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nexus-browser

by pironjulien
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browser_wait_download

Read-onlyIdempotent

Waits for a tab-triggered download to finish and returns its file path, size, and MIME type, so agents can verify completed downloads.

Instructions

Waits for a download started in the tab (link click...) to finish and returns its path, size (bytes) and type (mime). Candidates: downloads started since the agent's last action on the tab (or since_ms, a timestamp in milliseconds), coming from the tab's origin. A file Chrome flags as dangerous is never accepted by the agent: explicit error. timeout_ms: at most 115000.

Input Schema

NameRequiredDescriptionDefault
tab_idYesYour tab's id (from browser_new_tab, or a tab adopted with browser_adopt_tab).
since_msNo
timeout_msNo

Output Schema

NameRequiredDescriptionDefault
dataYes
statusYes
warningNoEmergency stop hotkey not held, or similar notice
untrusted_noteNoPage text that looks like instructions aimed at an AI

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed10 schema fields changedv2.31.6
    • addedOutput schema / $defs
      Added value: +{
+  "FinishedDownload": {
+    "additionalProperties": true,
+    "properties": {
+      "bytes": {
+        "type": "number"
+      },
+      "bytesReceived": {
+        "type": "number"
+      },
+      "danger": {
+        "type": "string"
+      },
+      "dialog": {
+        "$ref": "#/$defs/PageDialog"
+      },
+      "dialogOpened": {
+        "type": "boolean"
+      },
+      "endTime": {
+        "anyOf": [
+          {
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "exists": {
+        "type": "boolean"
+      },
+      "id": {
+        "type": "integer"
+      },
+      "message": {
+        "type": "string"
+      },
+      "mime": {
+        "type": "string"
+      },
+      "path": {
+        "anyOf": [
+          {
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "pendingDialogs": {
+        "items": {
+          "$ref": "#/$defs/PageDialog"
+        },
+        "type": "array"
+      },
+      "referrer": {
+        "anyOf": [
+          {
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "startTime": {
+        "type": "string"
+      },
+      "state": {
+        "type": "string"
+      },
+      "success": {
+        "type": "boolean"
+      },
+      "url": {
+        "type": "string"
+      },
+      "waited_ms": {
+        "type": "number"
+      }
+    },
+    "title": "FinishedDownload",
+    "type": "object"
+  },
+  "PageDialog": {
+    "additionalProperties": true,
+    "description": "Dialog opened by the page (never accepted by the agent: browser_handle_dialog).",
+    "properties": {
+      "defaultPrompt": {
+        "type": "string"
+      },
+      "message": {
+        "type": "string"
+      },
+      "tabId": {
+        "type": "integer"
+      },
+      "type": {
+        "type": "string"
+      },
+      "url": {
+        "type": "string"
+      }
+    },
+    "title": "PageDialog",
+    "type": "object"
+  }
+}
    • addedOutput schema / additionalProperties
      Added value: +true
    • addedOutput schema / description
      Added value: +"The finished download."
    • addedOutput schema / properties / data
      Added value: +{
+  "$ref": "#/$defs/FinishedDownload"
+}
    • removedOutput schema / properties / result
      Removed value: -{
-  "title": "Result",
-  "type": "string"
-}
    • addedOutput schema / properties / status
      Added value: +{
+  "const": "success",
+  "type": "string"
+}
    • addedOutput schema / properties / untrusted_note
      Added value: +{
+  "description": "Page text that looks like instructions aimed at an AI",
+  "type": "string"
+}
    • addedOutput schema / properties / warning
      Added value: +{
+  "description": "Emergency stop hotkey not held, or similar notice",
+  "type": "string"
+}
    • changedOutput schema / required
      Previous value: -[
-  "result"
-]New value: +[
+  "status",
+  "data"
+]
    • changedOutput schema / title
      Previous value: -"browser_wait_downloadOutput"New value: +"WaitDownloadAnswer"
  2. First observedv0.1.0

TDQS

A4.2/5.0
Behavior5/5

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

Adds substantial behavior beyond the annotations: candidate selection window, the origin restriction, an explicit error for files Chrome flags as dangerous (a real failure mode the agent must handle), and a hard cap on timeout_ms (115000) that is absent from the schema. The annotations already cover the read-only/idempotent profile, so this is additive context rather than repetition.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the core action and return values, then the eligibility rules and the timeout cap. Dense and telegraphic ('link click...', 'type (mime)'), but every sentence carries information and nothing is redundant.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists, yet the description still summarizes the returned fields, and it covers the two gaps that matter for correct invocation: the timeout ceiling and the dangerous-file error path. Remaining gap is the relationship to browser_download_status, which an agent might need to disambiguate.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is only 33% — tab_id is documented but since_ms and timeout_ms are not — and the description compensates well: since_ms is defined as a millisecond timestamp with the default falling back to 'the agent's last action', and timeout_ms gets a maximum of 115000 that the schema does not declare. It loses a point only for the terse phrasing that leaves the precise semantics of 'last action' slightly implicit.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('waits for a download started in the tab... to finish') and even names the return payload (path, size in bytes, mime type). It is clearly distinct from a generic wait tool, though it never contrasts itself with the sibling browser_download_status, leaving the agent to infer the difference between waiting for a download and querying download state.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives a concrete usage context — a download triggered by a link click in the tab — and defines which downloads are eligible ('started since the agent's last action on the tab (or since_ms)') plus an origin constraint. It does not explicitly say when to prefer this over browser_download_status, so no explicit alternative routing.

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

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