Service Status

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

With no annotations, the description carries the full burden and does meaningful work: it discloses the data provenance ("the TTC's own site endpoints"), an accuracy caveat ("best effort"), and a freshness field (as_of) that lets the agent judge staleness. It does not mention auth, rate limits, or caching, but for a zero-parameter read tool this is solid disclosure.

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 usage guidance is front-loaded in the first clause, then the payload contents are listed in a scannable semicolon series with zero filler. It is a single long sentence and slightly run-on, which costs it a point, but every clause names a distinct returned artifact.

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?

An output schema exists, so the description need not explain return shapes, yet it still sketches the major sections so the agent knows what to expect. Combined with the best-effort caveat and freshness field, an agent has enough to call it and interpret results, with only minor gaps around data recency guarantees.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate and the baseline of 4 applies. The schema is empty with additionalProperties false, consistent with the description implying a global, unfiltered snapshot.

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 enumerates concrete resources returned (subway closures as station spans, suspended/detoured surface routes with skipped-stop counts, reduced speed zones, elevator/escalator outages, counts and as_of), so an agent knows exactly what this returns. It positions itself as the entry point ahead of siblings like alerts, detours and service_changes, 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?

"The first call for any trip or 'what's going on' question" gives an explicit trigger condition and tells the agent to prefer this over the narrower siblings. It stops short of stating when-not-to-use or naming which sibling to fall back on for a specific sub-question.

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