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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), so the bar is lower. The description adds real value beyond that: it discloses the key capability limit (the model cannot see the image itself) and the rendering caveat that not every client draws the picture, so the returned link must be surfaced as clickable.

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?

Three tight sentences, zero filler, and the primary purpose plus the critical sibling distinction are front-loaded before the operational detail.

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?

Output schema exists, so return values need no explanation; the description still flags the returned link's use. Purpose, alternative routing, precondition, and rendering caveat together cover everything needed to invoke this correctly.

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. The description goes beyond the schema by constraining which message is valid — the chat_id/message_id must reference a message whose message_type is 'photo' — which the schema does not state.

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 ('Display a Telegram photo to the user as a picture in the conversation') and immediately distinguishes itself from the look-alike sibling telegram_get_photo. An agent can pick this over telegram_get_photo without opening either 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?

Explicitly names the alternative and the condition that selects it: 'This does not let you see the image — to describe it or read anything in it, use telegram_get_photo.' It also states the precondition that the target message must have message_type 'photo'.

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