set_api_credentials

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

With no annotations, the description carries the full burden and largely meets it: it discloses persistence ('Stored owner-only in <home>/.env') and the security semantics ('not secret in the way a login code is', 'identify the application, not the account'). It omits idempotency (overwrite behavior on repeat calls) and return/confirmation behavior.

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?

Front-loads the purpose in the first sentence, then separates rationale, source, storage, and an explicit Args list. Slightly verbose but every sentence adds usable context.

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?

Covers purpose, prerequisite, credential origin, storage, and both parameters. No output schema exists, so return values need not be described; only repeat-call behavior and failure modes are 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% (only bare titles), so the description must compensate and mostly does: api_id documented as 'numeric', api_hash as '32-character', both sourced from my.telegram.org. Minor tension: schema types both as string while the description calls api_id 'numeric', which could confuse the agent.

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+resource: 'Save the Telegram app credentials.' The phrase 'needed before any login' distinguishes it from the login_* siblings 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?

Establishes the prerequisite ordering ('before any login'), which tells the agent when this step belongs in the flow, and the source for obtaining values. It stops short of naming the specific alternative tools (login_request_code/login_submit_code) or stating when NOT to call it.

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