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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds that the search happens on a live channel and is a lookup that precedes an add, but says nothing about rate limits, behavior on no match, or result shape.

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?

The core instruction is front-loaded well, but the parenthetical instructs the same thing twice ('before calling contacts.sync' and 'use contacts.sync afterwards to actually add them') and repeats the 'before adding' idea, wasting the middle of the description.

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 live-channel search with no output schema, the description should signal what a successful lookup yields or what happens when nothing is found; neither is covered. Annotations plus the sync follow-up make it usable, but an agent cannot predict the response.

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 schema already documents query, channel and in_workspace; baseline is 3. The description adds only that query is a username or phone number (schema also allows a name), which is marginal value over the schema.

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?

State a specific verb (search/look up) plus resource (a person on a live channel by username or phone) and explicitly routes away from group discovery. However it never distinguishes itself from the near-identical sibling contacts_find, which an agent could easily confuse with this lookup.

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?

Gives clear when-to-use ('before calling contacts.sync', 'when asked to add or find a specific person by @username or phone') and names contacts.sync as the follow-up action plus an exclusion against group discovery. The absence of any guidance versus contacts_find is the one meaningful gap.

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