## Summary
- Improve tool call error messages across 4 libraries (arcade-core,
arcade-tdk, arcade-mcp-server, arcade-serve) so agents can self-correct
and Datadog can facet on structured fields
- Guard empty error messages, enrich input validation errors with
field-level detail, fix `@tool` decorator fallback formatting, surface
`additional_prompt_content` in MCP responses, and add structured log
extras for Datadog
- Addresses the 3 worst error patterns: generic "Error in tool input
deserialization", bare `KeyError` values, and empty `FatalToolError`
messages
**Linear:** TOO-627
**Plan:** `docs/plans/2026-04-08-improve-error-messages-handoff.md`
## Tasks
- [ ] Task 1: Guard empty error messages (arcade-core)
- [ ] Task 2: Enrich input validation error messages (arcade-core)
- [ ] Task 3: Improve `@tool` decorator error fallback (arcade-tdk)
- [ ] Task 4: Fix MCP agent-facing error response (arcade-mcp-server)
- [ ] Task 5: Add structured log extras in BaseWorker (arcade-serve)
- [ ] Task 6: Add structured log extras in MCP server
(arcade-mcp-server)
## Test plan
- [ ] Each task has dedicated unit tests verifying the new behavior
- [ ] `make test` passes after all tasks
- [ ] `make check` (ruff + mypy) passes
- [ ] Verify the 3 worst error patterns now produce actionable messages
🤖 Generated with [Claude Code](https://claude.com/claude-code)
<!-- CURSOR_SUMMARY -->
---
> [!NOTE]
> **Medium Risk**
> Touches cross-library error formatting and logging behavior used in
production tool execution paths; while mostly additive/guardrails, it
changes agent-visible messages and Datadog log facets, which could
impact client expectations and alerting.
>
> **Overview**
> Improves tool-call error handling across core/runtime, MCP transport,
worker transport, and the TDK to make agent-visible failures more
actionable while *reducing sensitive-data leakage*.
>
> In `arcade-core`, empty error messages now get placeholders,
`ToolOutputFactory.fail*` defaults blank messages, and input validation
errors are rewritten as field-level summaries that intentionally omit
rejected values (avoiding Pydantic echo of secrets). The `@tool`
fallback in `arcade-tdk` no longer surfaces `str(exception)` to agents;
it returns exception *type-only* in `message` while preserving full
detail in `developer_message`.
>
> Adds a shared `build_tool_error_log_extra` helper and updates
`arcade-serve` + `arcade-mcp-server` to emit consistent structured
WARNING logs (`error_*`, `tool_name`, optional toolkit/version) for
Datadog, while MCP error responses now append
`additional_prompt_content` and force `structuredContent=None` on
failures per spec. Includes extensive new tests and bumps package
versions (`arcade-core` 4.6.2, `arcade-tdk` 3.6.1, `arcade-mcp-server`
1.19.3, `arcade-serve` 3.2.3).
>
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
e5c7ebcaf56176cfbd8e6d1f2b6295352abd0ec0. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->
---------
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
We recently added outputSchema support for our MCP tools (not yet for
worker routes yet). Today, we always return structuredContent. On tool
execution errors we return structuredContent: {"error": "..."} with
isError: True, even when that shape does not match the tool’s declared
outputSchema. Since the MCP spec says clients SHOULD validate
structuredContent against outputSchema, some clients reject these
responses.
Since structuredContent is optional, we’re going to omit it when
isError: true.
<!-- CURSOR_SUMMARY -->
---
> [!NOTE]
> **Medium Risk**
> Changes the shape of tool error responses across the MCP server, which
may break clients or tools that previously relied on
`structuredContent["error"]` for failures. Behavior is more
spec-compliant but touches core request/response paths and test
expectations.
>
> **Overview**
> Prevents MCP tool error responses from violating a tool’s declared
`outputSchema` by **always setting `structuredContent=None` when
`isError=True`** (server execution errors, unknown tools, middleware
exceptions, and `Context.tools.call_raw` JSON-RPC errors).
