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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the description builds on that with useful behavioral details: automatic Halbtax/GA application and mobile app deep-linking. No contradictions with 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?

Three sentences, each serving a clear purpose: function, usage condition, and platform behavior. No redundancy or fluff.

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 description covers the tool's purpose, when to use it, and key behavioral nuances. With a fully documented schema and annotations, this is sufficient for an agent to select and invoke it correctly, though it does not explicitly state the return format (a link is implied).

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?

All 9 parameters are fully documented in the schema (100% coverage), so the description does not need to explain them. It adds a minor note about Halbtax/GA being applied automatically, which aligns with the reduction_card parameter, but no further parameter-specific insight.

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'. It uses a specific verb and resource, and the focus on 'buy' distinguishes it from sibling tools like search_connections or get_prices.

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 phrase 'Only call this when the user wants to buy a specific ticket' provides an explicit usage condition. It does not explicitly name alternative tools, but the condition implies this is for purchase scenarios rather than searching or pricing.

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