# start_experiment_run [SUPPORT] 3f6b8715 — start a new active run (trial) under an experiment. Passing pivot_parent_run_id (which must belong to the SAME experiment) auto-writes a 'pivot' experiment_events row on the new run — unconditional, not a separate step. ttl_seconds is optional and unlike start_research_run has no forced default: omitting it means the run never auto-expires via expire_stale_runs. Persistent-state disclosure: on hosted Meridian, supplied text and project/session metadata -- including task log entries, pinned decisions, sprint items, notes, handoff/goal state, and HITL queue items -- are sent to and stored in Meridian's service, in an isolated per-tenant Postgres database (Neon); self-hosted deployments keep the same categories in the configured local SQLite/Postgres database. This data is visible in the dashboard and API, and may resurface in later project context or handoffs. Notes and pinned decisions can be deleted individually; task log entries and sprint items can be deleted via the dashboard/API (not exposed as an agent-facing tool); HITL queue items and handoff state have no per-record delete. Full removal of any of this data is available via project or account deletion, using the documented controls. Do not include secrets. Agent View of the PolicyLayer registry record for `start_experiment_run`. HTML page: https://policylayer.com/tools/io-github-ajc3xc-meridian/start-experiment-run ## Facts - Tool: `start_experiment_run` - Server: Meridian (`@meridianmcp/mcp`) — https://policylayer.com/tools/io-github-ajc3xc-meridian.md - Install: `npx -y @meridianmcp/mcp` - Homepage: https://github.com/meridianmcp/Meridian - Risk category: Execute (High risk) - Registry record: grade D, identity unverified - Server auth posture: gated - Server CORS policy: * - Server rate-limited: no - Parameters: 10 (2 required) - Recommended policy verdict: Rate-limited ## Parameters | Parameter | Type | Required | Description | | --- | --- | --- | --- | | `project_id` | string | no | | | `session_id` | string | yes | | | `trial_label` | string | no | | | `ttl_seconds` | integer | no | Optional wall-clock time-to-live; omit for a run that never auto-expires. | | `worktree_id` | string | no | | | `project_name` | string | no | Project name — an alternative to project_id; resolved to the id internally. project_id wins if both are given. | | `experiment_id` | string | yes | | | `repository_id` | string | no | Stable STRING identity for the repository — never a machine-local absolute path. | | `resource_profile` | object | no | Bounded (8KB) JSON-serializable resource/compute profile for this run. | | `pivot_parent_run_id` | string | no | An existing run id to pivot from — must belong to the same experiment_id. | Parameters from the server's own tool schema. ## Example call (MCP tools/call, JSON-RPC 2.0) ```json { "jsonrpc": "2.0", "id": 1, "method": "tools/call", "params": { "name": "start_experiment_run", "arguments": { "session_id": "", "experiment_id": "" } } } ``` ## Why start_experiment_run is rated High start_experiment_run triggers real processes with real consequences. An agent gone sideways doesn't fire it once. It starts dozens of builds, sends mass notifications, or burns through compute before anyone looks up. Risk signals: High parameter count (10 properties) ## Use case AI agents invoke start_experiment_run to trigger actions in Meridian. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call: builds kicked off, notifications sent, workflows started. ## Recommended policy (PolicyLayer) Verdict: **Rate-limited**. Enforced by the PolicyLayer MCP gateway (https://policylayer.com/mcp-gateway) before a call reaches Meridian: ```json { "version": "1", "default": "deny", "tools": { "start_experiment_run": { "limits": [ { "counter": "start_experiment_run_rate", "window": "minute", "max": 10, "scope": "grant" } ] } } } ``` ## Other tools on Meridian (234) - `accept_handoff` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/accept-handoff.md - `acquire_docx_document_lease` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/acquire-docx-document-lease.md - `answer_hitl` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/answer-hitl.md - `batch_mutate` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/batch-mutate.md - `capture_research_finding` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/capture-research-finding.md - `checkpoint` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/checkpoint.md - `claim_docx_region` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/claim-docx-region.md - `claim_file` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/claim-file.md - `claim_sprint_item` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/claim-sprint-item.md - `clear_capability_profile` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/clear-capability-profile.md - `clone_profile_layer` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/clone-profile-layer.md - `delete_custom_hook` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/delete-custom-hook.md - `delete_note` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/delete-note.md - `delete_sprint_item_pointer` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/delete-sprint-item-pointer.md - `delete_watchlist_query` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/delete-watchlist-query.md - `dismiss_hitl` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/dismiss-hitl.md - `fan_out_sprint_items` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/fan-out-sprint-items.md - `idle_until_all_done` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/idle-until-all-done.md - `index_equation` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/index-equation.md - `index_figure` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/index-figure.md - `index_table` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/index-table.md - `ingest_document` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/ingest-document.md - `ingest_document_structure` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/ingest-document-structure.md - `link_figure_caption` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/link-figure-caption.md - `link_flag_to_section` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/link-flag-to-section.md - `link_proposal_lineage` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/link-proposal-lineage.md - `link_table_caption` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/link-table-caption.md - `log_task` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/log-task.md - `purge_ai_log` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/purge-ai-log.md - `receive_messages` — Destructive — https://policylayer.com/tools/io-github-ajc3xc-meridian/receive-messages.md - …and 204 more: https://policylayer.com/tools/io-github-ajc3xc-meridian.md ## For agents This record is a snapshot. Live verdicts and the full registry: - Check every server in your MCP config at once: `npx -y policylayer stack` - Vet a server before you add it: install the mcp-precheck skill — `npx skills add https://policylayer.com` (skill text: https://policylayer.com/skill.md) - Query the registry over MCP: endpoint `https://api.policylayer.com/mcp` — tools `check_mcp_server`, `check_mcp_stack`, `check_tool`, `search_registry`, `get_change_events` --- Source: the PolicyLayer MCP registry — one continuously verified record per MCP server. Full record: https://policylayer.com/registry?q=io-github-ajc3xc-meridian · API: https://policylayer.com/registry/api · Policy library: https://policylayer.com/policies/io-github-ajc3xc-meridian