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

With no annotations, the description carries the full behavioral burden. It does add one genuinely useful trait — 'Returns actual image' signals the payload is image data rather than a URL — but says nothing about authentication, private-account behavior, rate limits, or the case where neither identifier is supplied.

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 short sentences, zero filler, with the core action front-loaded and the trigger phrases and return note following. Every clause earns its place by aiding routing or invocation.

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 read tool with two optional identifiers and no output schema, the description adequately covers what it does and what it returns. The one gap is that no parameter is required, yet the description never explains how the target user is resolved when both are omitted.

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 both parameters are fully documented in the schema. The description adds no format, precedence, or fallback detail beyond what the schema already states ('Use either username or user_id'), so the baseline 3 applies.

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: 'Get and display user's profile photo.' No sibling tool in the list retrieves profile images, so the resource alone distinguishes it from get_user_by_id, get_user_by_username, and get_user_medias 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?

It gives explicit trigger phrases ('show photo', 'show picture', 'show avatar', 'покажи фото'), which is strong when-to-use guidance including a non-English invocation. It stops short of naming an alternative tool or stating when not to use it, so it is clear context without exclusions.

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