patterns. Earnings announcements are released after market close. Overnight news breaks before the open. An agent that only monitors regular-hours quotes is blind to the most important price moves of the day.
Pre-Market Quotes (4:00 AM – 9:30 AM ET)
Capture overnight reactions to earnings, geopolitical events, and sector news. Gap-up and gap-down detection requires pre-market prices — without them, your agent sees the move only after the open, when the opportunity has passed. Available from: Polygon.io, Alpaca.
After-Hours Quotes (4:00 PM – 8:00 PM ET)
Monitor post-earnings price reactions, guidance updates, and late-breaking corporate news. Most earnings releases hit at 4:00–4:30 PM ET. An agent without after-hours data won't see the market's verdict until the next morning. Available from: Polygon.io, Alpaca.
Only Polygon.io and Alpaca provide pre-market and after-hours quotes — and Alpaca includes them on the free tier. Finnhub, Twelve Data, and Alpha Vantage do not support extended hours data on any standard tier. If your agent monitors earnings reactions, overnight news impact, or pre-market gap signals, provider choice is effectively reduced to two options.
Unified Stock Quote Access via Capability Routing
Different providers name the same quote fields differently. Polygon.io returns VWAP as vw. Twelve Data returns it as vwap. Alpha Vantage does not return VWAP at all. An AI agent that hardcodes field names per provider accumulates parsing debt with every new integration — and silently drops data when a provider omits a field the agent expects.
QVeris solves this with a Discover → Inspect → Call protocol. Your agent describes what quote data it needs. QVeris discovers which providers support those fields, lets the agent inspect schemas and field availability before calling, and returns normalized field names regardless of which provider answers. The same vwap field is always called vwap — no matter who provided the data.
The routing layer handles provider discovery, field-name normalization, and response formatting. Your agent code stays consistent — it requests vwap and receives vwap, regardless of whether Polygon.io, Twelve Data, or Alpaca ultimately answered the call. Inspect Alpaca in QVeris →, inspect Alpha Vantage →, or read the REST API reference →.
Getting Started Checklist
QVeris provides a capability routing layer. Quote data comes from third-party providers. Field availability and limits are subject to change — verify official docs.
Get Complete Quote Data for Your AI Agent
QVeris normalizes quote fields across providers so your agent gets consistent bid/ask, VWAP, and extended hours data — without per-provider parsing logic. Discover and Inspect are free forever.
Compare Stock Quote Providers →对比股票报价提供商 →Read the REST API Reference阅读 REST API 参考Real-Time Stock Price API for AI Agents →
Compare 6 real-time stock price APIs with WebSocket streaming and AI agent integration.
Stock API Free Comparison →
Every free stock API compared with real tier limits and upgrade paths.
Free Financial API Comparison →
Compare 12 free financial APIs across stock, crypto, forex, news, and macro categories.
Market Data API for AI Agents →
Complete comparison of 7 market data providers across equities, crypto, forex, and options.
Stock Quote API FAQ
What is a stock quote API?
Which stock quote API has the best free tier?
Do free stock quote APIs include bid/ask spread?
Which stock quote API supports pre-market prices?
What is VWAP and which APIs provide it for free?
How do AI agents handle different quote field names across providers?
