core/tools: show images instead of describing them

New `view_image` reads a local picture (JPEG, PNG, GIF, WebP, sniffed from its
bytes) and hands it to the model as an image part, with an optional `detail`
level — `low` measured 3.4x cheaper on a 1200x900 picture. `read_file` now
points at it instead of returning decode noise.

`fetch_local` returns an image response as the picture itself, and MCP image
content blocks become image parts instead of `[image: ...]` placeholders, so a
screenshot server finally reaches the model.

src/plyngent/cli/display.py

@@ -206,6 +206,19 @@ def _read_file_prefix(args_json: str) -> str:
     return _pretty_prefix(f"* Read '{path}' ")
 
 
+def _view_image_prefix(args_json: str) -> str:
+    """``* View image 'path' ``: the picture is already on its way to the model."""
+    path = _json_str_arg(args_json, "path") or "?"
+    return _pretty_prefix(f"* View image '{path}' ")
+
+
+def _view_image_detail(_args_json: str, result: str) -> str:
+    """``view_image`` outcome: the picture was attached, or why it was not."""
+    if result.startswith("error:"):
+        return _pretty_segments((f"({result.partition('error: ')[2]})", "red"))
+    return _pretty_segments(("(attached)", "green"))
+
+
 def _range_detail(result: str) -> str | None:
     """``L{begin}-{end} (done)`` detail of a ranged result, when it carries one."""
     first = result.splitlines()[0] if result else ""
@@ -896,6 +909,7 @@ def _skill_edit_detail(_args_json: str, result: str) -> str:
 # Pretty tools: ``prefix`` prints as the call starts, ``detail`` when it lands.
 _PRETTY_LINES: dict[str, PrettyLine] = {
     "read_file": PrettyLine(prefix=_read_file_prefix, detail=_read_file_detail),
+    "view_image": PrettyLine(prefix=_view_image_prefix, detail=_view_image_detail),
     "tree": PrettyLine(prefix=_tree_prefix, detail=_tree_detail),
     "todo_list": _todo_line("todo_list"),
     "todo_push": _todo_line("todo_push"),

src/plyngent/runtime/mcp_client.py

@@ -8,6 +8,7 @@ the process: start, tool listing, tool calls, reconnect, shutdown.
 from __future__ import annotations
 
 import asyncio
+import base64
 import importlib.metadata
 import json
 import os
@@ -17,6 +18,10 @@ from collections import deque
 from dataclasses import dataclass
 from typing import TYPE_CHECKING, cast
 
+from plyngent.agent.images import image_part_from_bytes
+from plyngent.agent.tools import ToolOutput
+from plyngent.lmproto.openai_compatible.model import ChatImagePart
+
 if TYPE_CHECKING:
     from typing import Any
 
@@ -84,9 +89,10 @@ class McpTool:
         )
 
 
-def _format_content(result: Json) -> str:
+def _format_content(result: Json) -> ToolOutput:
-    """Flatten a ``tools/call`` result payload into model-facing text."""
+    """Flatten a ``tools/call`` result payload into text plus any images."""
     parts: list[str] = []
+    images: list[ChatImagePart] = []
     for item in _json_list(result.get("content")):
         entry = _json_dict(item)
         kind = str(entry.get("type", ""))
@@ -94,12 +100,24 @@ def _format_content(result: Json) -> str:
             text = entry.get("text")
             if isinstance(text, str):
                 parts.append(text)
+        elif kind == "image":
+            # MCP carries an image as base64 + mimeType; the model wants the
+            # picture itself, not a ``[image: image/png]`` placeholder.
+            data = entry.get("data")
+            mime = entry.get("mimeType", "?")
+            part = image_part_from_bytes(base64.b64decode(data)) if isinstance(data, str) and data else None
+            if isinstance(part, ChatImagePart):
+                images.append(part)
+            elif isinstance(part, str):
+                parts.append(f"[image: {mime}] {part.removeprefix('error: ')}")
+            else:
+                parts.append(f"[image: {mime}]")
         elif kind == "resource":
             parts.append(f"[resource] {json.dumps(entry, ensure_ascii=False)}")
         else:
             mime = entry.get("mimeType", "?")
             parts.append(f"[{kind or 'unknown'}: {mime}]")
-    return "\n".join(parts)
+    return ToolOutput(text="\n".join(parts), images=images)
 
 
 class McpServerConnection:
@@ -307,17 +325,17 @@ class McpServerConnection:
             cursor = next_cursor
         return tools
 
-    async def call_tool(self, name: str, arguments: Json) -> str:
+    async def call_tool(self, name: str, arguments: Json) -> ToolOutput:
-        """Run ``tools/call`` and return the flattened text result.
+        """Run ``tools/call`` and return its text plus any images it produced.
 
