list_contacts

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

With no annotations provided, the description carries the full burden. It discloses that the tool returns contacts from the local store (no network calls), includes names and phone numbers, and supports substring filtering. While it does not mention potential limits or error cases, for a simple read operation this is sufficiently transparent.

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 description is three concise sentences. The first explains the core action, the second describes the optional parameter, and the third points to a related sibling tool. Every sentence adds value, with no redundancy or fluff.

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 simple one-parameter tool with no output schema, the description is complete. It tells the agent what the tool returns (contacts with names and numbers), how to filter, and where to go for more detailed profile information. No gaps remain for effective use.

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?

The input schema already covers the search parameter with a case-insensitive substring match description. The description adds minimal extra meaning ('by name or number substring'), which is consistent but not significantly enhancing beyond the schema. Given 100% schema coverage, a baseline of 3 is appropriate.

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 clearly states the tool lists all Signal contacts known to the account, specifies what is included (names and phone numbers), and distinguishes it by mentioning the local store. It also contrasts with the sibling tool get_profile, providing clarity on its unique purpose.

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 explains when to use the optional search parameter (to filter by name or number substring) and directs users to get_profile for fetching Signal profiles. However, it does not explicitly differentiate from other listing tools like list_conversations or list_groups, though the context implies contact-specific usage.

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