Borrowing it
Nothing to install: this file belongs to webhook-co/webhook. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/webhook-co/webhook/main/.cursor/skills/build-mcp-server/SKILL.mdgit clone --depth 1 https://github.com/webhook-co/webhookWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/webhook-co/webhook/build-mcp-server)<a href="https://agentmods.dev/skills/webhook-co/webhook/build-mcp-server"><img src="https://agentmods.dev/badge/skills/webhook-co/webhook/build-mcp-server/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/webhook-co/webhook/build-mcp-server"><img src="https://agentmods.dev/badge/skills/webhook-co/webhook/build-mcp-server.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00047 | $0.00960 |
| Opus 5.5 | $0.00019 | $0.00384 |
| Sonnet 5.5 | $0.00009 | $0.00192 |
| Haiku 4.5 | $0.00005 | $0.00096 |
Grade A, and why
build-mcp-server scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 76 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Build MCP server
MCP is a first-class, non-negotiable surface here: every capability is reachable identically from
CLI / API / web / MCP, and the MCP server ships as a real product surface (including the
webhook → agent trigger), not an afterthought. New work lives in apps/mcp and reuses the same
shared/ types as the other surfaces — never invent an MCP-only payload shape.
Work through five phases. Don't skip to scaffolding.
Phase 1 — interrogate the use case
Before any code, get crisp answers:
- What capability is being exposed, and does it already exist on CLI/API/web? If so, mirror its contract; if not, design for all four surfaces from the start (parity is the rule).
- Who calls it — an interactive agent, an automation, the webhook → agent trigger? What's the auth and tenant context? (Tenant isolation is enforced by Postgres RLS; the MCP layer must carry tenant identity, never bypass it.)
- What data crosses the boundary, and does any of it carry PII/PHI or raw payloads? Raw payloads live in R2 and are referenced by event id — don't pull bodies through MCP tool output.
Phase 2 — recommend a deployment model
State a recommendation, don't list every option:
- Remote streamable-HTTP on Workers (default here). Our stack is TypeScript on Cloudflare Workers; host the MCP server as a Worker so it shares auth, bindings, and observability with the rest of the platform. This is the right answer for almost everything.
- Elicitation when a tool needs to ask the user for a missing input mid-call.
- MCP app (interactive UI) only when a widget genuinely beats text — see
build-mcp-app, and respect the human-UI-testing hard stop. - MCPB bundle only for a local stdio server a user installs on their machine — see
build-mcpb. - Local stdio only when the tool must touch the user's local environment (e.g. the CLI tunnel); otherwise prefer remote.
Phase 3 — select a tool-design pattern
- One tool per action for a small, stable capability set — clearest for the model and the user.
- Search + execute when wrapping a large or open-ended API: a
search/listtool to discover, then a focusedexecutetool, so the model isn't drowning in dozens of near-duplicate tools. - Name tools for intent, validate every input at the boundary with a schema, and return typed, actionable errors — never leak stack traces, secrets, or tenant data in tool output.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 1mo ago First seen · 76 lines · 47 tokens per session scan A 85bee513e588
build-mcp-server is a skill published in the GitHub repository webhook-co/webhook (0 stars, last pushed 18d ago), licensed Apache-2.0. It adds 47 tokens to every session and 960 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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