         Tool-level failures (``isError``) come back as ``error: …`` text, not
         exceptions: the protocol round-trip itself succeeded.
         """
         result = await self._request("tools/call", {"name": name, "arguments": arguments})
-        text = _format_content(result)
+        output = _format_content(result)
         if result.get("isError") is True:
-            return f"error: {text or 'tool reported failure without content'}"
+            return ToolOutput(text=f"error: {output.text or 'tool reported failure without content'}")
-        return text
+        return output
 
 
 class McpManager:
@@ -393,7 +411,7 @@ class McpManager:
                 connection.tools = await connection.list_tools()
                 connection.tools_stale = False
 
-    async def call(self, server: str, tool: str, arguments: Json) -> str:
+    async def call(self, server: str, tool: str, arguments: Json) -> ToolOutput:
         connection = self._connections.get(server)
         if connection is None or not connection.connected:
             msg = f"server {server!r} is not connected"

src/plyngent/tools/file/__init__.py

@@ -11,10 +11,12 @@ from .listdir import listdir as listdir
 from .read import read_file as read_file
 from .regex_files import regex_files as regex_files
 from .tree import tree as tree
+from .view_image import view_image as view_image
 from .write import write_file as write_file
 
 FILE_TOOLS = [
     read_file,
+    view_image,
     write_file,
     listdir,
     tree,

src/plyngent/tools/file/read.py

@@ -4,6 +4,7 @@ from typing import cast
 
 from plyngent.agent import ToolTag, mark_lineno_read, tool
 from plyngent.agent.budget import DEFAULT_TOOL_RESULT_MAX_CHARS
+from plyngent.agent.images import sniff_image_media_type
 from plyngent.tools.truncate_token import TruncateToken, truncate_with_token, truncation_marker
 from plyngent.tools.workspace import AccessMode, resolve_path
 
@@ -39,9 +40,15 @@ def read_raw_text(path: str) -> tuple[str | None, str]:
 
     Shared by ``read_file`` and ``get_truncated`` so truncate-token char offsets
     always refer to the raw file text (never the ``L{begin}-{end}`` header).
-    Missing paths and directories are distinguished for the caller.
+    Missing paths and directories are distinguished for the caller, and a picture
+    is answered with the tool that shows it instead of decode noise.
     """
     target = resolve_path(path, required=AccessMode.READ)
+    if target.is_file():
+        with target.open("rb") as handle:
+            media_type = sniff_image_media_type(handle.read(16))
+        if media_type is not None:
+            return None, f"error: {path} is an image ({media_type}); use view_image to look at it"
     if not target.exists():
         return None, f"error: file not found: {path}"
     if not target.is_file():
@@ -71,6 +78,8 @@ async def read_file(
     ``DEFAULT_TOOL_RESULT_MAX_CHARS``); a ``truncate_token`` is appended when cut
     so ``get_truncated`` can continue reading the rest without a new request.
     Pass ``max_chars < 1`` to read unbounded.
+
+    An image file is refused with a pointer to ``view_image``, which shows it.
     """
     target = resolve_path(path, required=AccessMode.READ)
     text, err = read_raw_text(path)

