jef-mcp

Ask Jef yes or no

jef_yes_no

Read-onlyIdempotent

Get a definitive YES or NO with a confidence score to settle subjective dilemmas—like whether to go out, send a message, or deploy on Friday. Do not use for factual questions.

Instructions

Answer a yes-or-no question with YES or NO and a confidence. Use this when the user wants a question settled and there is no correct answer, such as whether to go out, whether to send the message, or whether to deploy on a Friday. Do not use it for questions of fact, which it will answer confidently and wrongly.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`question`	Yes	The question, phrased so that yes or no is a sensible answer. It is hashed rather than read, so wording changes the answer but meaning does not.

Output Schema

TableJSON Schema

Name	Required	Description
`kind`	No	Which decision shape was used.
`answer`	Yes	Exactly "YES" or "NO", or "ESCALATED TO A HUMAN", or "NOT EVALUATED".
`blocked`	Yes	True when the input contained profanity, slurs or sexual content. Nothing was stored or echoed. Do not retry.
`ranking`	No	The options in order, best first. Null unless the shape was order.
`cost_usd`	No	Always 0. There is no billing.
`thoughts`	No	Always 0.
`escalated`	Yes	True when the input touched health, harm, money, law or safety. Tell the person to ask a human. Do not rephrase and retry.
`confidence`	Yes	0.84 to 0.99 normally, exactly 0 when escalated or blocked. It is not calibrated and means nothing.
`latency_ms`	No	Negative. Jef answers before you ask.
`tokens_read`	No	Always 0. The input is hashed, not read.
`probabilities`	No	One entry per option, percentages summing to 100. Null unless the shape was pick.

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.4.7Sep 19, 2026

TDQS

A4.3/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering the safety profile. The description adds a valuable behavioral caveat—that it will answer factual questions 'confidently and wrongly'—which is beyond what annotations provide. The schema note about hashing also contributes, but that is not part of the main description.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is exactly two sentences with zero fluff. It front-loads the core purpose first, then provides usage guidance and a critical warning. Every word earns its place, and it remains highly readable.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a low-complexity tool with a single parameter and an existing output schema, the description is complete. It covers purpose, when to use, when not to use, and a behavioral caveat. The output format is presumably handled by the output schema, so nothing essential is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the 'question' parameter is fully documented in the schema, including the hashing behavior and constraints. The main description adds no additional parameter-level semantics, so the baseline of 3 applies as the schema does the heavy lifting.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb ('Answer'), a clear resource ('a yes-or-no question'), and the exact output format ('YES or NO and a confidence'). It distinguishes itself from sibling tools by restricting scope to questions with no correct answer and explicitly excludes factual questions, making it unambiguous which tool to pick.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It explicitly says when to use it ('when the user wants a question settled and there is no correct answer') with concrete examples, and when not to ('Do not use it for questions of fact'). However, it does not name any alternative sibling tools (e.g., jef_score or jef_pick) that might apply instead, so the alternatives component is missing.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

Deploy Server