AWS Agent Toolkit IDE Errors? Clash Split Rules for IAM & Tool APIs (2026)

Why Agent Toolkit Is More Than “Another MCP Hop”

AWS positions the Agent Toolkit for AWS as the umbrella that bundles the AWS MCP Server, curated agent skills, IDE plugins, and rules files that steer AI coding agents toward documented procedures instead of hallucinated service picks. That layered story matters on the wire. A single user gesture might resolve plugin metadata from IDE toolkit endpoints, download hosted notification JSON, open an MCP session against a regional *.api.aws hostname, refresh credentials through STS, authorize actions via IAM, call a regional data-plane API, and still pull contextual snippets from language-server infrastructure if Amazon Q components sit beside the toolkit inside your editor.

This breadth is why the problem class differs from a narrowly scoped AWS MCP Server routing guide. That article remains essential for STS, IAM, and amazonaws.com hygiene—yet Agent Toolkit searches in 2026 frequently arrive with symptoms tied to bootstrap hosts that never appear in generic MCP write-ups. Likewise, the broader Model Context Protocol routing tutorial teaches patterns without naming the toolkit-specific allow lists AWS publishes for VS Code firewalls. Pair all three: conceptual MCP discipline, AWS-shaped credential routing, and the explicit toolkit domains below.

Throughout this piece, Clash refers to modern Mihomo-compatible cores consumed through Clash Verge-style clients unless noted otherwise. The engineering invariant remains unchanged: the first matching rule wins, DNS fake-ip only helps when every consumer actually asks Mihomo for answers, and domestic-direct expectations stay healthy only when your CN geo shortcuts sit below narrowly scoped overseas lanes rather than above them.

Symptoms That Masquerade as AWS Outages

Support threads cluster around partial failures. Agent skills enumerate correctly yet stall when execution reaches AWS APIs; the MCP channel connects intermittently while documentation search succeeds; device flows launch a browser tab that completes even though the IDE never observes token exchange; regional calls report timeout despite sts.amazonaws.com answering quickly; hosted notification downloads retry forever; language-server telemetry floods logs while interactive chat stays offline. Each variant hints at transport fragmentation rather than mysterious IAM bugs—especially when operators confirm that the same account works from a laptop tethered without split introspection.

Before rewriting IAM policies, reproduce once with Mihomo’s connection table sorted by hostname. Agent Toolkit almost always reveals the missing lane within the first handful of rows: perhaps idetoolkits.amazonwebservices.com fell through to GEOIP,CN,DIRECT, perhaps MCP traffic targeted *.api.aws while your profile only listed amazonaws.com, perhaps SSO redirected through oidc.region.amazonaws.com that never earned an explicit rule. The remainder of this guide turns those observations into durable YAML without encouraging blunt global proxy toggles that punish domestic teams.

Toolkit, MCP, IAM, and STS Surfaces You Actually Route

Treat the following list as a baseline allow-list skeleton sourced from AWS-maintained documentation for IDE tooling firewalls, then extend it with traces from your organization. Partitions, opt-in regions, private SaaS IdPs, and air-gapped mirrors all introduce suffixes no static article can freeze forever.

• Toolkit bootstrap and hosted files: AWS documents https://idetoolkits.amazonwebservices.com/endpoints.json plus notification JSON under idetoolkits-hostedfiles.amazonaws.com. Plugins typically reach wider prefixes on those hosts for configuration assets.
• MCP on api.aws: Managed MCP endpoints publish under regional *.api.aws hostnames (for example, patterns resembling aws-mcp.us-east-1.api.aws). If your rules only match amazonaws.com, MCP stays orphaned.
• STS and IAM: Global and regional STS hosts (sts.amazonaws.com, sts.us-east-1.amazonaws.com, peers in your working regions) partner with iam.amazonaws.com and partition-specific equivalents for control-plane calls Agent Toolkit issues once skills leave read-only documentation mode.
• Regional data planes: Prefixed service endpoints such as ec2.ap-northeast-1.amazonaws.com continue to dominate execution-heavy workflows even when MCP fronts the conversation.
• Console, sign-in, and SSO: Flows that bounce humans through signin.aws.amazon.com, IAM Identity Center portals, *.sso.region.amazonaws.com, *.sso-portal.region.amazonaws.com, and oidc.region.amazonaws.com remain relevant whenever toolkit plugins orchestrate browser-assisted authentication.
• Amazon Q adjacent endpoints: AWS groups language-server hosts such as aws-language-servers.us-east-1.amazonaws.com, telemetry sinks like client-telemetry.us-east-1.amazonaws.com, and conversational APIs including codewhisperer.us-east-1.amazonaws.com and q.us-east-1.amazonaws.com inside the same firewall annex. If your IDE installs both Agent Toolkit and Q-derived assistants, assume overlapping traffic even when you only “care” about MCP.
• Documentation and static assets: Skills that hydrate context may pull from docs.aws.amazon.com, aws.amazon.com, CloudFront fronts, or GitHub schema URLs referenced in the toolkit docs. Promote anything your trace proves necessary; avoid lazy MATCH,PROXY bludgeons when CN-direct defaults must remain intact.

