Agent applications are increasingly adopted to automate workflows across diverse tasks. However, due to the heterogeneous domains they operate in, it is challenging to create a scalable evaluation framework. Prior works each employ their own methods to determine task success, such as database lookups, regex match, etc., adding complexity to the development of a unified agent evaluation approach. Moreover, they do not systematically account for the user's role nor expertise in the interaction, providing incomplete insights into the agent's performance. We argue that effective agent evaluation goes beyond correctness alone, incorporating conversation quality, efficiency and systematic diagnosis of agent errors. To address this, we introduce the TED framework (Talk, Evaluate, Diagnose). (1) Talk: We leverage reusable, generic expert and non-expert user persona templates for user-agent interaction. (2) Evaluate: We adapt existing datasets by representing subgoals-such as tool signatures, and responses-as natural language grading notes, evaluated automatically with LLM-as-a-judge. We propose new metrics that capture both turn efficiency and intermediate progress of the agent complementing the user-aware setup. (3) Diagnose: We introduce an automated error analysis tool that analyzes the inconsistencies of the judge and agents, uncovering common errors, and providing actionable feedback for agent improvement. We show that our TED framework reveals new insights regarding agent performance across models and user expertise levels. We also demonstrate potential gains in agent performance with peaks of 8-10% on our proposed metrics after incorporating the identified error remedies into the agent's design.
Figures & tables
Figure 1: Our proposed two-step automated error discovery approach that automatically identifies common errors of the agent based on judge and agent inconsistencies. Identical error colors indicate that similar low-level errors are clustered into the same high-level category.
Agent Model
MeanProg@k
MaxProg@k
MaxAUC@k
MaxPPT@k
pass@k
τ2 -bench Airline Domain (Easy)
gpt-4.1
0.95 | 0.82
1.00 | 1.00
0.99 | 0.81
0.80 | 0.50
1.00 | 1.00
gpt-4o
0.79 | 0.86
1.00 | 1.00
0.96 | 0.86
0.70 | 0.53
1.00 | 1.00
gpt-4o-mini
0.70 | 0.61
0.90 | 0.90
0.85 | 0.73
0.60 | 0.37
0.80 | 0.80
gpt-5
0.92 | 0.92
1.00 | 1.00
0.97 | 0.88
0.67 | 0.54
1.00 | 1.00
mistral-nemo
0.87 | 0.49
1.00 | 0.80
0.97 | 0.67
0.67 | 0.48
1.00 | 0.60
Table 1: Overall performance of different agent models on τ2 -bench airline and ToolSandbox, using gpt-4.1 as user proxy and LLM-as-a judge. Results are displayed with scores for Expert Persona | Non-expert Persona. For metrics with @k , the number of trials is n=k=20 for τ2 -bench and n=k=8 for ToolSandbox. MaxProgressRate@k is abbreviated as MaxProg@k .
Figure 3: E[progress(i,Gi,τil)] (dot) and Var[progress(i,Gi,τil)] (error bar) on τ2 -bench gpt-4o-mini agent using non-expert user proxy gpt-4.1. Each dot is an agent trajectory from a single trial and each task sample from the airline domain is evaluated using n=k=20 agent trials. We display only three example samples here. Sample 14 belongs to the hard split and others in the easy split.
Agent Model
τ2 -bench Airline Domain (Easy)
τ2 -bench Airline Domain (Easy + Hard)
pass@k
pass ^ 4
pass ^ k
pass@k
pass ^ 4
pass ^ k
gpt-4.1
1.00
0.60
0.20
0.76
0.29
0.10
gpt-4o
0.80
0.40
0.20
0.57
0.13
0.05
gpt-4o-mini
1.00
0.28
0.20
0.67
0.10
0.05
mistral-nemo
0.80
0.06
0.00
0.43
0.01
0.00
mistral-large
1.00
0.16
0.00
0.71
0.07
0.00
Table 2: Comparison of different agent models using the evaluation paradigm from the τ2 -bench ( Barres et al., 2025 ) original paper and their performances on the pass@k , pass ^ 4 , and pass ^ k metrics in the airline domain. The number of trials used is n=k=20 .
Agent Model
τ2 -bench Retail Domain
pass@k
pass ^ 4
pass ^ k
gpt-4.1
1.00
0.54
0.20
gpt-4o
1.00
0.43
0.04
gpt-4o-mini
0.92
0.23
0.04
mistral-nemo
0.76
0.08
0.00
mistral-large
0.96
0.33
0.08
Table 3: Comparison of different agent models using the evaluation paradigm from the τ2 -bench ( Barres et al., 2025 ) original paper and their performances on the pass@k , pass ^ 4 , and pass ^ k metrics in the retail domain. The number of trials used is n=k=20 .
Figure 4: (a) τ2 -bench airline sample_8 : mistral-nemo expert ( AUC =1.0, PPT =1.0) vs. gpt-4o-mini expert ( AUC =0.982, PPT =0.5) and mistral-nemo non-expert ( AUC =0.482, PPT =0.25) vs. gpt-4o-mini non-expert ( AUC =0.714, PPT =0.125) (b) τ2 -bench airline sample_8 : Barres et al. (2025) ’s original evaluation approach with n=k=20 trials.