src/plyngent/tools/file/view_image.py

@@ -0,0 +1,42 @@
+"""Model-facing ``view_image``: hand a local picture to the model as a picture."""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, cast
+
+from plyngent.agent import ToolOutput, ToolTag, tool
+from plyngent.agent.images import image_part_from_bytes
+from plyngent.tools.workspace import AccessMode, resolve_path
+
+if TYPE_CHECKING:
+    from plyngent.lmproto.openai_compatible.model import ImageDetail
+
+_DETAILS: frozenset[str] = frozenset({"low", "high", "original", "auto"})
+
+
+@tool(tags=ToolTag.LOCAL | ToolTag.INSTANCE_STATE | ToolTag.READ_ONLY)
+async def view_image(path: str, detail: str = "auto") -> str | ToolOutput:
+    """Look at an image file (JPEG, PNG, GIF, or WebP) under the workspace.
+
+    Use it for a screenshot, a chart, a diagram, or any other picture, instead
+    of ``read_file`` (which would return mojibake for those bytes).
+
+    ``detail`` trades tokens for fine visual detail: ``low`` downscales to
+    512x512 before inference — fast and cheap when only the layout matters, but
+    small text stops being readable — while ``high``/``original`` keep the
+    picture as it is, and ``auto`` (the default) lets the provider decide.
+
+    The format is read from the file's own bytes, so a misnamed file still
+    works; anything else comes back as an error.
+    """
+    if detail not in _DETAILS:
+        return f"error: detail must be one of {', '.join(sorted(_DETAILS))}"
+    target = resolve_path(path, required=AccessMode.READ)
+    if not target.exists():
+        return f"error: file not found: {path}"
+    if not target.is_file():
+        return f"error: not a file: {path}"
+    part = image_part_from_bytes(target.read_bytes(), detail=cast("ImageDetail", detail))
+    if isinstance(part, str):
+        return f"error: {path}: {part.removeprefix('error: ')}"
+    return ToolOutput(text=f"image: {path} (attached below)", images=[part])

src/plyngent/tools/mcp.py

@@ -15,7 +15,7 @@ from __future__ import annotations
 import re
 from typing import TYPE_CHECKING
 
-from plyngent.agent.tools import ToolDefinition, ToolTag
+from plyngent.agent.tools import ToolDefinition, ToolOutput, ToolTag
 from plyngent.tools.catalog import ToolSource, get_catalog
 
 if TYPE_CHECKING:
@@ -43,8 +43,8 @@ def _make_handler(
     manager: McpManager,
     server: str,
     tool: str,
-) -> Callable[..., Awaitable[str]]:
+) -> Callable[..., Awaitable[ToolOutput]]:
-    async def handler(**arguments: object) -> str:
+    async def handler(**arguments: object) -> ToolOutput:
         return await manager.call(server, tool, dict(arguments))
 
     return handler

src/plyngent/tools/net/client.py

@@ -7,6 +7,7 @@ from typing import TYPE_CHECKING, Any
 
 import niquests
 
+from plyngent.agent.images import sniff_image_media_type
 from plyngent.tools.net.grants import ensure_host_allowed
 from plyngent.tools.net.policy import (
     DEFAULT_MAX_BYTES,
@@ -50,7 +51,10 @@ class FetchResult:
     method: str
     security: str
     warnings: list[str] = field(default_factory=list)
-    body_kind: str = "text"  # text | binary | empty
+    body_kind: str = "text"  # text | binary | image | empty
+    # Raw bytes, kept only for an image body so the caller can hand the picture
+    # to the model instead of a hex preview.
+    body_image: bytes = b""
 
 
 def _content_type(headers: Mapping[str, str] | object | None) -> str:
@@ -132,6 +136,10 @@ def _body_payload(data: bytes, content_type: str) -> tuple[str, str]:
         return "empty", ""
     if _looks_text(content_type, data):
         return "text", _decode_body(data, content_type)
+    if sniff_image_media_type(data) is not None:
+        # An image is handed to the model as a picture, so the preview line only
+        # carries what the part cannot say itself.
+        return "image", f"(image body; content_type={content_type!r}; bytes={len(data)})"
     preview = data[:64].hex()
     return (
         "binary",
@@ -279,6 +287,7 @@ async def http_fetch(
                 ),
                 warnings=list(dict.fromkeys(warnings)),
                 body_kind=body_kind,
+                body_image=data if body_kind == "image" else b"",
             )
 