The overlap with console browsing explains persistent confusion: the browser might honor OS proxy settings while the IDE extension host opens parallel sockets that ignore them until you introduce mixed-port variables or TUN capture. Aligning those stacks is half the battle; enumerating suffixes is the other.

Proxy-Groups, Rule Order, and an AWS_AGENTToolkit Lane

Create a dedicated outbound collection—call it AWS_AGENTToolkit—implemented as a conservative select or lightly tuned url-test. Hang toolkit, MCP, IAM, STS, regional API, and SSO host buckets on that lane using explicit DOMAIN-SUFFIX and DOMAIN rows before aggressive GEOIP,CN,DIRECT shortcuts. If community rule providers prepend noisy keyword matches, diff the merged artifact whenever subscriptions refresh; silent reordering is the leading regression vector for “it worked yesterday” MCP incidents.

Illustrative excerpt—rename proxies, prune redundancy, and extend suffixes only after your logs justify them:

proxy-groups:
  - name: AWS_AGENTToolkit
    type: select
    proxies:
      - NODE-TYO
      - NODE-PDX
      - DIRECT

rules:
  - DOMAIN,idetoolkits.amazonwebservices.com,AWS_AGENTToolkit
  - DOMAIN-SUFFIX,idetoolkits-hostedfiles.amazonaws.com,AWS_AGENTToolkit
  - DOMAIN-SUFFIX,api.aws,AWS_AGENTToolkit
  - DOMAIN-SUFFIX,amazonaws.com,AWS_AGENTToolkit
  - DOMAIN-SUFFIX,aws.amazon.com,AWS_AGENTToolkit
  - DOMAIN,signin.aws.amazon.com,AWS_AGENTToolkit
  - DOMAIN,console.aws.amazon.com,AWS_AGENTToolkit
  # SSO / Identity Center examples — confirm regions & IdP hosts from traces
  - DOMAIN-SUFFIX,sso.us-east-1.amazonaws.com,AWS_AGENTToolkit
  - DOMAIN-SUFFIX,oidc.us-east-1.amazonaws.com,AWS_AGENTToolkit
  # Optional Amazon Q / language-server lane if installed
  - DOMAIN-SUFFIX,aws-language-servers.us-east-1.amazonaws.com,AWS_AGENTToolkit
  - DOMAIN,q.us-east-1.amazonaws.com,AWS_AGENTToolkit
  - GEOIP,CN,DIRECT
  - MATCH,PROXY

Notice how DOMAIN-SUFFIX,api.aws sits beside amazonaws.com: omitting the newer suffix strands MCP while legacy SDK traffic appears healthy. When compliance mandates separating MCP from data-plane calls, clone the structure into two groups with divergent outbounds—but avoid doubling complexity until measurements prove it matters.

For readers still mastering matcher semantics, the friendly narrative lives in the split-traffic tutorial; return here afterward to specialize Agent Toolkit labels rather than relearning basics.

DNS Fake-IP, Resolver Bypass, and IDE Extension Hosts

DNS fake-ip accelerates domain-based policies only when every participant resolves through Mihomo. macOS Secure DNS profiles, browser-only DoH, or hard-coded upstreams inside helper binaries slice the chain: STS answers leave Mihomo, synthesized IPs never trigger your DOMAIN rows, and Agent Toolkit retries until users blame IAM. Enable hijack or TUN DNS capture once LAN printers and captive portals have documented exceptions, then re-run the failing skill while watching whether STS rows finally attach to AWS_AGENTToolkit.

Where TLS arrives IP-first, Sniffer-style SNI reconstruction can rescue classification, but treat it as instrumentation—not permission to skip logging. AWS endpoints generally expose useful SNI, yet enterprise builds occasionally ship exotic transports. Record proof before toggling advanced knobs.

Editor ergonomics vary: Electron shells may respect system proxy tables on Windows yet ignore them on certain Linux distributions unless environment variables wrap child processes. Cursor-specific pitfalls intersect the Cursor IDE routing guide; Agent Toolkit layers AWS-shaped endpoints on top of those behaviors rather than replacing them.

