# New Sep > Scaffold a sep-NNNN.yaml requirement-traceability file for the MCP conformance repo from a SEP PR's spec diff. Runs the new-sep CLI, then parses the modelcontextprotocol/modelcontextprotocol spec diff to populate `requirements[]` with the RFC 2119 sentences and proposed check IDs. - Skill: `modelcontextprotocol/new-sep` (Agent Skill) - Install (CLI): `npx skillmds@latest add modelcontextprotocol/new-sep` - Raw SKILL.md: https://api.skillmd.com/api/skills/modelcontextprotocol/new-sep/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: AI & ML - Author: modelcontextprotocol (https://skillmd.com/u/modelcontextprotocol) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/modelcontextprotocol/new-sep --- # new-sep: SEP traceability YAML scaffolding You are bootstrapping a `sep-NNNN.yaml` file for a new SEP in the MCP conformance repo. The output is the requirement-traceability file specified by SEP-2484: a YAML that maps each normative sentence from the SEP's spec diff to a `check:` ID (testable) or an `excluded:` reason (not testable). The CLI gets the skeleton; you fill in the rows by reading the spec diff. ## Step 0: Pre-flight checks Before doing anything else, verify GitHub CLI authentication: ```bash gh auth status 2>&1 ``` If this fails, stop immediately and tell the user: > GitHub authentication is required for this skill. Please run `gh auth login` first, then re-run. Verify you're running inside the conformance repo: ```bash test -f package.json && jq -r '.name' package.json ``` The name should be `@modelcontextprotocol/conformance`. If not, stop and ask the user to `cd` into the conformance repo first. ## Step 1: Parse arguments Extract from the user's input: - **sep-number** (required): the SEP number, e.g. `2164`. This is also the PR number in `modelcontextprotocol/modelcontextprotocol` by convention. ## Step 2: Generate the skeleton Run the CLI: ```bash npm run --silent build node dist/index.js new-sep ``` (For development against a non-built source tree: `npx tsx src/index.ts new-sep ...`.) The CLI writes `src/seps/sep-.yaml` with `sep`, `spec_url`, and two TODO `requirements[]` rows. Capture the output path from the CLI's `Wrote …` line and remember it as `$YAML`. If the CLI errors with "does not change any docs/specification/draft/\*.mdx", the SEP's spec changes landed in a separate PR — ask the user for the spec file path and rerun with `--spec-path docs/specification/draft/`. Do not guess. ## Step 3: Fetch the spec diff `AGENTS.md` (lines 64–72) is explicit that severity must come from the spec text itself, not the SEP markdown or the conformance PR description: ```bash gh api "repos/modelcontextprotocol/modelcontextprotocol/pulls//files" \ --jq '.[] | select(.filename | test("^docs/specification/draft/.*\\.mdx$")) | {filename, patch}' ``` For each file, pull the added (`+`-prefixed) lines from `patch`. If `patch` is truncated for a large file, fall back to fetching the whole file at the PR's head ref: ```bash gh api "repos/modelcontextprotocol/modelcontextprotocol/contents/?ref=" \ --jq '.content' | base64 -d ``` ## Step 4: Extract RFC 2119 requirements Walk the added lines and identify sentences containing the keywords: **MUST**, **MUST NOT**, **SHOULD**, **SHOULD NOT**, **REQUIRED**, **SHALL**, **SHALL NOT**, **MAY**, **OPTIONAL**. **Quote the whole sentence**, not just the matched line. The matched word may sit inside a bullet point whose lead-in sentence supplies the keyword by inheritance — e.g.: > Servers SHOULD return standard JSON-RPC errors for common failure cases: > > - Resource not found: -32602 (Invalid Params) The bullet inherits `SHOULD`. The yaml row should quote the _combined_ obligation: `'Servers SHOULD return standard JSON-RPC errors for common failure cases: Resource not found: -32602 (Invalid Params)'` — see `src/seps/sep-2164.yaml` for the canonical example. **Regex alone is insufficient** (this is called out in Issue #243). Read for context: pronouns, "the server", and "such cases" all refer back to the lead-in. ## Step 5: Map severity → check vs. excluded From `AGENTS.md:50-56`: | Keyword | Severity | YAML field | | ---------------------------------------------- | -------- | -------------------------- | | MUST / MUST NOT / SHALL / SHALL NOT / REQUIRED | FAILURE | `check: sep--` | | SHOULD / SHOULD NOT | WARNING | `check: sep--` | | MAY / OPTIONAL | — | _no row — skip entirely_ | MAY / OPTIONAL sentences are noted in Step 4 only so you consciously skip them — they never produce a yaml row. A row is `excluded:` when a MUST/SHOULD requirement can't be protocol-observed by the harness. Do **not** write any `excluded:` row on your own authority — every exclusion goes through Step 6. While classifying, sort each MUST/SHOULD row into one of three buckets: - **`check:`** — observably testable on the wire. - **clearly-excluded** — you're confident it can't be observed (e.g. "clients SHOULD also accept -32002" when the harness only drives servers). - **borderline** — you'd default to `check:` but observability is questionable. Markers: - _Internal state_ — verbs like _record_, _store_, _associate_, _track_, _cache_. The harness sees wire traffic, not memory; usually only observable via a downstream row already in your list. - _UI / human-facing_ — _display_, _show_, _render_, _prompt the user_. - _Precondition phrasing_ — "Before doing X, the implementation MUST Y" where X is itself another row. Slug convention: lowercase-kebab, derived from the verb phrase. Examples from `sep-2164.yaml`: `no-empty-contents`, `error-code`. Same `id` is used for SUCCESS and FAILURE (`AGENTS.md:52`). ## Step 6: Confirm exclusions with the user Nothing becomes `excluded:` without sign-off. Two rounds: **Round 1 — clearly-excluded, single batch question.