 

src/plyngent/tools/net/fetch_local.py

@@ -2,9 +2,10 @@
 
 from __future__ import annotations
 
-from plyngent.agent import ToolTag, tool
+from plyngent.agent import ToolOutput, ToolTag, tool
+from plyngent.agent.images import image_part_from_bytes
 from plyngent.tools.context import is_read_only_context
-from plyngent.tools.net.client import http_fetch
+from plyngent.tools.net.client import FetchResult, http_fetch
 from plyngent.tools.net.policy import (
     DEFAULT_MAX_BODY_CHARS_IN,
     DEFAULT_MAX_BYTES,
@@ -76,7 +77,7 @@ async def fetch_local(
     follow_redirects: bool = True,
     allow_http_downgrade: bool = False,
     offset: int = 0,
-) -> str:
+) -> str | ToolOutput:
     """HTTP request (GET/POST/PUT/DELETE); return status, metadata, and truncated body.
 
     Use for public docs/APIs or (after human policy allow) local/LAN servers.
@@ -88,6 +89,9 @@ async def fetch_local(
     User-Agent entry in ``headers``. A headers-only User-Agent is kept as-is.
     When both omit UA, a small default is used.
 
+    An image response (JPEG, PNG, GIF, WebP) comes back as the picture itself
+    beside that metadata, so you can look at it instead of reading a hex preview.
+
     Private/loopback/link-local hosts require an explicit human policy grant
     (not skipped by YOLO). HTTPS→HTTP redirects are blocked unless
     ``allow_http_downgrade`` is true.
@@ -121,7 +125,7 @@ async def fetch_local(
     except Exception as exc:  # noqa: BLE001 — tool surface returns error text
         return f"error: fetch_local failed: {exc}"
 
-    return format_fetch_result(
+    text = format_fetch_result(
         status=result.status,
         final_url=result.final_url,
         content_type=result.content_type,
@@ -136,6 +140,21 @@ async def fetch_local(
         max_chars=max_chars,
         offset=offset,
     )
+    return _attach_image(text, result)
+
+
+def _attach_image(text: str, result: FetchResult) -> str | ToolOutput:
+    """An image response is handed over as a picture, beside the usual metadata.
+
+    The preview line stays in the text so ``body_kind=image`` and the byte count
+    are still visible to the model.
+    """
+    if result.body_kind != "image" or not result.body_image:
+        return text
+    part = image_part_from_bytes(result.body_image)
+    if isinstance(part, str):
+        return f"{text}\n{part}"
+    return ToolOutput(text=text, images=[part])
 
 
 # Re-export for danger classifier without importing client.

tests/test_cli/test_mcp_cmd.py

@@ -68,7 +68,7 @@ async def test_slash_mcp_list_statuses(state: ReplState, capsys: pytest.CaptureF
         out = capsys.readouterr().out
         assert "fake" in out
         assert "connected" in out
-        assert "tools=3" in out
+        assert "tools=4" in out
     finally:
         await manager.aclose()
 
@@ -92,7 +92,7 @@ async def test_slash_mcp_reconnect_connects_new_config(
         statuses = state.mcp_manager.statuses()
         assert [name for name, _, _ in statuses] == ["fake"]
         assert statuses[0][1] == "connected"
-        assert statuses[0][2] == 3
+        assert statuses[0][2] == 4
         out = capsys.readouterr().out
         assert "tools=off" in out
         assert "fake" in out

tests/test_runtime/mcp_fake_server.py

@@ -11,6 +11,8 @@ import os
 import sys
 
 _FAKE_INSTRUCTIONS = os.environ.get("PLYNGENT_MCP_FAKE_INSTRUCTIONS", "")
+# A real 1x1 PNG (base64), what an image-carrying tool result looks like.
+_PNG_BASE64 = "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z8BQDwAEhQGAhKmMIQAAAABJRU5ErkJggg=="
 
 
 def respond(request_id: int, result: object) -> None:
@@ -61,6 +63,11 @@ def main() -> None:
                             "description": "Sleeps past any client timeout.",
                             "inputSchema": {"type": "object", "properties": {}},
                         },
+                        {
+                            "name": "shot",
+                            "description": "Returns a picture beside its text.",
+                            "inputSchema": {"type": "object", "properties": {}},
+                        },
                     ]
                 },
             )
@@ -75,6 +82,17 @@ def main() -> None:
                         "isError": False,
                     },
                 )
+            elif name == "shot":
+                respond(
+                    int(request_id),
+                    {
+                        "content": [
+                            {"type": "text", "text": "shot.png"},
+                            {"type": "image", "data": _PNG_BASE64, "mimeType": "image/png"},
+                        ],
+                        "isError": False,
+                    },
+                )
             elif name == "fail":
                 respond(
                     int(request_id),

