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

With only readOnlyHint=false available, the description carries the burden well: it discloses merge-not-replace semantics, deployment timing (next deploy, not restart), and that DATABASE_URL/MYSQL_* are protected — set_env rejects overrides and never drops them. These are non-obvious behaviors an agent could not infer from structured fields.

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, front-loaded with the core action, followed by timing and protection constraints. No filler and every sentence adds distinct information.

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 the mutation's risk profile, timing, and protected keys for a tool with no output schema. Minor gaps remain: no mention of the response/error shape on rejected overrides, and no statement of why both parameters are optional despite operating on a specific project.

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% and the nested env object has no property descriptions, so the description must compensate. 'Merge environment variables... existing keys are kept' conveys that env is a key/value map applied additively, but the 'project' parameter (name vs. id, and whether it is required given 0 required params) is never clarified.

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 ('Merge environment variables into a project') plus the key semantic detail that existing keys are kept. This clearly separates it from list_env (read) and deploy_project (apply), which the description also names.

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?

Explains the usage context precisely: changes only take effect on the next deploy_project, and a restart does NOT re-apply env. That is a real routing rule against restart_project. It stops short of naming read/alternative tools such as list_env, so it is clear context without explicit exclusions everywhere.

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