** One `AskUserQuestion` listing all clearly-excluded rows in the question body (slug + one-line reason each). Options: - `Exclude all as listed (Recommended)` - `Flip all to check:` - `Let me adjust per-row` — if chosen, append these rows to round 2. Skip this round if the bucket is empty. **Round 2 — borderline, one question per row.** One `AskUserQuestion` call with a question per borderline row (loop in batches of 4 if needed). For each: - header: the proposed slug - question: quote the requirement sentence + your one-line observability concern - options (list `check:` first — it's the default for borderline): - `check:` — keep as a testable check - `excluded: ` — drop to excluded with your stated reason - `merge into ` — offer when the row is a precondition for another row already in the list Apply the answers before writing. For any `excluded:` outcome, write the reason verbatim into the yaml and add an `issue:` URL if the user supplies one. A `merge` outcome means: drop this row, and append its `text:` to the surviving row's `text:` separated by `/` so the traceability isn't lost. ## Step 7: Rewrite the YAML Replace the two TODO rows the CLI generated with one row per extracted requirement. Preserve the CLI's quoting style (single quotes, two-space indent — see `src/seps/sep-2164.yaml`). **Key order within each row** — for `check:` rows the **`check:` key comes first**, then `text:`, then any optional `url:`. Scanning the left margin should reveal every check ID without reading the quoted sentences. For `excluded:` rows the order is **`text:` first**, then `excluded:`, then optional `issue:` — there's no ID to scan for, so lead with the requirement. **Row order in the file** — all `check:` rows first (in spec-diff order), then **all `excluded:` rows grouped at the bottom**, separated from the checks by **one blank line**. Do not interleave. ```yaml requirements: - check: sep-NNNN-first-slug text: '...' - check: sep-NNNN-second-slug text: '...' - text: '...' excluded: 'reason' issue: https://github.com/modelcontextprotocol/conformance/issues/ ``` If a requirement is ambiguous or you're not confident, leave it as a `TODO:` row rather than guessing — humans review this yaml before scenarios get written. Also fix the `spec_url`: the CLI emits the page URL with no anchor. If the requirements you extracted live under a specific spec subsection (e.g. `#error-handling`), append it. If a requirement comes from a **different spec page** than `spec_url` (the SEP touched multiple `.mdx` files — the CLI prints these as "PR also changes N other spec file(s)"), give that row a full `url:` override: ```yaml - check: sep-NNNN-slug text: '...' url: https://modelcontextprotocol.io/specification/draft/other/page#anchor ``` A row's effective spec reference is `row.url ?? file.spec_url`. Write the result back to `$YAML`. ## Step 8: Suggest a host scenario `AGENTS.md` prefers **fewer scenarios with more checks** over one-scenario-per-check. Before telling the user to write a new scenario, look for an existing one the new checks could be folded into. Determine the suite directory from the requirement subjects ("MCP clients MUST…" → `client/`, "Servers MUST…" → `server/`, "authorization servers MUST…" → `authorization-server/`; a SEP may map to more than one). Then search that directory for scenarios touching the same spec area: ```bash rg -l -i '|' src/scenarios// --type ts ``` Pick 2–3 domain terms from the SEP's subject matter (for a discovery SEP: `metadata`, `well-known`; for an auth-response SEP: `redirect`, `callback`, `pkce`). For each hit, pull the scenario's `name`/`description` to confirm relevance: ```bash rg -A1 'name:|description:' ``` If you find a plausible host, recommend it by path. If nothing fits, say so explicitly — a new scenario file is then the right call. ## Step 9: Hand-off Report to the user, in this order: 1. Path to the generated yaml. 2. Row counts: "`N check:` rows, `M excluded:` rows" — and note which exclusions the user signed off in Step 6. 3. Any requirements you left as `TODO:` and why. 4. **Host-scenario recommendation** from Step 8 — either "consider adding these checks to `src/scenarios//.ts` (it already exercises _X_)" or "no existing scenario covers this area; a new file is appropriate". 5. Remaining next steps the user owns: - add the checks to the host scenario (or create one) under `src/scenarios/{client,server,authorization-server}/`, - register any new scenario in `src/scenarios/index.ts` (`AGENTS.md:48`), - add a passing example to the everything-client/server and a negative test, per `AGENTS.md:74-81`. Do **not** generate or edit scenario `.ts` files or touch `src/scenarios/index.ts`. The skill's scope ends at the yaml plus the recommendation.