vw, Twelve Data calls it vwap, and Alpha Vantage does not provide it at all. Without normalization, your agent code must maintain per-provider field maps. A unified routing layer like QVeris normalizes field names across providers — your agent requests vwap and receives vwap, regardless of which provider answered. See the Unified Quote Access section for a code example.References & Sources
- Polygon.io Documentation — polygon.io/docs
- Alpaca Markets Documentation — docs.alpaca.markets
- Finnhub Documentation — finnhub.io/docs/api
- Twelve Data Documentation — twelvedata.com/docs
- Alpha Vantage Documentation — alphavantage.co/documentation
- Marketstack Documentation — marketstack.com/documentation
面向 AI Agent 的股票报价 API：6 大选择对比（2026）
6 大股票报价 API 提供商的技术对比 — Polygon.io、Alpaca、Finnhub、Twelve Data、Alpha Vantage 和 Marketstack — 基于报价字段、延迟、免费套餐限制和 AI Agent 集成模式进行基准测试。
什么是面向 AI Agent 的股票报价 API？
股票报价 API 返回公开交易证券的结构化价格数据 — 包括最新价格、买卖价差、成交量、日内最高/最低价和日内区间。对于 AI Agent，关键区分因素是哪些报价字段可用、数据是实时还是延迟的、以及是否包含盘前盘后数据。
与专注于流式价格更新的实时股价 API 不同，股票报价 API 提供特定标的当前市场状态的完整快照 — 供应（卖盘）、需求（买盘）和近期活动（最新价格、成交量、VWAP）的全貌。这种快照数据是 AI Agent 执行质量评估、价差分析和盘前盘后监控所需的信息。
AI Agent 开发者面临的挑战：并非所有报价 API 都返回相同的字段。有些提供买卖价差但不提供 VWAP。有些包含盘前价格但不包含盘后价格。假设某个字段始终存在的 AI Agent 会在提供商省略该字段时悄然退化。本指南对 6 个提供商返回的具体字段进行基准测试 — 让您在集成前就心中有数。
AI Agent 最关心的 8 个报价字段
这八个字段定义了股票报价 API 能告诉您的 Agent 什么信息。缺失的字段不仅仅是空白，而是您的 Agent 失去的能力。
| 字段 | 含义 | AI Agent 为什么需要它 |
|---|---|---|
| 最新价格 | 最近一笔成交价 | 核心价格信号，是各种 Agent 工作流的基准 |
| 买方报价 | 订单簿中的最高买入报价 | 当前可获得的最佳卖出价，是评估执行质量的关键 |
| 卖方报价 | 订单簿中的最低卖出报价 | 当前可获得的最佳买入价；与买方报价结合可计算价差 |
| VWAP | 成交量加权平均价（日内） | 机构常用基准，可帮助 Agent 判断成交价高于还是低于市场平均水平 |
| 成交量 | 当日累计成交股数 | 用于确认动量与流动性；没有成交量配合的价格波动可能只是噪声 |
| 日内最高 / 最低价 | 日内价格区间 | 用于区间条件触发，例如突破识别及支撑位、阻力位距离判断 |
| 盘前价格 | 常规交易时段开盘前的价格 | 用于捕捉隔夜新闻、财报反应和高开低开等早期信号 |
| 盘后价格 | 常规交易时段收盘后的价格 | 财报通常在收盘后发布，Agent 需要该字段监控发布后的市场反应 |
6 大股票报价 API 对比
报价字段可用性是首要区分因素。延迟、免费套餐慷慨度和 AI Agent SDK 支持紧随其后。
| 提供商 | 买价/卖价 | VWAP | 延长交易时段 | 盘前/盘后 | 免费额度 | 延迟 | 起始价格 |
|---|---|---|---|---|---|---|---|
| Polygon.io | ✓ | ✓ | ✓ | ✓ | 仅延迟数据 | <10ms | $29/mo |