>
> Updates requirement-failure error formatting to put the human-friendly
message in `content[0]` and (when present) serialize extra
machine-readable fields (e.g. `authorization_url`, `llm_instructions`)
into an additional `content` item. Examples and integration/unit tests
are updated to read errors from `content[0].text`, and
`arcade-mcp-server` is bumped to `1.19.2`.
>
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
4213bdd4aa44362de85c30f5f31c576243c132d5. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->
Resolves
https://linear.app/arcadedev/issue/TOO-590/add-resources-support-to-server-framework
<!-- CURSOR_SUMMARY -->
---
> [!NOTE]
> **Medium Risk**
> Adds new resource registration/reading semantics (including URI
templates and duplicate/multiple-match policies) and changes JSON Schema
generation for tool I/O, which may affect MCP client compatibility and
runtime behavior across servers.
>
> **Overview**
> **Adds first-class MCP Resources support across `arcade-mcp-server`.**
`MCPApp` can now register resources at build time via
`add_resource`/`@resource` plus convenience `add_text_resource` and
`add_file_resource`, and passes these through to `MCPServer` for startup
loading (including `ResourceTemplate` URIs with `{param}` and `{param*}`
matching).
>
> **Extends `ResourceManager` behavior.** Resource reads now coerce
handler return types (including raw `bytes` to base64
`BlobResourceContents`), support template matching with
overlap/multiple-match detection, and introduce configurable duplicate
handling policies.
>
> **Improves tool schema + MCP Apps linking.** Tool input/output JSON
Schema generation is refactored to recursively expand nested `json`
schemas and ensure `outputSchema` is always an object (wrapping
non-object returns in a `result` property); `MCPApp` also supports
attaching arbitrary tool `_meta` extensions (e.g., `ui.resourceUri`)
applied at server start.
>
> Adds two new example servers (`resources`, `tools_with_output_schema`)
and broad test coverage for resource templates, static/file resources,
meta extensions, and schema wrapping/recursion.
>
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
e785bee79d74110727519b00b81dcad6e9b74212. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->
---------
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
# Valuable references for the reviewer:
- Docs PR: https://github.com/ArcadeAI/docs/pull/583
- Implements Phase 1 of the following planning doc:
https://linear.app/arcadedev/project/arcade-mcp-supports-mcp-auth-front-door-auth-7cbaa20cb054/overviewhttps://github.com/user-attachments/assets/79ad43fd-f5e8-4793-a1dd-18b35acefdc3
# PR Description
Adds OAuth 2.1 Resource Server authentication to arcade-mcp-server,
enabling HTTP MCP servers to validate Bearer tokens on every request.
This unlocks tool-level authorization and secrets support for HTTP
servers.
- Multiple authorization server support
- Granular token validation options (verify_exp, verify_iat, verify_iss)
- Environment variable configuration
- OAuth discovery metadata endpoint
(/.well-known/oauth-protected-resource)
- Extracts sub claim from token as context.user_id
- Lifts transport restrictions for tools requiring auth/secrets on HTTP
when protected
```python
from arcade_mcp_server import MCPApp
from arcade_mcp_server.resource_server import ResourceServerAuth, AuthorizationServerEntry
resource_server_auth = ResourceServerAuth(
canonical_url="http://127.0.0.1:8000/mcp",
authorization_servers=[
AuthorizationServerEntry(
authorization_server_url="https://auth.example.com",
issuer="https://auth.example.com",
jwks_uri="https://auth.example.com/jwks",
)
],
)
app = MCPApp(name="my_server", version="1.0.0", auth=resource_server_auth)
```
# Testing
Beyond the comprehensive unit tests, I also manually tested end-to-end
with WorkOS Authkit (DCR) and KeyCloak (non-DCR).
# Future Work
- CIMD support
- An `ArcadeResourceServer` to make adding front-door auth super easy
when using Arcade's Auth Server
<!-- CURSOR_SUMMARY -->
---
> [!NOTE]
> Adds OAuth 2.1 front-door auth (JWKS validation + OAuth discovery) and
propagates user identity to tools, enabling auth/secret-requiring tools
over HTTP.
