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 skills add celigo/ai --skill building-mcp-serversgit clone --depth 1 https://github.com/celigo/aiWrote 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/celigo/ai/building-mcp-servers)<a href="https://agentmods.dev/skills/celigo/ai/building-mcp-servers"><img src="https://agentmods.dev/badge/skills/celigo/ai/building-mcp-servers/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/celigo/ai/building-mcp-servers"><img src="https://agentmods.dev/badge/skills/celigo/ai/building-mcp-servers.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- Socket pass
- Snyk pass
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 | $0.00046 | $0.03637 |
| Opus 5 | $0.00023 | $0.01818 |
| Sonnet 5 | $0.00009 | $0.00727 |
| Haiku 4.5 | $0.00005 | $0.00364 |
Grade A, and why
building-mcp-servers 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 9d 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 — 231 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Building MCP Servers
An MCP server is a Model Context Protocol endpoint that exposes Celigo Tools and builder-mode APIs as callable tools for external AI agents and MCP clients. Concerns when building an MCP server:
- Endpoint identity -- unique
relativeURIthat forms the server's URL path - Tool selection -- which Tool resources to expose, each with an MCP-compatible name
- API selection -- which builder-mode API resources to expose (script-mode APIs are not supported)
- Annotations -- MCP-standard behavior hints (
readOnlyHint,destructiveHint,idempotentHint,openWorldHint) that help AI agents decide when and how to call a tool - Overrides -- per-server customization of a tool's connections, exports, imports, and routers without modifying the underlying tool definition
- Name uniqueness -- tool names must be unique across all
tools[]andapis[]entries within the server
MCP servers support configurable authentication of their own -- Celigo OAuth (the default), an external IdP, or static API tokens, gated by mcp:read / mcp:write scopes (see Authentication and Scoping). Outbound calls to external systems use the connections referenced by the underlying tools and APIs.
Used alongside tools and APIs. The MCP server is a thin exposure layer -- all processing logic lives in the referenced Tool and API resources.
Composition Patterns
MCP servers combine two types of entries:
Tool Entries (tools[])
Reference Celigo Tool resources. Each tool becomes an MCP tool endpoint. The tool's input.schema must have type: "object" at the root to comply with the MCP specification. Tool entries support annotations (behavior hints) and overrides (per-server connection/resource customization).
API Entries (apis[])
Reference Celigo builder-mode API resources. Each API becomes an MCP tool endpoint. Only type: "builder" APIs are supported -- script-mode and legacy APIs cannot be exposed via MCP. API entries do not support annotations or overrides.
What ships with it
6 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 9d ago First seen · 231 lines · 46 tokens per session scan A c7fe85d231e7
building-mcp-servers is a skill published in the GitHub repository celigo/ai (3 stars, last pushed yesterday), licensed MIT. It adds 46 tokens to every session and 3,637 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.
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