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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false. The description adds useful behavioral detail beyond that: it searches both personal and collected address books, ignores case and accents, and returns name, addresses, phones, and source book. It does not discuss rate limits or permissions, but those are less critical for a local read-only search.

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 tightly written sentences with no waste. The scope and search behavior are front-loaded, followed by the return contents, making it easy to parse quickly.

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 local search tool with full schema descriptions, clear annotations, and an output schema, the description is complete enough to call correctly. It covers scope, matching behavior, and return fields without needing to duplicate structured metadata.

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 nevertheless adds meaning beyond the schema by clarifying that `query` is matched against name, company, addresses, and phone numbers, and that matching ignores case and accents. It does not add information about `limit` or `profile` beyond the schema, keeping it from a 5.

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 uses a specific verb ('Searches') and resource ('Thunderbird's address books on this computer'), and explicitly distinguishes local Thunderbird books from other contact sources by naming the personal and collected address books. It also states the searchable fields and return contents, so an agent can identify it without opening the 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?

The description clearly establishes the context: local Thunderbird address books, not cloud or other account-based contact stores. It does not explicitly name alternatives like search_contacts or m365_search_contacts or state when not to use this tool, but the Thunderbird-local framing provides strong implicit routing.

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