Endpoint and authentication

Endpoint

URL: https://app.getcassis.com/mcp/
Transport: Streamable HTTP. No stdio mode.
Auth: OAuth 2.1 for interactive clients, or a long-lived API key as a bearer token for non-interactive agents and scripts. Any Cassis account works, including a sample-demo signup.
Keys: Prefix sk-k6-, issued by any member from API keys in the account menu, and valid for up to a year. A key acts as the person who created it. See Members and roles.

With OAuth, the client opens a browser, you sign in with your Cassis account, and the token is stored and refreshed automatically. An expired session just re-runs the flow.

Connecting a client

Any client that supports remote MCP servers over Streamable HTTP can connect. Add the endpoint above and use OAuth when the client supports it; the tabs below are examples for three common clients.

bash

claude mcp add --transport http cassis https://app.getcassis.com/mcp/

Or type /mcp inside Claude Code. For a project-scoped, secret-free config committed to the repository:

.mcp.json

{
"mcpServers": {
  "cassis": {
    "type": "http",
    "url": "https://app.getcassis.com/mcp/"
  }
}
}

Settings, then Connectors, then Add custom connector. Paste the endpoint URL and sign in when the browser opens.

Settings, then MCP, then Add new MCP server. Paste the endpoint URL, transport HTTP.

For a non-interactive agent, load an API key into the environment and send it instead of running OAuth:

bash

curl -H "Authorization: Bearer ${CASSIS_API_KEY}" https://app.getcassis.com/mcp/

The tool surface

Twelve tools in six groups. The server is read-heavy on purpose: it answers questions, reports project status, reads the source schema, reads the data-source review queue, and triages detected issues. Its only write is update_issue_status.

Group	Tools	What for
Query	ask_question	Ask about the data and get an answer, the SQL, and the results
Discovery	ping, list_projects	Confirm the server is reachable, and find the project to work with
Project state	get_project_status, get_source_schema	Read what is published, the git-sync state, and the schema beneath the ontology
Data source review	list_source_changes, get_source_change	Read the schema drift waiting for review; approving or dismissing stays in the app
Issue triage	list_issues, get_issue, get_issue_evidence, update_issue_status	Work the queue of problems detected from real conversations and failing evals
Evals	get_eval_run	Read an eval run’s status and per-case results

Every tool takes project_id except ping and list_projects. Start with list_projects to find it.

There is no ontology tool

The server does not read or edit the ontology. An agent reads it as files in a checkout, changes it there, and opens a pull request, which is why agent-driven curation requires the git path.

To do this	Use
Read the current ontology	A repository checkout. `cassis ontology pull` materializes one
Change the ontology	Edit the files in the repository, then open a pull request. See the git-managed curation workflow
Validate a change	cassis ontology check, cassis ontology fmt
Test that a change works	cassis ontology test
Check for regressions	cassis eval run
Publish	Merge to the default branch. Cassis imports and publishes a new version

Client behavior matters. Surface a plan and its assumptions when ask_question returns needs_execution, and execute it only after the user approves. Preserve chat_id for follow-ups. For ontology work, use a repository checkout and the CLI. Stop at the pull request unless the repository owner explicitly authorizes the agent to merge after required checks pass. Asking questions over MCP does not require a local CLI install.

Error convention

Every tool reports a failure as an error key in place of its normal fields, rather than raising. Expired or revoked credentials return HTTP 401: OAuth clients re-run the flow, and an API key has to be replaced. Full limits are in Limits and errors.