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

Annotations already declare destructiveHint=true, readOnlyHint=false, openWorldHint=true, and idempotentHint=false, so the safety profile is covered. The description adds nothing behavioral — it doesn't warn that each call creates a separate persistent session (non-idempotent) or that this may consume quota/credits, which would be useful context beyond the annotations.

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?

Two sentences, front-loaded with the action; the second sentence usefully previews outputs since there is no output schema. The 'provide a seed topic or URL' clause slightly overlaps the schema but is not wasteful.

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 correctly summarizes what the session yields (related keywords, volumes, clustering), and a required description of mutation semantics is partly carried by the destructive annotation. It could better note that sessions persist and are individually addressable (get_keyword_session/list_keyword_sessions), but it is adequate for a 4-parameter creation tool.

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 topic, country, site_id, and language are all documented in the schema. The description only mentions a seed topic or URL, adding no syntax, defaults, or format details beyond what the schema provides. Baseline 3 applies.

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 (start a keyword research session) and names the outputs (related keywords, search volumes, clustering). It does not explicitly distinguish itself from siblings like keyword_chat, get_keyword_session, or seed_keywords_from_gsc, but the core purpose is unambiguous.

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 says what seed input to provide but gives no when-to-use guidance, no prerequisites, and no mention of alternatives such as keyword_chat or list_keyword_sessions. The agent must infer context from the name alone.

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