tests/test_runtime/test_mcp_client.py

@@ -34,13 +34,28 @@ async def test_connection_handshake_lists_and_calls_tools() -> None:
         assert connection.connected
         assert connection.error is None
         assert connection.instructions is None
-        assert [tool.name for tool in connection.tools] == ["echo", "fail", "slow"]
+        assert [tool.name for tool in connection.tools] == ["echo", "fail", "slow", "shot"]
         echo = connection.tools[0]
         assert echo.description == "Echo the given text back."
         assert echo.input_schema["type"] == "object"
 
         result = await connection.call_tool("echo", {"text": "hello"})
-        assert result == "echo: hello"
+        assert result.text == "echo: hello"
+        assert result.images == []
+    finally:
+        await connection.aclose()
+
+
+async def test_an_image_content_block_becomes_an_image_part() -> None:
+    """A server that returns pixels gets them to the model, not a placeholder."""
+    connection = McpServerConnection("fake", _server_config())
+    await connection.start()
+    try:
+        output = await connection.call_tool("shot", {})
+
+        assert output.text == "shot.png"
+        assert len(output.images) == 1
+        assert output.images[0].image_url.url.startswith("data:image/png;base64,")
     finally:
         await connection.aclose()
 
@@ -64,7 +79,7 @@ async def test_tool_error_returns_error_text() -> None:
     await connection.start()
     try:
         result = await connection.call_tool("fail", {})
-        assert result == "error: boom"
+        assert result.text == "error: boom"
     finally:
         await connection.aclose()
 
@@ -122,9 +137,9 @@ async def test_manager_start_status_and_call() -> None:
     manager = McpManager(McpConfig(servers={"fake": _server_config()}, disable=[]))
     await manager.ensure_started()
     try:
-        assert [(name, status, count) for name, status, count in manager.statuses()] == [("fake", "connected", 3)]
+        assert [(name, status, count) for name, status, count in manager.statuses()] == [("fake", "connected", 4)]
         assert manager.instructions() == []
-        assert await manager.call("fake", "echo", {"text": "hi"}) == "echo: hi"
+        assert (await manager.call("fake", "echo", {"text": "hi"})).text == "echo: hi"
     finally:
         await manager.aclose()
     assert manager.statuses() == [("fake", "not started", 0)]
@@ -157,5 +172,5 @@ async def test_manager_disable_and_restart() -> None:
 
     await manager.restart(McpConfig(servers={"fake": _server_config()}, disable=[]))
     await manager.ensure_started()
-    assert manager.statuses() == [("fake", "connected", 3)]
+    assert manager.statuses() == [("fake", "connected", 4)]
     await manager.aclose()

tests/test_tools/test_catalog.py

@@ -59,6 +59,7 @@ def test_read_only_classification() -> None:
     read_only = {t.name for t in default_tool_definitions(surface="local") if t.tags & ToolTag.READ_ONLY}
     assert read_only == {
         "read_file",
+        "view_image",
         "get_truncated",
         "glob_paths",
         "regex_files",

tests/test_tools/test_fetch_local.py

@@ -2,12 +2,14 @@
 
 from __future__ import annotations
 
+import base64
 import threading
 from http.server import BaseHTTPRequestHandler, HTTPServer
 from typing import TYPE_CHECKING, override
 
 import pytest
 
+from plyngent.agent import ToolOutput
 from plyngent.tools.context import read_only_context
 from plyngent.tools.danger import classify_danger
 from plyngent.tools.net import fetch_local, grant_private_host
@@ -29,6 +31,12 @@ if TYPE_CHECKING:
     from pathlib import Path
 
 
+# A real 1x1 PNG: the body must be sniffed by its bytes, not by the header.
+_PNG_BYTES = base64.b64decode(
+    "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z8BQDwAEhQGAhKmMIQAAAABJRU5ErkJggg=="
+)
+
+
 class _Handler(BaseHTTPRequestHandler):
     """Minimal echo server for fetch_local tests."""
 
