Borrowing it
Nothing to install: this file belongs to pvliesdonk/markdown-vault-mcp. 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/pvliesdonk/markdown-vault-mcp/main/.agents/skills/designing-tool-outcomes/SKILL.mdgit clone --depth 1 https://github.com/pvliesdonk/markdown-vault-mcpWrote 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/pvliesdonk/markdown-vault-mcp/designing-tool-outcomes)<a href="https://agentmods.dev/skills/pvliesdonk/markdown-vault-mcp/designing-tool-outcomes"><img src="https://agentmods.dev/badge/skills/pvliesdonk/markdown-vault-mcp/designing-tool-outcomes/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/pvliesdonk/markdown-vault-mcp/designing-tool-outcomes"><img src="https://agentmods.dev/badge/skills/pvliesdonk/markdown-vault-mcp/designing-tool-outcomes.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 | $0.00070 | $0.02213 |
| Opus 5.5 | $0.00028 | $0.00885 |
| Sonnet 5.5 | $0.00014 | $0.00443 |
| Haiku 4.5 | $0.00007 | $0.00221 |
Grade A, and why
designing-tool-outcomes 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 26d 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 — 152 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Designing tool outcomes
A tool call ends in one of four outcomes. Classify each case before you write
its code. The class fixes three things at once: what the model receives, what
the message tells it to do next, and the log level. The evidence behind every
rule is in docs/design/reference/mcp-tool-outcomes-and-errors.md and
docs/design/reference/negative-outcomes-and-faults.md.
The four outcomes
The contract is what the tool's description and return type promise. An
outcome that fits the contract is a result. An outcome that cannot produce the
promised thing is an error, however ordinary it is. The two texts split the
work: the description states the contract, limits that hold for every call
included, and never lists failures (writing-model-facing-text, "The
contract, not the failures"). So the error text is the one place a failure
is explained, and it has to stand on its own.
| # | Outcome | Examples | Code | The message tells the model | Log |
|---|---|---|---|---|---|
| 1 | Contract met | the note's text; an empty list from a search that ran to completion | return the value |
nothing extra | the middleware's completion line |
| 2 | Change the request | no note at that path; invalid input; path outside the store; write refused until if_match is passed; a feature this deployment leaves off (a read-only vault, an opt-in feature not enabled) |
raise ToolError(msg, log_level=logging.INFO) |
what was wrong and what to call or pass instead; repeating the same call will not help | INFO |
| 3 | Refresh, then retry | stale version or etag; conflicting concurrent change | raise ToolError(msg, log_level=logging.INFO) |
read again, reapply the change, retry with the new token | INFO |
| 4 | The server failed | I/O error; permissions on the server's own files; a stored file the server cannot parse; index or dependency unavailable; required configuration left out; a bug | let it reach the boundary, or raise ToolError(msg) after logging |
the request was fine; retry later (transient) or tell the user (needs an operator); do not change strategy | WARNING if it heals itself, else ERROR with the traceback |
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.
- 26d ago Changed · +16 lines c11df839a833
- 27d ago First seen · 136 lines · 70 tokens per session scan A bc6c01e5e33a
designing-tool-outcomes is a skill published in the GitHub repository pvliesdonk/markdown-vault-mcp (35 stars, last pushed today), licensed MIT. It adds 70 tokens to every session and 2,213 once invoked, about $0.0003 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 2026-09-26.
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