Search and read ClinicalTrials.gov studies, sites and outcomes. Hosted by usefulapi — connect from Claude, Cursor, or any MCP client.
Team and Enterprise: an Owner adds the connector for the organization first.
Run this command, then run /mcp in Claude Code to log in:
Add to Cursor or add this to ~/.cursor/mcp.json:
{
"mcpServers": {
"clinicaltrialsgov": {
"url": "https://clinicaltrialsgov.usefulapi.io/mcp"
}
}
}Add to VS Code or add this to .vscode/mcp.json:
{
"servers": {
"clinicaltrialsgov": {
"type": "http",
"url": "https://clinicaltrialsgov.usefulapi.io/mcp"
}
}
}Other MCP clients (Windsurf, Cline, Zed and more): add the URL as a remote MCP server (Streamable HTTP). The client then opens the login page in your browser. Do not add an Authorization header: see Before you connect.
You do not need an account or a key for ClinicalTrials.gov. You log in with your email address and a 6-digit code.
ClinicalTrials.gov needs no credential.
Add only the URL. Do not add an Authorization header or an API key to the client config. The server signs you in with OAuth: the login page asks for your email address and a 6-digit code. If the config has such a header, remove it: some clients then send that header instead of the login token, and every call fails with 401.
Turn on the ClinicalTrials.gov connector, then ask in plain words. The AI picks the tools.
| Tool | Type | What it does |
|---|---|---|
search_studies | read | Search clinical trials (ClinicalTrials.gov) Search the ClinicalTrials.gov v2 study registry. Provide any combination of query terms (condition, intervention, title, location, sponsor, general term) — multiple query.* terms are ANDed together — plus optional filters (status, geo, advanced Essie expression, explicit NCT ids). Returns { totalCount?, studies: [...], nextPageToken? }. Use `fields` to trim the response to specific fields/modules, `sort` to order (e.g. '@relevance', 'LastUpdatePostDate:desc', 'EnrollmentCount:desc'), and pageSize/pageToken to page. GET /studies. |
get_study | read | Get a clinical trial by NCT ID Fetch a single ClinicalTrials.gov study by its NCT id (format NCT######## — the letters 'NCT' followed by digits, e.g. NCT00841061). Returns the full study object { protocolSection, derivedSection?, hasResults? }. Use `fields` to return only specific fields/modules. GET /studies/{nctId}. |
count_studies | read | Count matching clinical trials Return only the total NUMBER of studies matching a query, without fetching any records. Accepts the same query terms and filters as search_studies (term, condition, intervention, title, location, sponsor, status, geoFilter, advanced). Returns { totalCount }. GET /studies with countTotal=true and pageSize=1. |
list_field_values | read | List value statistics for study fields Discover valid values / enums for one or more study fields. Returns per-field value statistics — for each field: its type, unique-value count and topValues [{value, studiesCount}]. Great for finding valid enum values (e.g. OverallStatus, Phase) before building a filter. GET /stats/field/values. |
get_study_metadata | read | Get the study data-model (field tree) Return the ClinicalTrials.gov study data model as a tree of module nodes (each with name/title/type/children). Use this to explore what fields/modules exist and their nesting, to build `fields` selections or `sort`/filter expressions. GET /studies/metadata. |
get_studies_stats | read | Get study size statistics Return overall study-size statistics across the registry: { totalStudies, averageSizeBytes, percentiles, ranges, largestStudies }. Useful for understanding data volume. GET /stats/size. |
get_api_version | read | Get the ClinicalTrials.gov API version Return the ClinicalTrials.gov API version and the timestamp of the underlying data snapshot: { apiVersion, dataTimestamp }. GET /version. |
clinicaltrialsgov_usage_status | Usage status (free-tier meter) Report the caller's current free-tier usage this month: calls used, monthly limit, remaining, and whether the cap is reached. Read-only; does not count against the meter. | |
clinicaltrialsgov_request_feature | Request a missing feature Tell usefulapi that the user needs something the ClinicalTrials.gov tools cannot do yet (a missing tool, field or filter). Call it only when the user asks for something none of the tools can do, and tell the user that you send the request. Do not call it for errors or for normal requests. Do not include personal data, credentials or customer records. Stored with the product name and the client type (for example Claude or Cursor), without the user's account. At most 5 requests per day. Does not count against the meter. | |
clinicaltrialsgov_upgrade | Upgrade to Pro (unlimited) Subscribe to the Pro plan for UNLIMITED ClinicalTrials.gov tool calls (the free tier caps monthly usage). Choose monthly ($9/month) or yearly ($90/year — 2 months free) billing. Returns a Stripe Checkout link to open in your browser; after payment your account upgrades automatically. Does not count against the meter. | |
clinicaltrialsgov_cancel_subscription | Cancel the Pro subscription Cancel the caller's ClinicalTrials.gov Pro subscription at the end of the paid period (no refund for the current period; unlimited calls continue until then, then the free tier applies). Requires confirm: true. Run clinicaltrialsgov_upgrade later to undo the cancel before the period ends. Does not count against the meter. |
| Plan | Price | Limit |
|---|---|---|
| Free | $0 | 100 tool calls / month |
| Pro | $9/mo · $90/yr | Unlimited |
Pro covers this ClinicalTrials.gov server only. Subscribe with clinicaltrialsgov_upgrade (it returns a Stripe Checkout link). Cancel any time with clinicaltrialsgov_cancel_subscription: Pro continues to the end of the paid period, with no refund for the current period, and running clinicaltrialsgov_upgrade before then undoes the cancel. Or write to [email protected].
No. usefulapi is an independent service. It is not affiliated with or endorsed by ClinicalTrials.gov. The server calls the public ClinicalTrials.gov API for you.
Only an email address. You do not need a key for ClinicalTrials.gov.
No. Add only the URL. Do not add an Authorization header or an API key to the client config. The server signs you in with OAuth: the login page asks for your email address and a 6-digit code. If the config has such a header, remove it: some clients then send that header instead of the login token, and every call fails with 401.
All 7 ClinicalTrials.gov tools are marked read-only.
The Free plan gives 100 tool calls / month. Pro costs $9/mo or $90/yr, with unlimited tool calls, for this ClinicalTrials.gov server only. Run clinicaltrialsgov_usage_status to see how many calls you used.
Ask the AI to run clinicaltrialsgov_upgrade: it returns a Stripe Checkout link. To cancel, run clinicaltrialsgov_cancel_subscription. Pro continues to the end of the paid period.
Tell the AI what you wanted to do. It can send the request with clinicaltrialsgov_request_feature. We store the text with the server name, the type of AI client and the tool you tried, not with your account, and read every request when we plan new tools. You can send up to 5 requests per day.
Any client that supports remote MCP servers (Streamable HTTP) with OAuth login: Claude (web and desktop), Claude Code, Cursor, VS Code, Windsurf and others.
This is a Model Context Protocol endpoint — meant to be connected from an AI client, not opened in a browser. An invalid_token response at the URL is the auth gate working as designed; clients authenticate automatically.