>
> - **Authentication (Front-Door OAuth 2.1)**
> - New `resource_server` module with `ResourceServerAuth`
(multi-authorization-server, metadata) and `JWKSTokenValidator`
(JWKS-based JWT validation) plus granular validation options.
> - ASGI `ResourceServerMiddleware` validates Bearer tokens on every
HTTP request and injects `resource_owner`.
> - OAuth discovery endpoint via FastAPI router at
`/.well-known/oauth-protected-resource[/<path>]`.
> - **Integration**
> - `MCPApp`/`worker` accept `auth`/`resource_server_validator`, mount
middleware, expose discovery; logs accepted auth servers.
> - HTTP transport (`http_streamable`) carries `SessionMessage` with
`resource_owner` from request → session.
> - `Context`/`Session`/`Server` plumb `resource_owner`; `Server`
selects `user_id` preferring token `sub`.
> - **Behavior Changes**
> - HTTP transport restriction lifted for tools requiring
`authorization`/`secrets` when request is authenticated; otherwise
blocked with actionable error.
> - **Configuration**
> - Env-var based auth config via `MCP_RESOURCE_SERVER_*` in
`MCPSettings.ResourceServerSettings`; `.env` auto-load.
> - **Telemetry**
> - Usage tracking records `resource_server_type` on server start.
> - **Examples**
> - New `examples/mcp_servers/authorization` sample server (HTTP auth,
secrets, Reddit tool) with Docker setup.
> - **Tests**
> - Extensive unit tests for validators, middleware, env config,
multi-AS, transport rules, and app integration.
> - **Version**
> - Bump `arcade-mcp-server` to `1.12.0`; minor docstring tweak in
`__init__.py`.
>
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
d1116cdcafb0c7cb8f91e66682eb1fbae380da31. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->
Resolves TOO-152
# Release Candidate 2
## This PR:
- [x] No more confusing 307 redirect logs when using `/mcp` instead of
`/mcp/` (requested by @shubcodes)
- [x] Fix bug in `arcade configure` for Python < 3.12 (reported by
@evantahler
- [x] Fix bug where tools with unsatisfied secret requirements could
still be executed (reported by @evantahler, @shubcodes)
- [x] Auth providers can now be imported via `from
arcade_mcp_server.auth import Reddit` (requested by @shubcodes)
- [x] Add complete E2E oauth flow for tool calls with informational
errors about how to log into arcade and where to go to authorize
(requested by @evantahler, @shubcodes)
- [x] Add OAuth tool in `arcade new`'s generated server (requested by
@shubcodes)
- [x] Standardize on defaulting to running servers on port 8000
- [x] Improve credentials.yaml reading logic
- [x] CLI user friendliness (requested by @Spartee)
- [x] Remove `arcade serve` CLI command
- [x] Fix race condition in `arcade logout`
- [x] Update docs for desired developer onboarding flow
## Next PRs:
- Get `arcade deploy` working for MCP servers. (Command is hidden for
now)
- Rename all occurrences of `toolkit` to `server`/`tools` and rename all
occurrences of `worker` to `server`
Versions:
* arcade-mcp\==1.0.0rc1
* arcade-mcp-server\==1.0.0rc1
* arcade-core\==2.5.0rc1
* arcade-tdk\==2.6.0rc1
* arcade-serve\==2.2.0rc1
### Summary
Adds first-class MCP support across Arcade, introduces a new MCP server
and CLI, unifies the project under the arcade-mcp name, overhauls
templates/scaffolding, and improves developer tooling, secrets
management, and examples.
### Highlights
- **MCP Server & Core**
- New MCP server with stdio and HTTP/SSE transports, session management,
resumability, and lifecycle handling.
- FastAPI-like `MCPApp` for building servers with lazy init; integrated
worker+MCP HTTP app option.
