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

Annotations already declare readOnlyHint=true and destructiveHint=false. The description supplements this with valuable behavioral context: 'On mobile with SBB app installed, opens directly in the app with Halbtax/GA applied automatically.' This discloses environment-dependent behavior and automatic discount handling beyond what annotations provide.

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?

The description is two sentences long, front-loaded with the core purpose, and every clause earns its place. It includes a usage condition and a behavioral note with no redundancy.

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?

The tool has 9 parameters and no output schema, but the schema covers param semantics and annotations cover safety. The description adds usage timing and a key environmental behavior. Missing details like desktop behavior or link expiration are minor gaps, so it is adequately complete for the tool's complexity.

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 baseline is 3. The description does not add parameter-specific semantics beyond what the schema already provides. It mentions Halbtax/GA applied automatically, which slightly relates to reduction_card, but this is behavioral context rather than parameter explanation.

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 clearly states the tool's function: 'Get a direct purchase link to buy a train ticket on SBB.ch.' The verb 'get' and resource 'direct purchase link' are specific. It also distinguishes from siblings like search_connections and get_prices by noting 'Only call this when the user wants to buy a specific ticket.'

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?

The description provides explicit usage context: 'Only call this when the user wants to buy a specific ticket.' This clearly indicates when the tool is appropriate and implicitly excludes non-purchase scenarios. It doesn't name alternatives explicitly, but it gives a clear condition for use.

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