get_avatar

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

Beyond the readOnly/idempotent annotations, it discloses the source (copy signal-cli has stored), the return shape (identifier, base64, has_avatar), decode format, and the exact failure case 'Could not find avatar'. This is rich context that annotations alone would not provide.

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 front-loaded with the core action and avoids filler. It is a dense single paragraph, but every sentence contributes useful information; minor structural improvement could make the return and failure details easier to scan.

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?

There is no output schema, so the description carries the burden of explaining return values, and it does so thoroughly with identifier, base64, and has_avatar. It also covers the failure case, identifier types, and related update tools, making it complete for this one-parameter read 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 coverage is 100%, so the baseline is 3, but the description adds useful meaning: identifier is required, E.164 for contacts, group id from list_groups for groups, and anything not full E.164 is treated as a group id. That heuristic parsing rule goes beyond the schema description.

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 states a specific verb and resource: return a contact's or group's avatar image as base64. It distinguishes the contact vs. group identifier rules and names related setters (update_profile, update_group), so an agent can identify the tool 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?

It gives concrete identifier conditions and points to update_profile/update_group for setting avatars, which helps route the agent. It does not explicitly state when not to use this tool or name a retrieval alternative, so it has clear context but lacks full exclusion guidance.

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