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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is covered. The description adds real behavior beyond that: the tool returns a link that should be included in the reply, and the input must be a photo-type message. It stops short of describing image format/size limits or failure modes, so it is not a full 5.

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?

Four short sentences, each with a distinct job: purpose, input precondition, sibling for the multi-photo case, and the required link-in-reply behavior. The main purpose is front-loaded and there is no filler.

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?

No output schema exists, yet the description still discloses the salient return value (a link to include in the reply) and the input precondition. For a two-parameter read tool with full annotation coverage, nothing an agent needs in order to call it correctly is missing.

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 two parameters are already documented and the baseline is 3. The description adds a genuine semantic constraint the schema lacks: the message_id must refer to a message whose message_type is 'photo', which is meaningful selection criteria.

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 ("Look at a Telegram photo") plus the concrete goals it enables (describe, OCR, answer questions). It also explicitly distinguishes itself from two siblings, telegram_get_photos and telegram_show_photo, so the agent can route without opening a 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?

Gives the exact selection condition (a message whose message_type is 'photo'), names the alternative for multiple photos (telegram_get_photos), and names the alternative for mere display (telegram_show_photo). When-to-use and when-not-to-use are both covered explicitly.

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