- Middleware system (logging and error handling), robust exception
hierarchy, and Pydantic-based settings.
- Async-safe managers for tools, resources, and prompts backed by
registries and locks.
- Developer-facing, transport-agnostic runtime context interfaces (logs,
tools, prompts, resources, sampling, UI, notifications).
- Conversion from Arcade ToolDefinition to MCP tool schema; OpenAI JSON
tool schema converter.
- Parser supports `@app.tool`/`@app.tool(...)` decorators.
- **CLI**
- New `mcp` command to run MCP servers with stdio or HTTP/SSE.
- New `secret` command to set/list/unset tool secrets (supports .env
input, preserves original casing for lookups).
- `new` command refactored; option to create a full toolkit package with
scaffolding.
- `chat` command removed.
- `serve.py` imports updated to `arcade_serve.fastapi.telemetry`;
version retrieval now uses `arcade-mcp`.
- `show.py` refactor to use new local catalog utilities.
- `display_tool_details` improved: adds “Default” column and handles
nested properties.
- **Configuration & Discovery**
- New `configure.py` to set up Claude Desktop, Cursor, and VS Code to
connect to local or Arcade Cloud MCP servers.
- Discovery utilities to find/install toolkits, build `ToolCatalog`s,
analyze files for tools, load kits from directories (pyproject parsing),
and build minimal toolkits.
- Better handling of provider API key resolution and evaluation suite
loading.
- **Templates & Scaffolding**
- Reorganized template structure (minimal vs full); moved
`.pre-commit-config.yaml`, `.ruff.toml`, license, Makefile, README,
tests, and tools layout to correct paths.
- Minimal template adds `.env.example` for runtime secret injection.
- Template pyproject updated for MCP servers; includes sample server
with greeting and secret-reveal tools.
- Authorization flow in templates simplified.
- **Repo-wide Renaming & Examples**
- Migrates references from `arcade-ai` to `arcade-mcp` across READMEs,
scripts, and package metadata.
- Examples updated (LangChain/LangGraph/AI SDK/TypeScript) and package
name changed to `arcade-mcp-sdk`.
- **Evals & Core Utilities**
- Evals now use OpenAI tooling format (`OpenAIToolList`, `to_openai`);
`tool_eval` takes `provider_api_key`.
- Core utilities: fixed `does_function_return_value` by dedenting before
parse; version bump to `2.5.0rc1` and dependency cleanup.
- **Tooling & CI**
- `setup-uv-env` action splits toolkit vs contrib dependency
installation.
- Pre-commit: excludes `libs/arcade-mcp-server/mkdocs.yml` and
`libs/tests/` from YAML and Ruff hooks; Ruff per-file ignores (e.g.,
C901 in `libs/**/*.py`, TRY400 in server docs paths).
- Makefile updates for uv env setup, quality checks, tests, builds, and
new `shell` target.
- Added Makefile to MCP server library to streamline dev workflow.
- **Cleanup**
- Removed `claude.json` config.
- Simplified stdio entrypoint; removed unused imports (`arcade_gmail`,
`arcade_search`).
### Breaking Changes
- **CLI**: `chat` command removed; use `mcp`, `secret`, and updated
`new`.
- **Naming**: All users should update references from `arcade-ai` to
`arcade-mcp`.
- **Templates**: File paths moved; downstream scripts referencing old
template locations may need updates.
### Getting Started
- Run an MCP server:
- `arcade mcp --stdio --toolkits your_toolkit`
- `arcade mcp --http --toolkits your_toolkit`
- Manage secrets:
- `arcade secret set your_toolkit KEY=value`
- `arcade secret list your_toolkit`
- `arcade secret unset your_toolkit KEY`
- Configure clients:
- `arcade configure` to set up Claude Desktop, Cursor, and VS Code for
local/Arcade Cloud MCP.
---------
Co-authored-by: Sam Partee <sam@arcade-ai.com>
Co-authored-by: Shub <125150494+shubcodes@users.noreply.github.com>
Francisco Or Something
