Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/webhook-co/webhook/build-mcp-servernpx skills add webhook-co/webhook --skill build-mcp-servergit clone --depth 1 https://github.com/webhook-co/webhookWhat 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 | $0.00047 | $0.00960 |
| Opus 5 | $0.00023 | $0.00480 |
| Sonnet 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 2d 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.
- 2d 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 7d ago), licensed Apache-2.0. It adds 47 tokens to every session and 960 once invoked, about $0.0002 per session on Opus 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.
Other skills, from other repositories
flaim-fantasy
Use when a user wants analysis of a Flaim-connected ESPN, Yahoo, or Sleeper fantasy league, or help with Flaim setup, capabilities, or permissions. This includes rosters, standings, matchups, available players, transactions, historical seasons, and lineup, waiver, or trade advice. Do not use for generic sports news…
mcp-migration
Diagnose and carry out the migration of an MCP server to the 2026-07-28 specification — the revision that made the transport stateless, formalized OAuth 2.1, and deprecated the logging, sampling, and roots capabilities. Use this skill whenever someone mentions migrating, upgrading, or checking an MCP server against…
activity-brief
Give a time-bucketed league activity briefing on recent fantasy moves, including who moved who, when, and why. Use when the user explicitly wants a transaction roundup or invokes /activity-brief.
analyze-matchup
Analyze the current fantasy matchup with scores, remaining players or games, and a fact-based forecast. Use when the user explicitly wants a matchup-state breakdown or invokes /analyze-matchup.
gw1-build-assistant
Use when the user asks about Guild Wars 1 (the original 2005 game, not GW2) — designing or reviewing skill bars, decoding or producing template codes (strings like "OgCjkurIrSuXaXPXBYihygvlYcA"), hero team composition, skill lookups or comparisons, or pasting a paw-ned2 team blob ("pwnd0001..."). Use the gw1-mcp tools…
sandbox-sdk
Build sandboxed applications for secure code execution. Load when building AI code execution, code interpreters, CI/CD systems, interactive dev environments, or executing untrusted code. Covers Sandbox SDK lifecycle, commands, files, code interpreter, and preview URLs. Biases towards retrieval from Cloudflare docs…