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

Annotations already cover safety (readOnly, idempotent, openWorld), so the bar is lower; the description adds useful behavioral context beyond them: the CMS-only scope, the implicit run-range defaulting for a dataset recid, and the variant defaulting rules. It stops short of noting rate limits or how large a returned list can be, so it is not exhaustive.

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?

It is a dense block but front-loads the core purpose and then the selection rules in a logical progression; every clause carries information. It is slightly long for the amount of guidance and could be split into sentences for faster scanning.

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 an output schema present the description needn't explain return values, but it still summarizes them (runs with luminosity-section ranges and list file download URL). Combined with annotations and full schema coverage, an agent has everything needed to call it correctly.

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 100%, so the baseline is 3, but the description adds interpretive value: it clarifies the dual meaning of recid (collision dataset vs named list) and how variant and run bounds default differently per selection mode.

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 names a specific verb and resource ('Get a CMS validated-run (good-run) list') and immediately states what the artifact certifies (luminosity sections good for physics), which no sibling tool does. It is clearly distinguishable from the record/file/reference lookup siblings.

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?

It states the mutually exclusive selection rules explicitly ('give exactly one of recid and run_period'), explains the variant choice, and routes the agent to a sibling ('cern_opendata_list_reference with topic run_periods lists them') for discovering run periods. That is concrete when/how guidance, not inference.

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