Agent Builder Toolkit

AI Agent Debugging & Integration Toolkit

Use AI to build. Use DDT to verify. Your AI coding tool can help build and debug the integration. DDT gives you an independent, deterministic view of the artifact it produced or consumed.

DDT's Agent Builder Toolkit checks tool calls, MCP and function-calling artifacts, JSON Schema, and OpenAPI without starting another AI task.

Analyze Locally
  • PrivateSensitive artifacts stay in this browser.
  • DeterministicReal validators, parsers and diff engines.
  • InstantPaste, inspect, result.

Inspect one artifact

Agent Tool Inspector

Paste a tool response, contract, auth header, OpenAPI change, or retrieved text. Get a concise local report, then open a finding in the relevant DDT tool when you need more detail.

Ctrl/⌘ + Enter

Runs in your browser. Your pasted payload is not sent to DDT servers. Analyzer code is loaded from DDT only when required; artifact content is not included in those requests.

Safe synthetic sample

Debug an agent response in 60 seconds

The response and expected contract differ by one field name. Copy both samples, format the response, then compare them in JSON Diff.

  1. Copy the actual response.
  2. Format and validate it.
  3. Copy the expected response and compare both payloads.
Actual agent response
{
  "tool": "get_order_status",
  "requestId": "req_demo_1042",
  "status": "completed",
  "result": {
    "orderId": "ORD-1042",
    "deliveryDate": "2026-09-08"
  }
}
Expected response
{
  "tool": "get_order_status",
  "requestId": "req_demo_1042",
  "status": "completed",
  "result": {
    "orderId": "ORD-1042",
    "estimatedDeliveryDate": "2026-09-08"
  }
}

Before it runs

Build the integration

Define the tools your agent can call, prove the API behind them returns what you promised, and catch a breaking change before it reaches production.

Tool definitions

Validate a tool definition schema

Check the JSON Schema an agent's tool or function definition declares, before a model ever sees it. Catch malformed types, missing required entries, and constraints that will not validate.

Validate a schema Inspect the schema's structure

Test data

Generate fixtures from that schema

Turn the schema you just validated into realistic, schema-valid sample payloads, so you can exercise an agent's handling of a tool result without calling the live API. Seeded output reruns identically.

Generate sample data

API contracts

Generate contract tests for an agent's API

Turn an OpenAPI spec into runnable contract tests, so the API behind a tool call keeps returning the shape your tool definition promised.

Generate contract tests

Spec drift

Catch a breaking API change before your agent does

Diff two versions of an OpenAPI spec and see which changes are breaking, risky or safe. A field an upstream team renamed is a tool call your agent silently starts getting wrong.

Compare two specs

Authentication

Set up the agent's authentication

Sign and verify JWTs (HS/RS/ES) and generate PKCE values while wiring an agent into an OAuth flow — the build-time counterpart to diagnosing a 401 later.

Use throwaway keys here. Signing with a production secret means pasting that secret into a page.

Sign a token or build PKCE

Before it acts

Screen what your agent reads

Anything an agent retrieves is untrusted input, and the text a model reads is not always the text you see.

Untrusted input

Inspect untrusted content before your agent acts on it

Zero-width characters, bidirectional overrides, and homoglyph substitutions can carry instructions that are invisible in rendered output but fully present in the text a model reads. Reveal them in retrieved pages, documents, and tool results.

Finding nothing hidden is not proof that content is safe. This inspects characters; it is not a prompt-injection filter, and manual review still applies.

Inspect untrusted content

After it ran

Debug what came back

Start with the symptom. DDT will take you to the most relevant tool or guided sequence.

Contract mismatch

Compare expected and actual payloads

Find missing fields, changed values, type differences, and unexpected structure.

Compare payloads

Authentication

Diagnose authentication failures

Inspect JWT claims, timestamps, headers, and token structure while keeping verification limitations clear.

Decoding a JWT does not verify its signature or trustworthiness.

Inspect a JWT

Safe sharing

Sanitize before giving debugging data to AI

Scan logs, headers, JSON and configuration for credentials or tokens before pasting them into Codex, Claude, ChatGPT, Copilot, a ticket, or a PR.

Pattern-based scanning can produce false positives and false negatives. Manual review is required.

Scan and redact secrets Sanitize a full HAR trace

Encoding

Decode encoded content

Decode Base64, Base64URL, and data URIs to read a payload that arrived encoded.

Decode encoded content

Reusable sequences

Repeatable debugging paths

Use a prebuilt workflow when one tool is not enough. Each step runs locally in your browser where the underlying tool supports it.

Canonical tools

Featured tools for agent builders

Secrets Scanner

Find and redact likely credentials before sharing agent debugging evidence. Manual review remains required.

JSON Diff

Compare two JSON payloads, ignoring key order.

JWT Decoder

Decode JWTs locally and verify HMAC signatures with a supplied secret.

HAR Sanitizer

Redact secrets with custom rules, and export Postman, cURL, or fetch packs.

Contextual utilities: JSON Formatter, cURL Converter, Base64, and Regex Tester. Regex is useful for testing custom detection patterns, but it is not a core agent-integration diagnostic.

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Companion, not competitor

AI can write the integration. DDT helps you verify what actually happened.

Use Codex, Claude Code, Cursor, GitHub Copilot, OpenAI agent tooling, LangChain, LangGraph, CrewAI, Google ADK, Semantic Kernel, MCP tooling, or your custom framework when it fits the job. Use DDT for a quick independent check of a specific payload, schema, token, trace, or API contract.

Privacy by architecture

Developer data should stay under your control

DDT tools process data in the browser. That is especially useful when debugging tokens, API payloads, logs, and traces that may contain sensitive information. Review each tool's guidance, avoid pasting production secrets unless necessary, and manually inspect anything before sharing it.

  • Tool data is processed in your browser.
  • No account is required for core usage.
  • No cookies or third-party analytics. Coarse allowlisted interaction categories may be counted at the CDN edge; raw tool input is never included.
  • Manual review remains necessary before sharing sensitive artifacts.

Read the technical privacy policy.

FAQ

Frequently asked questions

  • Are these tools specific to one agent framework?

    No. They address common integration problems involving JSON, HTTP, authentication, encoded data, traces, and contracts. They can support developers using different models and frameworks.

  • Does DDT upload my payloads or tokens?

    No. DDT tools process pasted data locally in your browser. The Toolkit sends only coarse allowlisted interaction categories to the same-origin CDN edge; it never sends tool input. There are no cookies or third-party analytics.

  • Can DDT verify that a JWT is valid?

    Decoding exposes the token structure and claims. It does not by itself verify the signature, issuer, audience, trust chain, or authorization decision. The JWT Decoder can separately verify supported HMAC signatures when you provide the secret.

  • Why not just use Codex or Claude Code?

    You should use them when they are the right tool. AI coding assistants are excellent for writing integrations, changing code, generating tests and reasoning across a repository. DDT serves a narrower purpose: quick, deterministic inspection of specific artifacts using browser-side validators, parsers, diff engines and security utilities.

  • Can I use the toolkit offline?

    Some tools are available after the site has been cached or installed, subject to current browser and PWA support.

  • Is this an official AgentsNexus resource?

    No. It is an independent Daily Developer Tools community resource and is not affiliated with or endorsed by AgentsNexus or its organizers.

Keep it close

Keep the toolkit ready for your next agent-building session

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