Borrowing it
Nothing to install: this file belongs to tyler-mitchell/type-atlas. 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/tyler-mitchell/type-atlas/main/.skills/usage-first-mcp-development/SKILL.mdgit clone --depth 1 https://github.com/tyler-mitchell/type-atlasWrote 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/tyler-mitchell/type-atlas/usage-first-mcp-development)<a href="https://agentmods.dev/skills/tyler-mitchell/type-atlas/usage-first-mcp-development"><img src="https://agentmods.dev/badge/skills/tyler-mitchell/type-atlas/usage-first-mcp-development/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/tyler-mitchell/type-atlas/usage-first-mcp-development"><img src="https://agentmods.dev/badge/skills/tyler-mitchell/type-atlas/usage-first-mcp-development.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 | $0.05141 |
| Opus 5.5 | $0.00019 | $0.02056 |
| Sonnet 5.5 | $0.00009 | $0.01028 |
| Haiku 4.5 | $0.00005 | $0.00514 |
Grade A, and why
usage-first-mcp-development 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 — 400 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Usage-First MCP Development
The work
You are trying to understand a codebase. Really trying — there is something you need to know to make the next change correctly, and you do not know it yet.
The instrument you use to find out is the one you are building.
That is the whole method. Not a process to execute: a situation to be in. Do real work, need real answers, and pay attention to what happens when you ask.
An agent that treats this as a task sheet produces exactly what a task sheet produces — locally valid changes, no design, and a tool that nobody can think with. The rails at the end of this document are cheap insurance against specific expensive mistakes. They are not the point, they are not the shape of the work, and narrating them is worse than useless. Follow them invisibly.
What "good" means here
The product is not a function call. It is the answer an agent receives and has to act on.
So the bar is ergonomic, and it is answered by imagining a competent agent that did not write any of this:
They asked a question because they were stuck. Does this answer unstick them, or do they now have to open a file, ask again with different arguments, or guess?
An answer that is correct and leaves them stuck has failed. Every reformulation they are forced into is a defect you caused.
Everywhere else you have worked, your tools were trustworthy and the code was suspect. Here the tool is the code, and a malformed answer does not announce itself — it arrives looking like an answer and you act on it. Which is why: source, types, and tests say what the code says; only a call says what an agent receives. Claims about behaviour need a call behind them.
One boundary on that rule, learned the hard way. It governs the MCP surface —
what an agent receives. For the substrate beneath it — Volar, TypeScript, the
bridge — the repo's recorded evidence outranks your live probe:
docs/volar-affordance-evidence.md says what was true, and instrumentation
only says what changed. A substrate diagnosis built from probes alone was
confidently wrong here for ten days, while the observation contradicting it
sat unread in the ledger the whole time. Read the ledger first, and when it
disagrees with a live call, you have found a change, not a refutation.
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 · 400 lines · 47 tokens per session scan A f2631cff0497
usage-first-mcp-development is a skill published in the GitHub repository tyler-mitchell/type-atlas (2 stars, last pushed 1mo ago), licensed Apache-2.0. It adds 47 tokens to every session and 5,141 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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