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

With no annotations, the description carries the full disclosure burden. It does disclose the key side effect (a new chat thread is created), but says nothing about auth/permissions, failure modes when a thread already exists, or rate/duplicate-message constraints.

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?

Two short sentences, zero filler, with the action and its effect front-loaded before the sequencing note.

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?

Adequate for a simple 4-parameter tool, but with no annotations and no output schema the description never says what the call returns or how duplicate-thread situations are handled. Params are fully documented by the schema, which keeps this from being worse.

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 the schema already explains every parameter, including where advert ids and user_ids come from. The description only adds that ids originate from search_suggest, which is marginal added meaning; baseline 3 applies.

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?

States a specific verb and resource ('Send the first message to a seller about a listing') and clarifies the effect ('opens a new Jiji chat thread'). The 'first message' framing implicitly distinguishes it from send_reply and view_chat_thread in the sibling set.

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?

'Use after search_suggest with listing ids' gives an explicit prerequisite and sequencing hint. No negative guidance (e.g. what to do if a thread already exists, or when to use send_reply instead), so it falls short of a 5.

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