@@ -66,6 +74,9 @@ class _Handler(BaseHTTPRequestHandler):
         if self.path.startswith("/bin"):
             self._send(200, b"\x00\x01\x02\xffbinary", content_type="application/octet-stream")
             return
+        if self.path.startswith("/png"):
+            self._send(200, _PNG_BYTES, content_type="image/png")
+            return
         if self.path.startswith("/ua"):
             ua = (self.headers.get("User-Agent") or "").encode()
             self._send(200, ua)
@@ -200,6 +211,20 @@ async def test_fetch_get_post_put_delete(workspace: Path, http_server: str) -> N
     assert "status=204" in out_del
 
 
+async def test_an_image_response_comes_back_as_the_picture(workspace: Path, http_server: str) -> None:
+    """A PNG body is handed to the model as an image part, not a hex preview."""
+    del workspace
+    grant_private_host("127.0.0.1", int(http_server.rsplit(":", 1)[1]))
+
+    output: object = await fetch_local.handler(f"{http_server}/png")
+
+    assert isinstance(output, ToolOutput)
+    assert "body_kind=image" in output.text
+    assert "status=200" in output.text
+    part = output.images[0]
+    assert part.image_url.url.startswith("data:image/png;base64,")
+
+
 async def test_fetch_read_only_context_blocks_non_get(workspace: Path, http_server: str) -> None:
     """In a read-only context fetch_local only allows GET; outside it POST works."""
     del workspace

tests/test_tools/test_view_image.py

@@ -0,0 +1,68 @@
+"""``view_image``: a local picture reaches the model as a picture."""
+
+from __future__ import annotations
+
+import base64
+from typing import TYPE_CHECKING
+
+from plyngent.agent import ToolOutput
+from plyngent.tools.file.read import read_file
+from plyngent.tools.file.view_image import view_image
+
+if TYPE_CHECKING:
+    from pathlib import Path
+
+# A real 1x1 PNG: the format is sniffed from these bytes.
+PNG = base64.b64decode(
+    "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z8BQDwAEhQGAhKmMIQAAAABJRU5ErkJggg=="
+)
+
+
+async def test_view_image_attaches_the_picture(workspace: Path) -> None:
+    (workspace / "shot.png").write_bytes(PNG)
+
+    output = await view_image.handler("shot.png")
+
+    assert isinstance(output, ToolOutput)
+    assert output.text == "image: shot.png (attached below)"
+    url = output.images[0].image_url.url
+    assert url.startswith("data:image/png;base64,")
+    assert base64.b64decode(url.partition(",")[2]) == PNG
+
+
+async def test_the_detail_level_reaches_the_part(workspace: Path) -> None:
+    (workspace / "shot.png").write_bytes(PNG)
+
+    output = await view_image.handler("shot.png", detail="low")
+
+    assert isinstance(output, ToolOutput)
+    assert output.images[0].image_url.detail == "low"
+
+
+async def test_an_unknown_detail_level_is_an_error(workspace: Path) -> None:
+    (workspace / "shot.png").write_bytes(PNG)
+
+    assert "detail must be one of" in await view_image.handler("shot.png", detail="huge")
+
+
+async def test_a_non_image_file_is_an_error(workspace: Path) -> None:
+    (workspace / "notes.txt").write_text("hello")
+
+    result = await view_image.handler("notes.txt")
+
+    assert isinstance(result, str)
+    assert "not a JPEG, PNG, GIF, or WebP image" in result
+
+
+async def test_a_missing_file_is_an_error(workspace: Path) -> None:
+    del workspace
+
+    assert await view_image.handler("nope.png") == "error: file not found: nope.png"
+
+
+async def test_read_file_points_at_view_image_for_a_picture(workspace: Path) -> None:
+    (workspace / "shot.png").write_bytes(PNG)
+
+    result = await read_file.handler("shot.png")
+
+    assert result == "error: shot.png is an image (image/png); use view_image to look at it"