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

Annotations already declare non-read-only, idempotent, non-destructive, closed-world behavior, so the description only needs to add context — and it does: it clarifies the digest is folded into a single daily summary e-mail (never two a day), that consent is required, and that every e-mail carries a one-click unsubscribe. These are real behavioral facts not present in the structured fields, though the effect on an existing subscription's frequency is unstated.

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

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

Three tight sentences, front-loaded with the on/off action, followed by the two trust-relevant facts (no unsolicited subscription, one-click unsubscribe). No filler sentences, though the parenthetical '(or off)' is slightly redundant with the subscribe parameter.

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

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

This is a low-complexity two-parameter tool with an output schema, so the description need not explain return values. It covers the action, the delivery mechanism, consent, and opt-out, leaving only minor edge cases (frequency ignored on unsubscribe, overwriting an existing subscription) unaddressed.

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

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

Schema description coverage is 100%, so both parameters (subscribe boolean, frequency enum with 'Default daily.') are already documented. The description adds only the daily/weekly framing, which is largely redundant with the enum; it does not explain how frequency behaves when subscribe is false.

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

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

The description names a concrete verb pair ('turns on (or off)') and a concrete resource ('the e-mail with today's opportunities for the connected account'), so the action is unambiguous. It does not name the sibling it complements (jt_today, which presumably returns the same opportunities on demand), so the differentiation is only implied.

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

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

Usage is implied rather than stated: an agent can infer this is the tool for opting into the daily/weekly digest, and 'records the user's own choice: nobody is subscribed without asking' hints at consent preconditions. There is no explicit 'use this when X, use jt_today when Y' routing, and no mention of what happens if a subscription already exists.

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