IAM and STS Reality Checks Inside Agent Toolkit

Agent Toolkit intentionally routes authenticated execution through your existing IAM principals and surfaces MCP-aware condition keys in CloudTrail. Routing fixes never substitute for least privilege: if policies deny ec2:RunInstances, Clash cannot help. Conversely, IAM alone cannot fix sockets that never reach Oregon because they were classified as domestic direct by an overeager geo rule.

When debugging, separate three planes: (1) credential acquisition via STS and SSO web flows, (2) discovery traffic for skills and documentation, (3) mutating API calls against regional endpoints. Map each plane to hostnames in your trace before merging diagnostics threads; mixing them produces contradictory advice in forums.

Organizations federating through IAM Identity Center should expect additional portal hosts and regional SSO endpoints beyond the snippet above. AWS publishes exhaustive SSO firewall guidance—mirror whatever regions your directory actually uses instead of cargo-culting us-east-1 literals.

Log-Backed Verification Steps

Use this repeatable checklist whenever Agent Toolkit misbehaves after subscription churn:

1. Reload Mihomo, open the connection inspector, and filter substrings such as idetoolkits, api.aws, amazonaws, sso, and your corporate IdP keyword.
2. Trigger the smallest failing operation—a metadata fetch, a read-only describe call, or MCP handshake—and freeze the table before entries scroll away.
3. Promote any unseen hostname ahead of GEOIP lines, redeploy, and confirm the matching rule column reads AWS_AGENTToolkit (or your chosen label).
4. From the shell that inherits IDE environment variables (or after exporting HTTPS_PROXY to the Mihomo mixed port), run curl -I https://sts.amazonaws.com, curl -I https://iam.amazonaws.com, and one logged MCP URL; latency matters less than consistent exit selection.
5. If browser involvement exists, complete the visible login once and immediately watch for fresh SSO or portal domains; insert them before retry loops amplify noise.
6. Archive the working triple—core version, DNS mode, snippet hash—in your internal runbook so the next upgrade compares facts rather than vibes.

Longitudinal stability favors conservative nodes that finish TLS over flashy relays that spike jitter mid-stream—especially when MCP multiplexes multiple AWS calls per assistant reply.

When TUN Helps—and When It Masks Bugs

Selective TUN capture rescues binaries that refuse proxy environment variables, yet global TUN routinely collateralizes domestic SaaS, LAN diagnostics, or banking apps that depended on split tunnels. Walk the ladder: explicit DOMAIN rows, mixed-port env injection for CLI helpers, targeted TUN with bypass lists, and only then broader capture. Deep dives on trade-offs live beside the Clash TUN mode guide; Agent Toolkit does not waive those cautions.

FAQ

Do I still need the AWS MCP split article if I followed this one?

Yes. MCP-centric guidance drills STS ordering edge cases and regional partitions with examples Agent Toolkit inherits wholesale. This article adds toolkit bootstrap hosts and api.aws naming that MCP-only searches overlook. Treat them as complementary bookmarks, not duplicates.

I only installed Agent Toolkit—why do Q endpoints appear?

IDE marketplaces frequently bundle Amazon Q language servers or telemetry alongside AWS-branded extensions. Even dormant components may phone home during startup. Either route those suffixes intentionally or uninstall unused packs; ignoring them risks false negatives when you grep logs for “amazonaws”.

Can I keep MCP on a separate outbound for auditing?

Absolutely—duplicate groups (AWS_MCP versus AWS_DATA) help when compliance mandates distinct egress IPs. Document the rationale inline so automatic rule merges do not flatten your separation silently.

Closing Thoughts

AWS Agent Toolkit succeeds when engineers respect its multi-plane architecture: curated skills, MCP transports, IAM-governed APIs, STS-backed credentials, and IDE-specific bootstrap infrastructure all move together. Clash split rules excel at expressing that complexity as ordered policy—provided DNS, capture depth, and subscription hygiene receive the same rigor as cloud IAM.

Many casual helper apps either force everything through a single tunnel—breaking domestic workflows that still need crisp latency—or ship frozen domain lists that fall behind the moment AWS adds another api.aws hostname or toolkit manifest path, which turns intermittent IDE timeouts into recurring fire drills. ClashSource stays oriented toward diff-friendly Mihomo policy, connection telemetry you can trust, and desktop clients in the Clash Verge lineage that make first-match behavior visible instead of mystical; if you want that operational posture without assembling binaries by hand, download ClashSource for free and drop the AWS_AGENTToolkit lane from this guide onto your existing profile.