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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the description's real contribution is behavioral: the truncation rule (only the most recent `event_limit` events, 40 by default, `events_total` gives the full count) and the eta_revisions shape (previous/new date plus slip in seconds). It omits anything about auth, quotas, or ordering caveats, but for a read tool the truncation semantics are the key disclosure and they are present.

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?

Front-loaded with the core capability, then usage triggers, then return detail, then the routing exclusion. Dense and largely waste-free, though the quoted example-utterances list is longer than strictly necessary.

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?

With no output schema, the description carries the burden of describing returns and does so: route legs, ordered events with place/time/coordinates, eta_revisions with previous/new dates and slip seconds, plus the map rendering for MCP Apps clients. Nothing essential to correct invocation is missing.

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 coverage is 100%, so the baseline is 3; the description goes beyond the schema by explaining what `event_limit` actually does (windows the most recent events) and pairing it with the `events_total` counter that reports the unfiltered count. That is meaningful semantics an agent could not derive from the schema alone.

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?

Opens with a specific verb+resource scope ('The journey of one shipment') and enumerates the payload components (route legs, events, eta revisions). It also explicitly names the sibling it is not — search_shipments' `latest_event` — so an agent can distinguish it without opening either schema.

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?

Provides concrete triggering phrasings ('what happened to shipment shp_123', 'has the ETA moved') plus an explicit when-not: for a list of shipments, use search_shipments' `latest_event` rather than calling this per shipment. Both the use case and the anti-pattern are stated.

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