What is mcp-tool-builder?

A guide to building custom tools that AI clients can call through hosted MCP servers, using Salesforce Apex, Flows, named queries, or prompt templates.

It is for exposing Salesforce backend actions, Flow-based tools, query APIs, and reusable prompts to clients such as Claude, ChatGPT, and Cursor.

It explains which tool design fits the job and highlights that MCP and Agentforce use different ways to coordinate work.

mcp-tool-builder — Skill for Claude Code by divingsbysangam

Install

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.

Any agent

npx skills add divingsbysangam/salesforce-compound-engineering-plugin --skill mcp-tool-builder

Clone the repo

git clone --depth 1 https://github.com/divingsbysangam/salesforce-compound-engineering-plugin

Made for: Claude Code.

Or install sf-compound-engineering, the plugin that ships this one along with the rest of its 68 skills, 1 hook, 2 MCP servers.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/skills/divingsbysangam/salesforce-compound-engineering-plugin/mcp-tool-builder/github.svg)](https://agentmods.dev/skills/divingsbysangam/salesforce-compound-engineering-plugin/mcp-tool-builder)

Your own site

<a href="https://agentmods.dev/skills/divingsbysangam/salesforce-compound-engineering-plugin/mcp-tool-builder"><img src="https://agentmods.dev/badge/skills/divingsbysangam/salesforce-compound-engineering-plugin/mcp-tool-builder/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.

Your own site · 80×15

<a href="https://agentmods.dev/skills/divingsbysangam/salesforce-compound-engineering-plugin/mcp-tool-builder"><img src="https://agentmods.dev/badge/skills/divingsbysangam/salesforce-compound-engineering-plugin/mcp-tool-builder.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 34 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 519 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

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	$0.00034	$0.00519
Opus 5	$0.00017	$0.00260
Sonnet 5	$0.00007	$0.00104
Haiku 4.5	$0.00003	$0.00052

Measured 8d ago against content hash 88ed6d420379, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

mcp-tool-builder 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 8d 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.

skills/mcp-tool-builder/SKILL.md · 38 lines

How it starts

The opening of the file, as written. The whole thing — 38 lines — stays where its author put it; the contents beside it link to each section on GitHub.

MCP Tool Builder

SCOPE: HOSTED_MCP - This skill applies to building custom tools for Salesforce Hosted MCP Servers. Use when: Creating Apex @InvocableMethod actions, Flow-based tools, Named Query APIs, or prompt templates for MCP exposure.

Custom MCP servers expose backend logic as tools that AI clients (Claude, ChatGPT, Cursor) can invoke.

CRITICAL WARNING: MCP and Agentforce use fundamentally different orchestration models. Code designed for Agentforce will break on MCP unless adapted. See "MCP vs Agentforce Architecture" section.

Required reads

Procedure lives in sibling files, not only in this orchestrator:

Tool Types — read references/tool-types.md before acting on this section.
Apex Invocable Action Tools — read references/apex-invocable-action-tools.md before acting on this section.
MCP vs Agentforce Architecture — read references/mcp-vs-agentforce-architecture.md before acting on this section.
Flow-Based MCP Tools — read references/flow-based-mcp-tools.md before acting on this section.
Named Query API Tools — read references/named-query-api-tools.md before acting on this section.
Prompt Templates for MCP — read references/prompt-templates-for-mcp.md before acting on this section.
Recommended Resolution — read references/recommended-resolution.md before acting on this section.
Similar Resolved Cases — read references/similar-resolved-cases.md before acting on this section.
Confidence: High — read references/confidence-high.md before acting on this section.
Retrieved Data (merge fields here) — read references/retrieved-data-merge-fields-here.md before acting on this section.
Your Task — read references/task.md before acting on this section.
Custom Server Registration — read references/custom-server-registration.md before acting on this section.
Testing MCP Tools — read references/testing-mcp-tools.md before acting on this section.
Tool Description Best Practices — read references/tool-description-best-practices.md before acting on this section.

Read the full file on GitHub · 38 lines

Files

What ships with it

15 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.

Changes

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.

8d ago First seen · 38 lines · 34 tokens per session scan A 88ed6d420379

Subscribe to this mod's changes

mcp-tool-builder is a skill published in the GitHub repository divingsbysangam/salesforce-compound-engineering-plugin (10 stars, last pushed 4d ago), licensed MIT. It adds 34 tokens to every session and 519 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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