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

Annotations already declare read-only, idempotent, non-destructive, closed-world behavior, and the description adds real operational context on top: holiday Thursdays are silently omitted, dinners are weekly on Thursday 19:30 London time, and the booking window opens two weeks prior Wednesday and closes Tuesday 23:59. These are non-obvious behaviors an agent could not infer from the schema or annotations.

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?

Front-loaded with purpose and defaults; the booking-window and holiday-omission sentences each carry actionable information. The clause about 'small groups of strangers who want to make friends' is atmospheric rather than functional and is the only sentence that doesn't earn its place.

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?

Covers defaults, timezone, maximum horizon, weekly cadence, omitted holiday weeks, and booking timing -- everything needed to call and interpret this zero-required-param list tool. An output schema exists, so the absence of return-value detail is not a gap.

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 coverage is 100%, so baseline is 3, but the description adds meaning the schema lacks: that dates are interpreted against the London-time Thursday cadence and the booking window, explaining why a caller would narrow the range. The city restriction ('only London has dinners') is already duplicated in the schema description, so the incremental gain is modest rather than decisive.

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?

Opens with a specific verb and resource ('Lists upcoming Siena friendship dinners in a city between two dates') plus the value-add of showing which are bookable. The plural list framing cleanly separates it from the singular get_dinner sibling without needing to name it.

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?

Gives concrete guidance on defaults ('with no dates, the tool lists the next 4 Thursdays') and horizon ('up to 12 weeks ahead'), which tells the agent when to supply dates vs. omit them. It never explicitly routes to get_dinner or start_booking as alternatives for a specific result or to book, so the when-vs-sibling element is only implied.

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