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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint, and openWorldHint, covering the safety profile. The description adds useful domain semantics (values are repos with at least one event, mirrors GET /api/events/facets) but says nothing about result size, pagination, or how the date-range filter affects the returned set.

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 purpose, followed by scope and the routing hint. Three compact clauses with no filler, though the REST-endpoint note is slightly redundant for an agent that cannot call the endpoint directly.

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?

For a read-only enumeration tool with no output schema and rich annotations, the description conveys purpose, scope, and intended workflow well. The main gap is undocumented parameter semantics (source_id) and any notion of result cardinality.

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 0%, so the description must carry parameter meaning. It explains attr (the facet, currently only 'repo') and implies the date-range params, but source_id is never explained in either the schema or the description, and no date format is given.

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?

States a specific verb and resource: list the distinct values of a faceted event metadata field. It immediately scopes the operation ('currently just "repo"') and ties it to a known surface (the Event Explorer repo picker), letting an agent distinguish it from query_events 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?

Explicitly names the alternative and the condition that selects it: use this to discover query_events' meta_repo filter values before calling query_events. The relationship between the two sibling tools and the ordering of calls is left to no inference.

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