List Contacts

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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so safety is covered. The description adds non-obvious behavioral context: exact-match lookup semantics for identifiers versus audience filtering, and a presentation rule about not surfacing ids/timestamps unprompted. It stops short of describing pagination or result-size behavior, which the schema partially covers.

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-loads purpose, then usage, then exclusions in three tight labeled blocks. Every sentence carries routing or behavioral instruction; nothing is redundant with the schema or annotations.

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 still tells the agent what the results mean and how to present them. All 8 parameters are documented in the schema and grouped in the description. Minor gap: it doesn't restate pagination/default-limit behavior, though the schema's cursor and limit descriptions cover that adequately.

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. The description adds real semantic value beyond the schema by grouping the eight parameters into lookup-by-identity (email/phone_number/external_id) versus filter-by-audience (list_id/tag_id), which tells the agent how to choose among them rather than just what each does.

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 contacts, or look one person up') and immediately distinguishes the two modes of operation. An agent can tell it apart from the singular get-contact sibling and from get-list/get-tag without opening any 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?

Explicit 'Use when' section maps real user phrasings ('is X a contact?', 'who has this tag?') to the correct parameter choice, and the 'Not for' section routes counting requests to get-list/get-tag by naming their contact_count output. Both when-to-use and when-not-to-use are covered with named alternatives.

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