| Alpaca | ✓ | ✓ | ✓ | ✓ | 免费实时数据 | <100ms | 免费 |
| Finnhub | ✓ | ✗ | ✗ | ✗ | 300 次调用/天 | 亚秒级 | 免费 |
| Twelve Data | ✓ | ✓ | ✗ | ✗ | 800 次请求/天 | 亚秒级 | 免费 |
| Alpha Vantage | ✓ | ✗ | ✗ | ✗ | 25 次请求/天 | 1–5 秒 | 免费 |
| Marketstack | ✗ | ✗ | ✗ | ✗ | 100 次请求/天（日终） | 延迟 15 分钟 | 每月 9.99 美元 |
各提供商深度分析
1. Polygon.io：报价字段最完整
- 优势：提供全部 8 个报价字段，支持 WebSocket 实时流，广泛覆盖股票、期权、外汇和加密货币；付费套餐延迟低于 10 毫秒
- 限制：免费套餐仅提供延迟数据；实时数据最低需每月 29 美元，且没有真正适合开发的免费实时套餐
- AI Agent 适用性：适合需要完整报价快照和低于 10 毫秒延迟的生产级 Agent
2. Alpaca：完整报价的最佳免费额度
- 优势：免费套餐提供全部 8 个报价字段，实时数据没有每日调用上限，并包含 WebSocket 流以及 Python 和 JavaScript SDK
- 限制：主要覆盖美股；与 Polygon.io 或 Twelve Data 相比，国际市场和多资产覆盖有限
- AI Agent 适用性：预算有限的美股监控 Agent 的首选
3. Finnhub：简单报价，免费实时
- 优势：免费套餐提供实时买价、卖价和最新价，并包含 WebSocket；每日 300 次调用，每分钟最多 60 次
- 限制：不提供 VWAP，对执行质量 Agent 是明显缺口；也没有延长交易时段或盘前盘后数据
- AI Agent 适用性：适合基础价格监控，但不能满足需要执行基准的 Agent
4. Twelve Data：字段与免费额度平衡较好
- 优势：免费套餐包含买卖报价和 VWAP，每日可请求 800 次，是免费报价 API 中较高的 REST 日限额，并覆盖 50 多家交易所
- 限制：免费套餐数据有延迟；付费以下套餐不提供延长交易时段报价，WebSocket 也需要付费
- AI Agent 适用性：需要 VWAP 且希望获得可用免费日额度的 Agent 的较佳选择
5. Alpha Vantage：易用但限制较多
- 优势：REST API 简单、文档清晰，包含买卖报价，并可用一个 API 密钥访问股票、外汇和加密货币数据
- 限制：每天仅 25 次请求，是限制最严的免费套餐；不提供 VWAP，数据延迟 15 分钟，也不支持 WebSocket
- AI Agent 适用性：仅适合初步原型验证；任何自动化 Agent 工作流都可能在几分钟内耗尽每日额度
6. Marketstack：仅提供日终数据，不适合实时 Agent
- 优势：全球覆盖广，包含 80,000 多个股票代码；免费套餐的日终数据每天可请求 100 次，付费套餐起价为每月 9.99 美元
- 限制：所有套餐都没有买卖报价；免费套餐只有日终数据且延迟 15 分钟，不提供 VWAP、延长交易时段或实时流
- AI Agent 适用性：适合历史分析 Agent，不适合任何实时监控工作流
AI Agent 开发免费套餐对比
| 提供商 | 免费额度类型 | 每日限制 | 是否实时 | 是否需要信用卡 | 是否可商用 | 最适合 |
|---|---|---|---|---|---|---|
| Alpaca | 真正免费 | 无硬性上限（合理使用） | 是 | 否 | 开发用途免费 | 生产级美股 Agent |
| Finnhub | 免费额度有限 | 300 次调用/天 | 支持（有限） | 否 | 受限 | 开发与低调用量生产场景 |
| Twelve Data | 免费额度有限 | 800 次请求/天 | 免费套餐为延迟数据 | 否 | 仅限非商业用途 | 多资产研究 Agent |
| Alpha Vantage | 免费额度有限 | 25 次请求/天 | 延迟 15 分钟 | 否 | 仅限非商业用途 | 仅适合原型验证 |
| Polygon.io | 仅延迟数据 | 无（付费套餐） | 仅付费 | 需要 | 支持（付费） | 生产环境（付费套餐） |
| Marketstack | 仅日终数据 | 100 次请求/天（日终） | 延迟 15 分钟 | 需要 | 支持（付费） | 历史 / 日终分析 |
关键结论：Alpaca 是唯一提供真正免费实时报价且包含全部 8 个字段的提供商 — 无每日上限、无需信用卡、允许商业开发使用。对于需要在免费套餐中使用 VWAP 的 Agent，Twelve Data 提供了最佳平衡（800 次/天、包含 VWAP、但数据延迟）。对于需要机构级延迟和全部报价字段的生产 Agent，Polygon.io 是标准选择 — 但起价 $29/月且无免费实时套餐。
