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

Annotations already declare the safety profile (readOnlyHint=false, destructiveHint=false, openWorldHint=true, idempotentHint=false). The description adds non-obvious behavior: the 15-minute duration, that exactly one call is booked, and that Google emails the invite with a Meet link to the given address — an external side effect the annotations don't convey.

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 short sentences, front-loaded with the core action, then the precondition, then the side effect. No filler and nothing repeated from the schema or annotations.

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?

For a mutating booking tool with no output schema, the description covers the action, the precondition, and the resulting external email. It omits failure behavior (e.g., slot already taken) and the meaning of the language parameter, which are minor given the tool's simplicity.

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 only 33% (only topic and slot_start documented), so the description must compensate. It clarifies that slot_start must be an open slot and ties the email parameter to the invite delivery, but company, language, and name remain undocumented in both places.

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 concrete verb and resource with scope: 'Books one 15-minute video call in an open slot.' This clearly separates it from get_open_slots (read-only slot listing) and about_wirstartenki, though it never names those siblings explicitly.

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 a real precondition for invocation: 'Only after the person confirmed the time and their e-mail.' Combined with 'in an open slot' it implies the get_open_slots prerequisite, but it never explicitly routes the agent to that sibling or states exclusions.

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