Constituents with weights
The latest complete composition of each index, with the fund and the date every list came from named on the response.
Seven US indexes · REST API · MCP
Stock index constituents API and MCP server
Read the composition of seven US stock indexes, the S&P 500, S&P MidCap 400 and S&P SmallCap 600, the Nasdaq-100, the Russell 1000 and Russell 2000 and the Dow Jones Industrial Average, as their full-replication tracking funds disclose it. Pull constituents, membership changes and rebalance forecasts over the REST API, or ask Claude, ChatGPT or any MCP client what is likely to join the S&P 500.
Using ChatGPT or Claude? Add this data to your AI — no code needed.
Free: 100 requests a day, no credit card. One account works with REST and MCP.
Works with
Claude
ChatGPT
Gemini
MCP
What the API and the MCP tools cover
Both surfaces read the same store the Equibles pages render, so a figure on the site and a figure in your code agree.
Membership changes
Additions and deletions between two observations, dated by the pair of observation dates the source supports rather than a single effective date.
Rebalance forecasts
Rules-based scorecards for the six indexes with published entry rules: screens for the S&P family, rankings for Russell and the Nasdaq-100, and a 90-day join and exit probability for the S&P 500.
REST endpoints and MCP tools
Every endpoint below is a GET under the api.equibles.com/v1 base URL, authenticated with an API key. Each MCP tool answers the same question in plain English from Claude, ChatGPT or any connected client.
GET /v1/indexesGET /v1/indexes/{index}GET /v1/indexes/{index}/changesGET /v1/indexes/{index}/forecast
GetIndexComposition
GetIndexChanges
GetIndexForecast
The same question, three ways
One free key covers the REST API and the MCP server; the browser needs no key at all.
REST
curl "https://api.equibles.com/v1/indexes/sp-500" -H "Authorization: Bearer eq_YOUR_KEY"
MCP, in Claude or ChatGPT
“Using Equibles, which companies are most likely to be added to the S&P 500 at the next rebalance?”
Name Equibles in the prompt so the model calls the tool instead of answering from memory. Connection guides
Read the provenance correctly
Every constituent list is a full-replication tracking fund's own disclosed holdings, taken from an SEC Form N-PORT filing or from the holdings file the fund publishes daily. No index-provider licence is involved and none is needed: a fund that replicates an index in full holds the index, and it files what it holds.
A list is published only once a fund's filing has arrived whole. A filing that arrived narrowed is stored but never published, because a partial list would read as an index that had shrunk.
Source: SEC Form N-PORT data sets.
What the API preserves
- The fund and the date behind every constituent list
- Shares and value as the fund's own position, never restated as the company's
- Rows the fund reported that could not be matched to a tracked company, kept under the fund's own name
- The observed and previous dates behind a membership change
- Index names resolved by slug or name, with an ambiguous spelling refused rather than guessed
Use the data in code, AI, or the browser
Choose the interface that fits the work; all three read the same store.
Frequently asked questions
What is a stock index constituents API?
It returns the membership of an index as structured data: each constituent with its weight, the changes between observations, and for six of the seven indexes a rules-based forecast of the next rebalance.
Where does the composition come from?
From a full-replication tracking fund's own disclosed holdings, either an SEC Form N-PORT filing or the holdings file the fund publishes daily. Every response names the fund and the date. No index-provider licence is involved.
How fresh is it?
Daily where a fund publishes its holdings file daily, quarterly where the only source is an N-PORT filing. A list is published only once a filing has arrived whole; a narrowed filing is stored and never published.
Can I get index constituents in Claude or ChatGPT?
Yes. Connect the Equibles MCP server and ask for an index by name or slug; GetIndexComposition returns the constituents, GetIndexChanges the additions and deletions and GetIndexForecast the rebalance outlook. The REST API returns the same lists as JSON.
Is there a free index constituents API?
Yes. The Equibles free tier includes 100 requests a day, shared across the REST API and MCP server, with no credit card. Paid plans raise the limit.
Start reading index membership.
One free key for constituents, membership changes and rebalance forecasts.