Agent Model
ToolSandbox Dataset
(Base Scenarios)
(Base Scenarios + Variants)
MaxScoreM+@k
MaxScoreM+@k
gpt-4.1
0.92
0.90
gpt-4o
0.94
0.91
gpt-4o-mini
0.90
0.88
mistral-nemo
0.87
0.85
Table 4: Comparison of different agent models using the evaluation paradigm from the ToolSandbox ( Lu et al., 2024 ) original paper and their performances on the milestone similarity ScoreM+ metric. The number of trials used is n=k=8 .
Figure 5: τ2 -bench airline sample 14. The blue box shows a truncated task instruction i∈I for the non-expert user proxy gpt-4.1 model. The green boxes contain the truncated dialogue for trajectory 6 (left) and agent’s trajectory 18 (right). The agent model is gpt-4o-mini. The top-right box shows the errors identified. Zoom in for a larger view.
Table 5: Agent improvement results over the baseline agent for Expert Persona | Non-expert Persona, using gpt-4.1 as user proxy and LLM-as-a judge. Blue ↑ shows an improvement over the baseline agent, and red ↓ shows a decrease. We compare the gain in performance for several agent models using the Error Insertion (EI), Human Notes (HN), HiTEC-ICL (HTC) ( Cui et al., 2025 ) , and HTC † variant methods.
Appendix figures & tables25 assets
Supplementary material from the paper’s appendix.
Appendix
User Persona
Errors
Role confusion
Missing or violate instructions
Erroneous responses
Expert
0.0
0.06
0.0
Non-expert
0.0
0.125
0.0
Appendix
Table 6: Correctness of user proxy. Both agent and user proxy use gpt4.1 model.
Dataset
Cohen’s Kappa
τ2 -bench airline (42 subgoals from 10 samples)
0.84
ToolSandbox (31 subgoals from 10 samples)
0.92
Appendix
Table 7: Agreement between human and LLM-as-a-judge measured using Cohen’s Kappa. The agent uses gpt-5 model while the LLM-as-a-judge and the user proxy use gpt-4.1 model.
Dataset
Cohen’s Kappa
τ2 -bench airline (37 subgoals from 9 samples)
0.71
ToolSandbox (40 subgoals from 10 samples)
0.60
Appendix
Table 8: Agreement between human and LLM-as-a-judge measured using Cohen’s Kappa. The agent, LLM-as-judge, and user proxy use gpt-4.1 model.
Dataset
Cohen’s Kappa
τ2 -bench airline (27 subgoals from 10 samples)
0.90
ToolSandbox (32 subgoals from 10 samples)
0.80
Appendix
Table 9: Agreement between human and LLM-as-a-judge measured using Cohen’s Kappa. The agent uses gpt-4o model while the LLM-as-a-judge and the user proxy use gpt-4.1 model.
Dataset
Cohen’s Kappa
τ2 -bench airline (30 subgoals from 10 samples)
0.93
ToolSandbox (35 subgoals from 10 samples)
0.94
Appendix
Table 10: Agreement between human and LLM-as-a-judge measured using Cohen’s Kappa. The agent uses gpt-4o-mini model while the LLM-as-a-judge and the user proxy use gpt-4.1 model.
Dataset
Per-subgoal error
Disagreement with human
τ2 -bench airline (37 subgoals from 9 samples)
0.22
ToolSandbox (40 subgoals from 10 samples)
0.23
Appendix
Table 11: Correctness of the identified TED errors. The agent, LLM-as-a-judge, and user proxy use the gpt-4.1 model.
Dataset
Per-subgoal error
Disagreement with human
τ2 -bench airline (27 subgoals from 10 samples)
0.19
ToolSandbox (32 subgoals from 10 samples)
0.09
Appendix
Table 12: Correctness of the identified TED errors. The agent uses gpt-4o model while the LLM-as-a-judge and the user proxy use gpt-4.1 model.
Dataset
Per-subgoal error
Disagreement with human
τ2 -bench airline (30 subgoals from 10 samples)
0.23
ToolSandbox (35 subgoals from 10 samples)
0.06
Appendix
Table 13: Correctness of the identified TED errors. The agent uses gpt-4o-mini model while the LLM-as-a-judge and the user proxy use gpt-4.1 model.
Agent Model
MeanProg@k
MaxProg@k
MaxAUC@k
MaxPPT@k
Pass@k
τ2 -bench Airline Domain (Easy + Hard)
gpt-4.1
0.75 | 0.67
0.94 | 0.96
0.85 | 0.68
0.44 | 0.25
0.81 | 0.86
gpt-4o
0.63 | 0.55
0.91 | 0.88
0.84 | 0.65
0.44 | 0.23
0.81 | 0.71
gpt-4o-mini
0.53 | 0.53
0.86 | 0.88
0.79 | 0.66
0.43 | 0.26
0.62 | 0.76
gpt-5
0.80 | 0.77
0.96 | 0.97
0.89 | 0.77
0.47 | 0.30
0.91 | 0.91
mistral-nemo
0.67 | 0.36
0.96 | 0.71
0.87 | 0.56
0.44 | 0.25
0.86 | 0.38
Appendix
Table 14: Overall performance of different agent models on τ2 -bench airline domain, using gpt-4.1 as user proxy and LLM-as-a-judge. Dataset contains easy and hard samples. Results are displayed with scores for Expert Persona | Non-expert Persona. For metrics with @k , the number of trials is n=k=20 .