AI Agent 的盘前和盘后报价
盘前盘后数据不是奢侈品 — 对多种 AI Agent 模式而言是运营必需品。财报在收盘后发布。隔夜新闻在开盘前爆出。只监控常规时段报价的 Agent 对当天最重要的价格波动视而不见。
盘前报价（美东时间 4:00–9:30）
用于捕捉财报、地缘政治事件和行业新闻引发的隔夜反应。识别高开和低开需要盘前价格；缺少这些数据时，Agent 只能在开盘后看到波动，机会可能已经过去。提供商：Polygon.io、Alpaca。
盘后报价（美东时间 16:00–20:00）
用于监控财报发布后的价格反应、业绩指引更新和盘后突发公司新闻。大多数财报在美东时间 16:00–16:30 发布。缺少盘后数据的 Agent 要到次日早晨才能看到市场判断。提供商：Polygon.io、Alpaca。
只有 Polygon.io 和 Alpaca 提供盘前和盘后报价 — 而且 Alpaca 在免费套餐中包含了这些数据。Finnhub、Twelve Data 和 Alpha Vantage 在任何标准套餐中都不支持盘前盘后数据。如果您的 Agent 监控财报反应、隔夜新闻影响或盘前缺口信号，提供商选择实际上只有两个。
通过能力路由统一访问股票报价
不同提供商对相同的报价字段使用不同的名称。Polygon.io 将 VWAP 返回为 vw。Twelve Data 将其返回为 vwap。Alpha Vantage 根本不返回 VWAP。为每个提供商硬编码字段名称的 AI Agent 会随着每个新集成积累解析债务 — 并在提供商省略 Agent 期望的字段时悄然丢失数据。
QVeris 通过 发现 → 检查 → 调用 协议解决这一问题。您的 Agent 描述它需要什么报价数据。QVeris 发现哪些提供商支持这些字段、让 Agent 在调用前检查 Schema 和字段可用性、并返回标准化的字段名称 — 无论哪个提供商响应。vwap 字段始终叫做 vwap — 不管是谁提供的数据。
路由层处理提供商发现、字段名称标准化和响应格式化。您的 Agent 代码保持一致 — 它请求 vwap 就收到 vwap，无论最终响应的是 Polygon.io、Twelve Data 还是 Alpaca。在 QVeris 中查看 Alpaca →、查看 Alpha Vantage →，或阅读 REST API 参考 →。
快速上手指南
QVeris 提供能力路由层。报价数据来自第三方提供商。字段可用性和限制可能随时变更 — 请验证官方文档。
为您的 AI Agent 获取完整报价数据
QVeris 跨提供商标准化报价字段，让您的 Agent 获得一致的买卖价差、VWAP 和盘前盘后数据 — 无需针对每个提供商编写解析逻辑。Discover 和 Inspect 永久免费。
对比股票报价提供商 →阅读 REST API 参考面向 AI Agent 的实时股票价格 API →
对比 6 款支持 WebSocket 流式传输的实时股票价格 API，并说明 AI Agent 集成方式。
免费股票 API 对比 →
对比各款免费股票 API 的真实套餐限制与升级路径。
免费金融 API 对比 →
对比覆盖股票、加密货币、外汇、新闻与宏观数据的 12 款免费金融 API。
面向 AI Agent 的市场数据 API →
全面对比覆盖股票、加密货币、外汇与期权的 7 家市场数据供应商。
股票报价 API 常见问题
什么是股票报价 API？
哪个股票报价 API 免费额度最好？
免费股票报价 API 包含买卖价差吗？
哪个股票报价 API 支持盘前价格？
什么是 VWAP，哪些 API 免费提供？
AI Agent 如何处理不同供应商的报价字段差异？
vw，Twelve Data 称为 vwap，Alpha Vantage 根本不提供。没有标准化的情况下，您的 Agent 代码必须维护每个提供商的字段映射。像 QVeris 这样的统一路由层跨提供商标准化字段名称 — 您的 Agent 请求 vwap 就收到 vwap，无论哪个提供商响应。请参阅统一报价访问部分的代码示例。参考资料与来源
- Polygon.io 文档 — polygon.io/docs
- Alpaca Markets 文档 — docs.alpaca.markets
- Finnhub 文档 — finnhub.io/docs/api
- Twelve Data 文档 — twelvedata.com/docs
- Alpha Vantage 文档 — alphavantage.co/documentation
- Marketstack 文档 — marketstack.com/documentation