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

Annotations already declare readOnly/idempotent/non-destructive, and the description still adds value beyond them: cost ("Free"), what is returned (public username plus https://t.me/username link, or an invite link for private channels), and a prompt-injection warning that channel-written text is data, not instructions. That last point is behaviorally important for an agent consuming untrusted text.

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, front-loaded with the read tag and the lookup key, then the downstream action. Every clause carries distinct information (source of id, return shape, next step, injection caveat) with no repetition of schema or annotations.

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?

With no output schema, the description compensates by describing exactly what comes back (username, public or invite link). For a single-parameter read tool with full annotation coverage, nothing needed 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 0% — `directory_id` has no description at all — so the description carries the burden, and it does explain the parameter's provenance (obtained from search_tg_channels). It does not state the type or what happens on an unknown id, keeping it below a 5.

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 ("One channel of the directory by its `directory_id`") and pins its position in the workflow by citing search_tg_channels as the id source. An agent can distinguish it from listing/searching siblings like search_tg_channels or list_tg_targets 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?

Gives concrete when-to-use context: the id must come from search_tg_channels, and the returned `link` is meant to be handed to join_tg_target. It stops short of explicit exclusions (e.g. when to prefer get_tg_campaign or list_tg_targets), but the positive routing is clear.

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