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

The description discloses key behavioral traits beyond annotations: computed once per day after midnight, includes build timestamp, unavailable after restart. These add value since annotations only indicate read-only and idempotent.

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 concise (3-4 sentences), front-loaded with purpose, and every sentence provides essential information: output format, update frequency, guidance, and availability. No wasted words.

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 is fully complete for a simple tool: explains output (rank, name, minutes, URL), update cadence, and behavioral quirks (unavailable after restart). No output schema needed as format is described.

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?

With zero parameters and 100% schema coverage, the description adds the confirmation 'Takes no arguments' and explains the output format. Baseline is 4, and the description meets that with no gaps.

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 it returns the ten UK level crossings with the most predicted road-closed time today. It uses specific verbs ('gives') and identifies the resource (level crossings), and distinguishes from sibling tools like crossing_status.

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 explicitly guides when to use this tool vs. crossing_status: 'it is a whole-day total, not a live reading, so use crossing_status for what a barrier is doing now.' It also notes unavailability after restart.

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