Agent Model
MeanProg@k
MaxProg@k
MaxAUC@k
MaxPPT@k
Pass@k
τ2 -bench Retail Domain
gpt-4.1
0.92 | 0.88
0.99 | 1.00
0.94 | 0.83
0.51 | 0.24
0.92 | 0.96
gpt-4o
0.87 | 0.75
1.00 | 0.99
0.95 | 0.83
0.54 | 0.25
1.00 | 0.96
gpt-4o-mini
0.81 | 0.76
1.00 | 0.98
0.95 | 0.82
0.54 | 0.25
1.00 | 0.88
mistral-nemo
0.57 | 0.58
0.99 | 0.97
0.86 | 0.79
0.29 | 0.23
0.88 | 0.84
mistral-large
0.80 | 0.81
1.00 | 1.00
0.94 | 0.83
0.49 | 0.23
0.96 | 1.00
Appendix
Table 15: Overall performance of different agent models on τ2 -bench retail domain, using gpt-4.1 as user proxy and LLM-as-a-judge. Results are displayed with scores for Expert Persona | Non-expert Persona. For metrics with @k , the number of trials is n=k=20 .
Figure 6: Scatter plot results on the τ2 -bench airline domain (easy + hard) illustrating the relationship between MaxAUC@k and MaxProgressRate@k (left subplot), and between MaxPPT@k and MaxProgressRate@k (right subplot) using the setting n=k=20 trials.
Figure 7: Dataset level performance of different agent models on the τ2 -bench airline domain (easy), with error bars representing 95% confidence intervals. The top graph shows the MaxProgressRate@k , middle graph shows MaxAUC@k , bottom graph shows MaxPPT@k .
Figure 8: Dataset level performance of different agent models on the ToolSandbox dataset, with error bars representing 95% confidence intervals. The top graph shows the MaxProgressRate@k , middle graph shows MaxAUC@k , bottom graph shows MaxPPT@k .
Figure 9: Dataset level performance of different agent models on the τ2 -bench airline domain (easy+hard), with error bars representing 95% confidence intervals. The top graph shows the MaxProgressRate@k , middle graph shows MaxAUC@k , bottom graph shows MaxPPT@k .
Figure 10: Dataset level performance of different agent models on the τ2 -bench retail domain, with error bars representing 95% confidence intervals. The top graph shows the MaxProgressRate@k , middle graph shows MaxAUC@k , bottom graph shows MaxPPT@k .
User Model
MeanProg@k
MaxProg@k
MaxAUC@k
MaxPPT@k
pass@k
τ2 -bench Airline Domain (Easy + Hard)
gpt-4.1
0.75 | 0.67
0.94 | 0.96
0.85 | 0.68
0.44 | 0.25
0.81 | 0.86
gpt-4o
0.72 | 0.61
0.95 | 0.95
0.82 | 0.66
0.36 | 0.22
0.81 | 0.81
gpt-4o-mini
0.73 | 0.64
0.95 | 0.95
0.80 | 0.65
0.35 | 0.22
0.86 | 0.86
gpt-5
0.71 | 0.73
0.92 | 0.95
0.85 | 0.83
0.46 | 0.37
0.76 | 0.86
Appendix
Table 16: Overall performance of a gpt-4.1 agent with different user proxy models on the τ2 -bench airline domain, using gpt-4.1 model as LLM-as-a-judge. Dataset contains easy and hard samples. Results are displayed with scores for Expert Persona | Non-expert Persona. For metrics with @k , the number of trials is n=k=20 .
Figure 11: Example of generated grading notes for the ToolSandbox sample modify_contact_with_message_recency .
Figure 12: Example of generated grading notes for the ToolSandbox sample update_contact_relationship_with_relationship_twice_multiple_user_turn .
Figure 13: Example of generated grading notes for the ToolSandbox sample find_current_city_low_battery_mode .
Figure 14: Example of generated grading notes for the ToolSandbox sample convert_currency .
Figure 15: Example of generated grading notes for the ToolSandbox sample search_message_with_recency_oldest .
Figure 16: Example of generated grading notes for the ToolSandbox sample search_reminder_with_recency_yesterday .
Figure 17: Example of user task instructions for the ToolSandbox samples
Figure 18: Example of user task instructions for the τ2 -bench airline samples
Figure 19: Agent dialogue excerpt for gpt-5 and Mistral-Nemo, illustrating how Mistral-Nemo makes tool calls early and quickly satisfies the grading notes, while gpt-5 asks clarifying questions and progresses more gradually. Despite these differing strategies, both agents complete the task in the same number of turns.